Design, Construction & Analysis of a Pulsejet Engine

1

University of Limerick

Design, Construction & Analysis of a Pulsejet

Engine

Prepared by: Thomas Naughton 0542717

Under the Supervision of: Dr. Patrick Frawley

Final Year Report Submitted to the University of Limerick, March, 2010

Aeronautical Engineering

I declare that this is my own work and that all contributions from other persons have

been appropriately identified and acknowledged

i

Abstract

This engineering reports the design construction and analysis of a pulsejet engine to

achieve static thrust. An engine was designed using available theory. Following a delay

due to ignition system problems, the completed engine was tested extensively in an

attempt to achieve static thrust. A detailed analysis of petal valve vibration was carried

out while attempting to get the engine to resonate. This included the experimental

verification of a mathematical model. Several tests were carried out using different petal

valve natural frequencies. The tests resulted in the engine being capable of achieving

sustained resonance without the external supply of air for up to two minutes. Petal valve

failure was determined to be the cause of the short running times. The operation of the

engine was analysed using available thermodynamic models but these models were

determined to be inaccurate for pulsejet cycle prediction. The pressure cycles within the

pulsejet engine were obtained experimentally using a high-temperature pressure

transducer. The resulting pressure/time plots were compared to other plots which were

obtained from published literature. The plots were found to correlate well together with

peak pressures measured in three very different sized engines being within 0.07 Bar of

each other.

ii

Acknowledgements

I would like to thank my supervisor, Dr. Patrick Frawley, for his support and guidance

throughout the project. Without his support this project would not exist.

I would like to thank the technical staff of the M&AE Department workshop for their

help with building the project. Especially Mr. Patrick O’Donnell, Mr. Ken Harris and

Mr. Jim Caulfield.

I would also like to thank the technicians of the Aeronautical Laboratory, Mr. Jim Ryan,

Mr. John Cunningham and Mr. Adrian McEvoy for their help throughout testing.

I would also like to thank the technical staff of the Electronic Engineering Department,

Mr. John Bird and Mr. John Clifford for their help with ignition system.

Finally, I would like to thank my family for their valuable support throughout the year.

iii

Table Of Contents

1. Introduction 1

1.1. Brief History 1

1.2. Operation 3

2. Objectives 5

3. Literature Review 6

3.1. Jet Design 7

3.2. Reed Valve Design 7

3.3. Thermodynamics 10

4. Conceptual Design 11

4.1. Valve System 12

4.2. Choice of Fuel 13

4.3. Fuel Delivery 14

4.4. Ignition System 16

4.5. Test Stand 17

5. Theory & Design 18

5.1. Jet Design 18

5.2. Petal Valve Vibration Frequency 23

5.3. Thermodynamic Analysis 28

5.4. Material Selection 30

6. Construction 36

6.1. Jet Body 36

6.2. Intake Diffuser 37

6.3. Valve Plates 38

6.4. Valve Retainer Plates 39

6.5. Petal Valve 40

6.6. Fuel Injection Nozzles 41

6.7. Test Stand 43

7. Testing & Troubleshooting 45

7.1. Ignition System Problems 45

7.2. Fuel Mixing 48

7.3. Valve Frequency Ratio Tuning 49

7.4. Valve Frequency High-Speed Camera Test 54

iv

7.5. Data Collection 55

8. Results 57

9. Discussion 59

9.1. Jet design 59

9.2. Petal Valve Vibration Theory 59

9.3. Valve Life 59

9.4. Valve Response to Engine Forcing Frequency 60

9.5. Ignition System 61

9.6. Thermodynamic Analysis 61

9.7. Pressure Cycle Visualisation 61

9.8. Exhaust Velocity Determination 62

10. Conclusion 63

References 64

Appendices

Appendix A – Engineering Drawings

Appendix B – Ignition Circuit Diagram

Appendix C – Electro-chemical Etching Process

Appendix D – Turn-it-in Originality Report Summary

Appendix E – Kistler Pressure Tranducer Data Sheets (CD)

Appendix F – Excel Spreadsheets (CD)

v

List of Figures

Figure 1.1 Marconnet pulsating combustor [Reynst, 1961] .............................................. 1

Figure 1.2 V-1 flying bomb with Argus AS-014 pulsejet engine [museumofflight.org,

2010] ................................................................................................................................. 2

Figure 1.3 Ignition Stage ................................................................................................... 3

Figure 1.4 Combustion/Power Stage ................................................................................ 3

Figure 1.5 Intake Stage ..................................................................................................... 4

Figure 1.6 Compression/Re-ignition Stage ....................................................................... 4

Figure 3.1 Pressure-Time plot example for 50cm valved pulsejet engine [Ordon, 2006] 6

Figure 3.2 Tharratt's mechanical valve which was claimed to withstand 25 hrs operation at full thrust [Tharratt, 1965] ……………………………….………………………….. 8

Figure 3.3 Cross-section of Standard Valve (left) and Low-loss Modified Valve (right) [Bressman, 1946] ………………………………………………………………………. 9

Figure 4.1 Argus AS-014 Grid Valve Layout [FZG-76 Geräte-Handbuch, 1944] …... 11

Figure 4.2 Aprilia RS125 Reed Valve Assembly ……………………………………. 12

Figure 4.3 Petal Valve ………………………………………………………………... 12

Figure 4.4 Normally Aspirated (left) and Injected (right) Fuel Delivery [aardvark.co.nz, 2009] ………………………………………………………………………………….. 14

Figure 4.5 Sketch of Valve Head Design ……………………………………………. 16

Figure 4.6 Piezoelectric Oven Igniter ………………………………………………… 17

Figure 4.7 CAD Model of Test Stand Used With Previous Project ………………….. 17

Figure 5.1 Intake Orifice Design ……………………………………………………... 22

Figure 5.2 Final Jet Body Dimensions ……………………………………………….. 23

Figure 5.3 Petal Valve Geometry …………………………………………………….. 24

Figure 5.4 Simplified Petal Valve Model …………………………………………….. 25

Figure 5.5 Petal Valve Geometry Split for Centroid Determination …………………. 26

Figure 5.6 Points of Interest Within the Pulsejet Engine …………………………….. 28

Figure 5.7 Ideal pulsejet cycle [El-Sayed, 2008] …………………………………….. 28

Figure 5.8 Pressure Cycle plot in AS-014 pulsejet engine [Bressman, 1946] ………... 31

Figure 5.9 Mechanical Properties of Grade 43A Steel at Elevated Temperatures [Bailey, 2009] ………………………………………………………………………………….. 33

vi

Figure 6.1 Combustion Chamber and Flange ………………………………………… 37

Figure 6.2 Intake Diffuser ……………………………………………………………. 38

Figure 6.3 Anodised Valve Plates; Original (left) & Modified (right) ……………….. 39

Figure 6.4 Valve Retainer Plate ………………………………………………………. 40

Figure 6.5 Electro-chemical Etching Apparatus ……………………………………… 41

Figure 6.6 Fuel Injection Nozzles; Internal (top) & External (bottom) ………………. 43

Figure 6.7 Engine Mounted on Test Stand …………………………………………… 44

Figure 7.1 Final Ignition Circuit ……………………………………………………… 47

Figure 7.2 Uneven Burning in the Combustion Chamber (left) & Burning With New Nozzle Fitted (right) ………………………………………………………………….. 48

Figure 7.3 Valve Motion Sign Convention (left) & Simplified Valve Motion Plot (right) ………………………………………………………………………………………….51

Figure 7.4 0.010" Deformed Shim Steel Valve Following Engine Run ……………….52

Figure 7.5 Impact and Fatigue Damage on a 0.006" Spring Steel Petal Valve ………. 53

Figure 7.6 High-Speed Camera Experiment Setup …………………………………... 55

Figure 7.7 Equipment Set Up For Pressure Data Collection …………………………. 56

Figure 8.1 55mm Position Pressure/Time Plot ……………………………………….. 57

Figure 8.2 1075mm Position Pressure/Time Plot …………………………………….. 58

vii

Nomenclature

Symbol Description Units

Area m2 Mean Cross Sectional Area m2

Exhaust Area m2

Valve Area m2

CNC Computer Numerically Controlled -

Specific Heat Capacity at Constant Pressure (cold) J/kg/K

Specific Heat Capacity at Constant Pressure (hot) J/kg/K

Specific Heat Capacity at Constant Volume (hot) J/kg/K

Diameter m

Combustion Chamber Diameter m

Exhaust Diameter m

Young’s Modulus of Elasticity GPa

Thrust N

FEM Finite Element Method -

Second Moment of Area m4

ID Internal Diameter m

Length m

Combustion Chamber Length m

Engine Length m

Mach Number -

NACA National Advisory Committee for Aeronautics -

OD Outside Diameter m

Static Pressure Pa

Stagnation Pressure Pa

Energy Density of Fuel J/kg

Universal Gas Constant J/kg/K

Static Temperature K

Stagnation Temperature K

Strain Energy J

Exhaust Velocity m/s

viii

Inlet Velocity m/s

Jet Velocity m/s

Volume m3

Engine Volume m3

Breadth of Beam m

Local Speed of Sound in Air m/s

Frequency Hz ℎ Heat Added Per Unit Mass J/kg

Spring Stiffness N/m

Mass of Lumped Mass kg

Mass of Beam kg

Mass Air Flow kg/s

Mass Fuel Flow kg/s

Radius m

Internal Radius m

External Radius m

Thickness m

Vertical Distance to Centroid m

Specific Heat Ratio (cold) -

Specific Heat Ratio (hot) -

Burner Efficiency -

Diffuser Efficiency -

Density kg/m3

Normal Stress Pa

Hoop Stress Pa

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2

through the inlet. At the same time the Argus engine company were developing

valveless pulsejet engines. Schmidt joined the Argus company and, in 1939, together

they successfully developed a valved pulsejet design which was later used to power the

unmanned V-1 flying bomb, (figure 1.2).

Figure 1.2 V-1 flying bomb with Argus AS-014 pulsejet engine [museumofflight.org, 2010]

Following the end of World War II, many of the Argus engines were captured by the

US and Russia. The captured engines were reverse engineered and analysed extensively

in an attempt to create a viable propulsive device for use on aircraft. The majority of

this testing has been documented and published by NACA. The main concern regarding

the pulsejet was the operating life of the reed valves in the front of the engine. Efforts

were made to increase the operating life but these were quickly overtaken by the

development of the turbojet engine. The turbo-jet engine offered increased reliability

and fuel efficiency and the pulsejet was largely forgotten as a source of aircraft

propulsion.

Today, small pulsejet engines still find use as radio control model powerplants. This is

mainly due to their simplicity and low cost when compared to a model turbojet of the

same size. Pulsejets have also paved the way for Pulse Detonation Engine (PDE)

technology which is a major research interest among aircraft manufacturers as a high-

tech, fuel efficient form of propulsion.

3

1.2. Operation

The operation of a pulsejet engine is similar to that of a modern reciprocating engine. It

operates in defined cycles which draw in air/fuel mixture, compress it, ignite it and

exhaust it in stages before the cycle repeats itself. The following figures 1.3 – 1.6 are

used to explain the cycles more clearly.

The first stage begins with the ignition of a fuel/air charge, figure 1.3. Ignition is

provided by a spark plug during start-up and by residual combustion during normal

operation.

Figure 1.3 Ignition Stage

The ignited fuel/air mix expands rapidly, increasing the pressure within the engine to

greater than atmospheric pressure. This forces the spring valves shut which then forces

the expanding gases to exit rapidly through the tailpipe producing thrust, (figure 1.4).

Figure 1.4 Combustion/Power Stage

Due to the Kadenacy effect, a partial vacuum is formed behind the rapidly escaping

exhaust gases. The pressure at the front of the engine is now lower than atmospheric

pressure. The pressure differential across the reed valves causes them to open and draws

fresh fuel/air mixture into the engine, (figure 1.5). At the same time, the pressure

difference within the engine slows down the momentum of the small proportion of

exhaust gases which have not yet exited the tailpipe and draws them back up towards

the front of the engine.

4

Figure 1.5 Intake Stage

The momentum of the small “piston” of burning exhaust gases which has been sucked

back into the engine helps to compress the fresh fuel/air charge and ignite it (figure 1.6)

and the cycle repeats itself. The cycle repeats itself 40-250 times per second depending

on the size and length of the engine.

Figure 1.6 Compression/Re-ignition Stage

The reed valves are the only moving part of the engine. The operating life of these

valves can vary from 1-2 minutes up to several hours depending on factors such as

valve material, valve construction and valve natural frequency. These factors are

discussed in more detail in section 3.2.

Partial Vacuum

5

2. Objectives

The main aims of the project were as follows:

To design and build a working pulsejet engine to provide static thrust

To analyse the operation of the engine both theoretically and experimentally so

as to gain a better understanding of the principles behind the operation of these

engines.

To investigate the pressure cycles within the engine during operation.

3. Liter

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In recent

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6

conducted

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7

An additional source of information for the project was a final year report submitted to

the University of Limerick by David Curran in 2004. This report details the construction

and testing of a valved pulsejet of similar design to the engine constructed during the

course of this project. Although the engine which was constructed in 2004 was not able

to self sustain without an external source of air, the recommendations for future work

given in the report were considered and referred to during the course of the design work.

3.1. Jet design

The most comprehensive paper found on pulsejet design was C.E. Tharratt’s “The

Propulsive Duct”. These were published as a series of articles in a journal entitled

“Aircraft Engineering and Aerospace Technology” between 1965 and 1966 while the

author was involved in research for the Chrysler Space Division, New Orleans. In these

articles, Tharratt attempted to produce a comprehensible theoretical approach to pulsejet

design and thermodynamic analysis. The first article proposed three basic equations

which one could use to successfully determine the basic dimensions of a pulsejet tube as

well as a theoretical analysis of the pulsejet thermodynamic cycle.

Several reports were published by Cornell Aeronautical Laboratory in the late 1940s as

part of the “Project Squid” experiment carried out for the United States Navy. These

reports were studied but much of their content was decided to be unnecessarily detailed

or irrelevant for the purposes of this project. Some content regarding reed valve design

was used and is detailed in section 3.2.

3.2. Reed Valve Design

Tharratt’s second article in “The Propulsive Duct” provides a brief overview of valve

design. Mechanical spring valves such as those used in the Argus engine and

aerodynamic valves used in all valveless designs are discussed in detail. Tharratt has

claimed that he developed a mechanical spring valve to “withstand 25hr. at full thrust”,

including “several continuous runs of 7hr. duration”. (Figure 3.2) This operating life is

much higher than those experienced by NACA during their tests on captured Argus

8

engines. Tharratt provides an image of this valve in the article but does not include

further details regarding its design or operating characteristics.

Figure 3.2 Tharratt's mechanical valve which was claimed to

withstand 25 hrs operation at full thrust [Tharratt, 1965]

A report published by Cornell Aeronautical Laboratory in 1947 entitled “4’x6” Pulsejet

Engine Project” contains a section in which reed valve material is discussed. The report

tested the performance of a pulsejet engine using reed valves of varying thickness and

materials and discussed the results briefly. According to this report, “annealed spring

steel or soft steel reeds are superior to tempered and polished spring steel reeds for

longevity”.

The tests also showed that “heavier reeds, in general, showed a longer life than thinner

reeds although operation of the jet was more difficult to start and resonance of the jet

was more easily upset when using heavy reeds than with the lighter reeds”.

These observations were taken into account when choosing the appropriate valve

material for the jet.

Two wartime reports published by NACA bear particular relevance to reed valve

design.

The first of these reports, written by Manganiello, Valerino & Breisch and published in

1945, attempts to solve the issue of poor reed valve operating life which had been

observed during earlier sea-level performance tests of a 22-inch pulsejet. The average

valve life was reported to be 30 minutes before the valve tips were damaged by the

repeated impact with the valve grid and a severe loss of thrust was observed as a result.

The authors attempted to extend the life of the valves on the same engine by coating the

valve grid with a thin layer of neoprene. The reasoning behind the neoprene coating was

to cushion

on the val

significant

valves wa

broken of

valves we

grid show

grid. The

due to the

The secon

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Figure

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as visible” a

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wed a signifi

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and “after

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9

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10

3.3. Thermodynamics

The pulsating nature of combustion in a pulsejet engine makes it very complicated to

analyse as the processes are time dependant. Due to the lack of interest in pulsejet

engines as source of aircraft propulsion, not much research has been done to accurately

predict the processes within them. Therefore, very little thermodynamic analysis of a

pulsejet engine can be found in modern literature.

The most modern analysis which was found was published as a small section in Ahmed

F. El-Sayed’s “Aircraft Propulsion and Gas Turbine Engines”. The analysis assumes

that combustion takes place at a constant volume process and that the exhaust gases

expand isentropically in the tailpipe. In reality, combustion in a pulsejet engine is

neither a constant-volume nor a constant-pressure process and, since most pulsejets

glow red-hot during operation, the expansion of exhaust gases cannot be accurately

modelled as isentropic. However, the analysis could provide an estimate of the pressure

and temperature conditions within the engine early on in the design process.

Another source of theoretical analysis was found in “Jet Propulsion”, a reference text

prepared by the Guggenheim Aeronautical Laboratory for the Air Technical Service

Command and published in 1946. This text also makes similar assumptions about the

behaviour of gases within the jet as those made in El-Sayed’s text. These assumptions

are bound to result in inaccuracies in calculations but were nevertheless used early on in

the design process to provide a rough estimate of operating conditions in the engine.

This text uses a different form of equation that El-Sayed to model the heat addition

during combustion. Both analyses would be carried out and their accuracy determined

from experimental results.

11

4. Conceptual Design

This section outlines the process used to determine the final layout of the project jet, the

choice of fuel, ignition system and test stand.

4.1. Valve System

The two most common valve systems found on existing pulsejet engines are grid valves

and petal valves. Grid valves are the most common type of valve used for larger engines

producing more than 100N thrust. This is because they provide the least amount of

intake flow resistance and they provide the most flexible layout on these bigger engines.

Bigger engines require a larger intake area and it is much easier and more reliable to use

several grid type valve assemblies to make up the required intake area than to design

one extremely large petal valve.

The reed valves in a grid layout are usually single valves for each intake orifice or

sometimes grouped together so that one valve covers three or four orifices. This method

of assembly is much more practical for engine maintenance. This way, if one valve

fails, it is only necessary to replace that one valve or, at the most, a group of three or

four. If one valve fails in a petal system, the entire set must be replaced.

The main disadvantage with grid valve systems is their complexity. The grid valve

systems used in large engines such as the Argus AS-014 are incredibly complex. (Figure

4.1)

Figure 4.1 Argus AS-014 Grid Valve Layout [FZG-76 Geräte-Handbuch, 1944]

12

However, the grid valve systems used on smaller engines look more like the reed valve

assemblies used at the crankcase inlet in modern two stroke engines. An example of the

reed valve assembly used in an Aprilia RS125 engine is shown in figure 4.2.

Figure 4.2 Aprilia RS125 Reed Valve Assembly

Petal valve systems, on the other hand, are much simpler to design and construct. They

consist of a flat plate which covers the front of the engine in which a radial pattern of

holes is machined. A single spring steel valve shaped like a “flower” (figure 4.3) covers

all the holes. A circular, curved, steel disk called the valve retainer is bolted to the valve

plate behind the petal valve to limit the distance which the valves can flex when open.

Figure 4.3 Petal Valve

13

The biggest disadvantage of the petal valve system is its inefficiency. Because the valve

is placed perpendicular to the incoming airflow, they produce a lot of resistance. This

limits their use to smaller pulsejets. Also, if one petal of the valve fails, the entire valve

must be replaced.

Considering both options, it was chosen to use a petal valve system for the project jet.

This type of system would allow for quicker manufacturing and would also help

incorporate a central fuel delivery point as outlined in section 4.3.

4.2. Choice of Fuel

One of the major advantages of pulsejet engines is their ability to run on most

commercially available fuels.

Many small pulsejets used for model aircraft propulsion are run on liquid fuels such as

methanol or nitro-methane. These fuels may be attractive for this purpose as they have a

high energy density and good flammability range in air. However, nitro-methane is too

expensive to be used in a larger scale engine as the fuel consumption would make it

costly to run. Methanol has a very high flammability range but also has the

disadvantage of burning with a clear flame. This could prove to be a safety hazard in a

laboratory environment.

Diesel or kerosene fuels are also a good alternative. These fuels are cheap compared to

other alternatives but they do cause problems during cold starting. These fuels need to

be vaporised prior to injection which requires the use of a heat exchanger coil. Engines

using these fuels are usually started on a more flammable fuel and then switched over to

diesel or kerosene when the engine has reached operating temperature. The use of these

fuels has the added complexity of having a secondary fuel system for the starting fuel.

Ordinary low-octane petrol has been used with some success in pulsejet engines. Petrol

is easily ignited using a spark plug which eliminates the need for a secondary fuel

system. It is also cheap and readily available. However it does need to be vaporised

before combustion which makes it unsuitable for direct injection into the combustion

chamber unless a heat exchanger coil is used.

14

The other disadvantage with using liquid fuels is the need for a fuel pump to provide the

correct fuel pressure. This adds complexity to the project. The use of a fuel pump can be

avoided if the engine is designed to be naturally aspirated. This method has the

drawback of not being throttle-able as outlined in section 4.3. The problem with fuel

pressure can be overcome if a gaseous fuel such as propane or butane is used. The gas

would be fed from the cylinder already under pressure and the fuel flow could be

regulated using a gas regulator at the cylinder exit. The use of a gaseous fuel would also

facilitate direct injection into the combustion chamber without the need for a vaporiser.

Although the gas cylinder is bulkier and heavier than a similar liquid fuel tank, this was

considered to be unimportant as the engine was to be a purely static engine.

It was decided to use propane as a fuel due to its high energy density (50 MJ/kg), ease

of cold starting by spark plug, the elimination of a fuel pump system and relatively low

cost.

4.3. Fuel Delivery

Fuel delivery to the combustion chamber can either be normally aspirated or injected.

(Figure 4.4)

Figure 4.4 Normally Aspirated (left) and Injected (right) Fuel Delivery [aardvark.co.nz, 2009]

A normally aspirated engine operates on much the same principle as the carburettor in a

car or motorcycle. The atomiser is placed in a venturi in the intake and fuel is drawn

15

from it as high-speed air passes through the venturi. Aspirated engines are simple in

construction but aspiration does pose some restrictions.

Fuel flow is very dependent on the vertical placement of the fuel tank in relation

to the atomiser.

Aspirated engines are not throttle-able as there is no method for varying fuel

flow.

The venturi must be properly designed to produce the required pressure

difference across the fuel system so fuel can flow.

Fuel injection solves the problems associated with aspiration. Although an injection

nozzle is more complex to machine, it was decided to inject the fuel in the project

engine. Injection would allow throttling of the engine and would also allow higher

flexibility of fuel use.

It was decided to inject the fuel directly into the combustion chamber behind the valve

retainer plate. A second retainer plate would be placed on the combustion chamber side

of the injection nozzle. There were several reasons behind choosing this setup.

The different valve retainer plates could be machined with different radii of

curvature. The effect of different retainer plates on valve life could then be

investigated simply by swapping them around.

The channel created between the two retainer plates would guide the fuel out

towards the point where the incoming air is moving over the tips of the retainer

plates at a higher velocity and this would aid fuel mixing.

The second retainer plate would create a secondary barrier between the valves

and the hot combustion gases and would help keep the valves cooler during

operation.

The heat absorbed by the second retainer plate during combustion would help to

preheat the fuel as it passed between the plates and this would help increase the

efficiency of combustion.

The fuel injector nozzle would also double as the central “bolt” to clamp the entire

valve head assembly together. A sketch of the assembly is shown in figure 4.5.

16

Figure 4.5 Sketch of Valve Head Design

4.4. Ignition System

The ignition system in a pulsejet engine is only required for starting to ignite the first

charge of fuel/air mixture. After the jet has achieved successful ignition and is running

correctly, the ignition system is no longer needed.

The easiest method of ignition is through a spark plug situated in the wall of the

combustion chamber. Normally a spark is created across the plug gap through the

excitation of an induction coil and then switching off the current to the main coil which

causes the magnetic field in the coil to collapse rapidly. The change in magnetic field

around a secondary coil induces a very high voltage across the coil which then jumps

the plug gap in the form of a spark.

However, instead of using an automotive coil to produce the spark, it was decided to use

a piezoelectric igniter from a gas oven. (Figure 4.6) This was an extremely simple

method. It required a push-button to be pressed repeatedly until the engine fired but it

was lightweight, cheap and it did not require any additional equipment like a battery and

separate switch.

Air

Fuel

Valve

Retainer Plate

17

Figure 4.6 Piezoelectric Oven Igniter

4.5. Test Stand

The test stand needed to fulfil the following requirements:

Securely support the jet during tests

Allow for the measurement of thrust

Support all necessary ancillary equipment such as ignition system and measuring

devices.

Be mobile enough to allow easy setup for tests.

Since the project engine was to be approximately the same size as the jet which a

previous student built, it was decided to use the same test stand design for this project

also. A CAD drawing of the test stand is shown in figure 4.7.

Figure 4.7 CAD Model of Test Stand Used With Previous Project

Push Button Earth Connection

Electrode

18

5. Theory & Design

This section details the theory used in the design, analysis and troubleshooting of the

project engine.

Due to safety concerns, it was decided that the engine in this project should produce no

more than 90N thrust. This also corresponded with the thrust limitations associated with

a petal valve design.

5.1. Jet Design

The theory governing the design of the pulsejet engine in this project was adapted from

C.E. Tharratt’s “The Propulsive Duct”. Tharratt developed his equations in the 1960s

with the imperial system of units in mind. The equations were modified to work with SI

units before being used to design the project engine.

5.1.1. Tailpipe

Tharratt proposed the following basic equation governed the basic design of the pulsejet

engine duct: = 0.00316 5.1

Where:

V = Engine Volume (cu. ft.)

L = Effective acoustic length of engine (ft.)

F = Thrust (lbf)

Manipulating this equation to take SI unit inputs produces equation 5.2:

= 0.000066 5.2

The simplest form of pulsejet is simply a straight tube of constant cross-section. It was

decided to use this as a starting point.

19

Since for a straight pipe, =

If this relationship is substituted into equation 5.2 and simplified, then a direct

relationship between thrust and cross-sectional area is established. This cross-section

area will be used as the tailpipe area and will be referred to as Ae (exhaust area) from

here on.

= 0.000066 5.3

It was decided to make use of standard seamless pipe sizes available on the market to

make the tailpipe. This would reduce the complexity of having a long welded seam

running the entire length of the pipe.

Inputting the maximum desired thrust of 90N into equation 5.3 returned a tailpipe

diameter of 87mm. The next smallest seamless mild steel pipe available on the market

was 3” Sch40 pipe. This gave an internal diameter of 78mm.

Using 3” Sch40 pipe as the basis for the design, the expected thrust was calculated by

substituting the area of the pipe back into equation 5.3. The expected thrust returned

was 72.6N.

The total length of a pulsejet engine is what determines the frequency at which it

operates according to another of Tharratts basic equations, 5.4.

= 4

5.4

There is still quite a bit of debate regarding the correct operating frequency for a given

size of jet. Therefore it was decided to look at some existing designs, their operating

frequencies and their length to diameter (L/D) ratios to determine a suitable length for

this engine. The known properties of some existing pulsejet designs are shown in table

5.1.

20

Table 5.1 Known Pulsejet Properties

Engine Static Thrust Output (N) Frequency (Hz) L/D ratio

Argus AS-014 2,200 46 9.6

Dynajet 20 260 15

By assessing the above data and considering the intended thrust output of the project

engine, it was determined that an L/D ratio of 14 would be a good starting point for the

engine. This would allow trimming of the tailpipe later on during testing if needed.

Using this ratio and the internal diameter of 3” Sch40 pipe, a total engine length of 1.1m

was calculated.

This length was substituted into equation 5.4. The operating temperature of the engine

was estimated to be 1000K approx.

= 4 ≈ √1.36 ∗ 287 ∗ 10004 ∗ 1.1 ≈ 142

This frequency falls within the expected range for a pulsejet of this size.

5.1.2. Valve Plate

Another important relationship which Tharratt developed was that which related the

intake valve area to the exhaust area. He proposed that:

= 0.23 5.5

This equation does not take into account the inefficiencies associated with different

valve layouts. It is generally assumed that a petal valve layout has an efficiency of 0.5.

Therefore the equation must be modified to allow for this. To make calculation simpler,

equation 5.5 can be modified to allow for the efficiency factor and to take an input of

tailpipe diameter rather than area:

= 0.115 5.6

= 2205

21

A “combustion chamber” is not necessary in a pulsejet engine. However, due to the

layout of a petal valve system, it is usually necessary to include a wider section which

resembles a combustion chamber at the front of the tailpipe. This wider section will be

referred to as a combustion chamber for convenience. The valve plate layout must be

designed before the dimensions of this section can be determined.

The valve plate was designed in ProEngineer by observing the following criteria and

attempting meet the required valve area while keeping the outer diameter of the orifices

as low as possible.

It was desired to keep the number of petals in the valve as low as possible so that

the probability of failure due to fatigue could be kept low.

It was also observed by studying previous designs that the maximum diameter

intake hole was 12mm to reduce deformation of the valve during the positive

pressure cycle of the engine. To try and solve this, the valve orifices had to have

a minimum distance of 12mm in one direction.

The valve plate needed to allow for 2mm valve overlap minimum around each

orifice.

Due to machining constraints, the smallest radius included in the design could be

no smaller than 3mm.

The final design, shown in figure 5.1, had 10 intake orifices and the outer diameter of

the intake orifice ring was 90mm.

5.1

To preven

from bein

which wou

and the co

determine

During his

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Figure 5.1 Intak

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Paul Schmid

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22

valve petals

al diameter

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117mm was

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Using equ

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Frequency

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in figure 5.2

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was determin

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petal valves

valves. The

5.3)

23

5.7

ned. A 30°

ermined by

des a flange

of the jet.

of the petal

operation of

ω/ωn, where

ation of the

oked in past

s a suitable

petal valve

3

7

°

y

e

l

f

e

e

t

e

e

24

Figure 5.3 Petal Valve Geometry

According to Singiresu S. Rao’s text, “Mechanical Vibrations”, = 3

Where I is the second moment of area and for a simple beam: = 12

Therefore:

= 4 5.8

If all variables in equation 5.8 are kept constant and only b is allowed to change, then it

can be shown that, as b increases, so does k. Therefore k increases with distance from

the root of the petal valve. If the petal were to be deflected through a small distance,

then the majority of bending would occur at the root where k has its smallest value.

To simplify the problem of varying k, the petal valve was modelled as a cantilever beam

of constant cross-section equal to that at the root of the petal, with a lumped mass at the

end which would represent the extra mass of the side lobes of the valve.

The value of that extra mass was found by:

Finding the mass of the side lobes

Finding the centre of gravity of that mass

Calculating the moments produced by this mass about the root

25

Then calculating an equivalent mass which would produce the same moment

about the root if it were placed at the tip of the valve.

The result is a constant-section beam with a lumped mass at its end as shown in figure

5.4 for which the natural frequency of vibration can be easily calculated.

Figure 5.4 Simplified Petal Valve Model

The equivalent mass of this model can be found using Rao’s equation: = + 0.23 5.9

The natural frequency of vibration can now easily be calculated using

=

5.10

Where k is obtained using equation 5.8 and m is calculated from equation 5.9.

In order to find the position of the centroid of the side lobes, a simple 2D CAD program

called QCad was used. The geometry of the valve was drawn and then split into the

main “beam” and up to five other simple shapes as shown in figure 5.5.

The areas

into an Ex

following

The equi

Or:

The mass

Fig

and centro

xcel spreads

equation:

ivalent mass

of the “beam

gure 5.5 Petal V

ids of these

sheet to calc

s to be place

m” was calc

Valve Geometry

e shapes we

culate the p

= ∑ed at the en

==

culated usin

y Split for Cent

ere found us

position of t

∑∑

nd of the bea

ng: =

troid Determina

sing QCad

their combi

am was then

ation

and these v

ined centroi

n calculated

26

values input

id using the

d using:

5.11

5.12

6

t

e

2

27

In order to tune the petal valves to the required natural frequency of vibration, it was

necessary to investigate the relationship between natural frequency ω, spring stiffness k,

length L and material thickness t. By combining equations 5.8 – 5.12 and simplifying,

the following equation 5.13 was obtained.

= 4 ( + 0.23 ) 5.13

By varying t and L in equations 5.8 and 5.13, it can be shown that an increase in t will

increase the natural frequency of vibration but will also increase the static stiffness by a

larger factor. ∝ ∝

If L is reduced instead, there is a smaller increase in static stiffness for the same increase

in natural frequency.

∝ 1 ∝ 1

Therefore it is more desirable to tune the valve frequency by reducing the effective

length of the valve than by increasing the thickness. Keeping the static stiffness as low

as possible is also necessary to allow the engine to produce static thrust as the valves do

not have the benefit of ram-air pressure to help open them.

5.3. Thermodynamic Analysis

The thermodynamic cycle of the pulsejet engine was analysed using theory from two

different sources. The first is Ahmed El-Sayed’s text; “Aircraft Propulsion and Gas

Turbine Engines” and the second is the Guggenheim Aeronautical Laboratory’s

reference text “Jet Propulsion”. Both methods are examined separately. Both methods

refer to conditions within the engine at certain points. These points are illustrated in the

following diagram, figure 5.6.

28

Figure 5.6 Points of Interest Within the Pulsejet Engine

5.3.1. El-Sayed (2008)

Ahmed El-Sayed idealises the process within the pulsejet engine as illustrated in the T-S

diagram in figure 5.7 below.

Figure 5.7 Ideal pulsejet cycle [El-Sayed, 2008]

Due to ram effect in flight and inefficiencies due to diffuser shape and valve system,

both the pressure and temperature at point 2 can be calculated as follows:

= 1 + − 12

5.14

= = = 1 + − 12

5.15

a 1 2 3 4

29

Where ηd is the efficiency of the diffuser and valve system and M is the flight Mach

number.

It is assumed that combustion takes place at a nearly constant volume. Therefore:

=

5.16

T03 is determined from the energy balance in the combustion chamber, equation 5.17.

+ = + 5.17

Where Cp is the specific heat capacity at constant pressure and ηb is the burner

efficiency.

The exhaust gases expand out the tailpipe to ambient pressure. This process is assumed

to be isentropic and the temperature of the exhaust gases is calculated from the

following relationship, equation 5.18:

=

5.18

The exhaust velocity and thrust are then calculated from equations 5.19 and 5.20

respectively.

= 2 1 −

5.19

= (1 + ) − 5.20

5.3.2. Guggenheim Aeronautical Laboratory (1946)

The reference text, “Jet Propulsion”, makes precisely the same assumptions as El-Sayed

up until the combustion stage. Although the assumptions about constant volume

combustion and isentropic expansion remain the same, this text proposes different

relationships to model the process of heat during combustion. This is described in

equation 5.21 below.

30

ℎ = = ( − ) = 1 1 −

5.21

5.4. Material Selection

5.4.1. Jet Body

In order to choose a suitable material for the jet body, it was necessary to first determine

the maximum pressures which could be expected within the engine during operation.

These pressures were obtained from the preliminary thermodynamic analysis in section

5.3. Also considered were pressure cycle plots obtained from existing pulsejet engines.

The analysis in section 5.3 provided a reasonable estimate for the stagnation pressure in

the combustion chamber as

P03 = 4.1 Bar

Adding in a factor of safety of approximately 2, the jet body should be capable of

withstanding maximum internal pressures of up to 8 Bar.

Comparing to existing pulsejet analysis as shown in figure 3.1 and fig 5.8, 8 Bar

pressure appears to provide a huge factor of safety. Figure 3.1 shows a peak pressure of

27 psi or 1.86 Bar and figure 5.8 shows a peak pressure of 28 psi or 1.93 Bar.

Considering that both jets are at different ends of the thrust scale with the project jet

lying between them, it seemed reasonable to assume that the actual pressures

experienced in the jet would be very similar. Therefore, by choosing the material to

withstand 8 Bar pressure, it could be ensured that the safety concerns of the university

could be comfortably met.

Since the

not a majo

steel or sta

Mild steel

Lo

Be

Be

Su

ma

45

Th

Due to th

welded-se

rupturing

material o

application

A stress a

thick-wall

78.1mm a

Figure

project jet w

or concern.

ainless steel

l has more a

ower cost an

etter machin

etter weld-ab

uperior heat

ade from st

seconds” (

his problem

he combina

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under opera

of choice a

ns.

analysis of

led cylinder

and 5.49mm

5.8 Pressure Cy

was to be a

Amateur-bu

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appeal as a p

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bility

t radiation p

ainless stee

(Beck, 2005

is reported

ation of pre

ral steel tub

ating condit

as this was

the 3” Sch

r theory. Th

m respectivel

= 39.05.49

Cycle plot in AS

a purely stat

uilt pulsejet

pulsejet mat

vailability

properties.

el should no

5) as the bo

to be elimin

essure and

bing was un

tions. A106

s designed

h40 pipe ch

he pipe has

ly. 059 = 7.1

S-014 pulsejet e

tic test engi

ts are most

terial over s

According

ot be operat

ody can ove

nated if mil

high temp

ndesirable a

6 seamless s

for use in

hosen in se

s a nomina

10 = ℎ

ngine [Bressma

ne, the total

commonly

stainless ste

to one pul

ted staticall

erheat and b

ld steel is us

perature in

as the welde

teel pipe wa

high-temp

ction 5.1.1

l diameter

ℎ

an, 1946]

al weight of

constructed

eel for sever

lsejet websi

ly for “mor

burn holes i

sed.

the engine

ed seam wa

was decided

perature, hig

was condu

and wall th

31

f the jet was

d from mild

ral reasons:

ite, engines

re than 30 -

in the steel.

e, common

as at risk of

upon as the

gh-pressure

ucted using

hickness of

s

d

s

-

.

n

f

e

e

g

f

32

According to thick-walled cylinder theory:

= − 1 +

5.22

Since the maximum stress is needed and maximum stress occurs at the outer wall, then r

= ro and equation 5.22 can be simplified to:

= 2 −

5.23

Using the dimensions of the pipe and the expected pressures then the hoop stresses were

calculated as follows:

Table 5.2 Max Hoop Stress in Jet Tube

Pressure (Bar) 8 1.93

Max Hoop Stress, σh max (MPa) 5.36 1.29

While no information was found for the yield strength of A106 steel at high

temperature, the stress values in table 5.2 were compared against information found for

several other weaker grades of carbon steel. The comparison showed that the stresses in

the jet tube were significantly lower than the yield strengths of mild steel grades which

were not designed to operate under high temperature. An example of the temperature

dependant properties of common grade 43A steel is shown in figure 5.9. From the plot,

the yield stress of 43A steel at 800°C can be approximated to ≈15Mpa.

33

Figure 5.9 Mechanical Properties of Grade 43A Steel at Elevated Temperatures [Bailey, 2009]

5.4.2. Valve Plate

The valve plate must be able to withstand the repeated impact of the valve tips up to

150-200 times per second. As well as being able to withstand this impacting, the valve

plate should also provide a certain amount of damping force to the valve tips. This

damping force should absorb some of the impact energy from the valves and thereby

reduce the amount of stress the valve tip experiences during impact. This would help to

increase the operating life of the valves. The concept of energy being absorbed by a

material during an impact was related back to strain energy theory.

“The energy stored within a material when work has been done on it is termed the strain

energy” (Hearn, 1997).

Since the work being done on the valve plate is the impact from the valve, the material

which stores the most amount of strain energy will be the best material choice for the

valve plate. Some of the kinetic energy of the valve tip will be converted to strain

energy in the valve plate material.

34

Strain energy can be expressed as:

= 2

Or:

= 2

5.24

V will be constant for a given valve plate design. σ will also be constant for a given

valve impact. If the only variable is the material of the valve plate, then:

∝ 12

A material with smaller E will result in a smaller value of U

To maximise U, aluminium with E = 70GPa was chosen for the valve plate material

over steel with E = 200GPa. The downside to using aluminium is that aluminium has a

very low surface hardness. This would most likely result in the repeated impact of the

valves damaging the surface of the valve plate and affecting the seal between the valve

plate and the valves. To avoid this, it was decided to hard-anodise the machined valve

plate. The thin layer of aluminium oxide would increase surface hardness significantly

without affecting the underlying material properties. A table showing Vickers hardness

values for different materials is included below in table 5.3 as a comparison.

Table 5.3 Material Hardness Comparison Table [Hard Anodising Ltd, 2005]

Material Vickers Hardness Number

Untreated Al 6082 100 – 120

Hard Anodised Al 6082 400 – 460

Mild Steel 200 – 220

Stainless Steel 300 – 350

35

Additionally, it was determined that an aluminium valve plate would conduct heat from

the valves quicker than steel and help keep them from overheating.

5754 aluminium alloy was chosen as the final valve plate material due to its excellent

anodising properties and local availability.

36

6. Construction

This section details the manufacturing and construction of the project engine, the

problems encountered and how they were overcome.

The majority of manufacturing of the components was carried out in the university’s

engineering workshop. Detailed engineering drawings of all components can be found

in appendix A of this report.

6.1. Jet Body

The tailpipe section of the jet body was made from a 1m length of 3” Sch40 seamless

carbon steel pipe. The nominal wall thickness of this pipe is 5.5mm, therefore, the

combustion chamber was designed to have the same wall thickness. The tailpipe was

left ~150mm too long to allow tuning of the exhaust during testing.

The combustion chamber was machined from a solid carbon steel piece to the

dimensions shown in appendix A. The finished combustion chamber was welded to one

end of the tailpipe.

To allow easy assembly and disassembly of the engine, a flange was machined from

3mm mild steel plate. The flange incorporated eight 6mm holes which were designed to

take M5 bolts to bolt the engine together. The flange was welded to the front of the

combustion chamber.

A small fitting was machined to allow the spark plug to be incorporated into the jet

body. This fitting was simply a 10mm piece of 25mm diameter round bar. A 5mm step

was machined in the piece so that the OD of the step was 18mm. The fitting was then

drilled and tapped with an internal M14x1.25 thread to take the spark plug.

A 19mm hole was drilled in the combustion chamber wall, 60mm from the front of the

engine. The spark plug fitting was inserted into this hole and welded in place. The flat

surface of the spark plug fitting provides a good surface for the plug’s crush washer to

seal against. The completed combustion chamber end of the jet body is shown in figure

6.1.

37

Figure 6.1 Combustion Chamber and Flange

6.2. Intake Diffuser

The intake diffuser for the jet was initially designed to be a simple cone rolled from

1mm mild steel sheet. However, the correct facilities to roll a cone of this size did not

exist in the university and, after an unsuccessful attempt to roll the cone in an external

workshop, the design was abandoned for that described below.

The final intake diffuser (figure 6.2) was machined from a solid block of aluminium.

The design was kept simple with the ID by the valve plate being 110mm and an internal

wall slope of no more than 7°.

A 10mm thick flange was incorporated into the design. Eight holes were drilled in the

flange and tapped M5x0.8 to match up with the holes in the combustion chamber flange.

38

Figure 6.2 Intake Diffuser

6.3. Valve Plates

Two different valve plates were manufactured. The first was as per the design described

in section 5.1.2 and the second was a modification of the same design. The second valve

plate simply extended the intake orifices towards the centre of the plate to increase the

total intake area available. This was designed as a back-up in case problems were found

regarding the original valve plate design during testing of the engine.

The two valve plates were CNC machined from 10mm thick 5754 aluminium alloy. The

OD of the valve plates were machined to the same OD of the flanges on the diffuser and

the combustion chamber. Eight 6mm holes were machined in them to match the flanges.

One 18mm hole was machined in the centre of the valve plates to allow the fuel delivery

nozzle to pass through.

Both machined valve plates then had to be polished before being sent to Marchant

Engineering, Tramore, Co. Waterford to be hard anodised. The completed valve plates

are shown in figure 6.3.

39

Figure 6.3 Anodised Valve Plates; Original (left) & Modified (right)

6.4. Valve Retainer Plates

Three different valve plates were manufactured, each with a different radius of

curvature. The largest radius of curvature was chosen so that the valve would have a

maximum tip travel of about 8mm. This was determined to be the smallest tip travel

allowable to allow the incoming air to flow unrestricted.

A second retainer plate was chosen to have a much smaller radius of curvature which

would allow the valve to open further during the intake phase. This would also increase

bending stresses in the valve petals.

The third retainer plate was given the same radius of curvature as the first but without

any flat contact area in the centre. This would allow the valve to have total flexibility

from the root. The effects of different retainer plates on valve life could then be

investigated.

The three valve retainer plates were CNC machined from mild steel bar stock and an

18mm hole drilled in the centre to allow fitting of the fuel jet. One of the completed

retainer plates is shown in figure 6.4.

40

Figure 6.4 Valve Retainer Plate

6.5. Petal Valve

The petal valve was cut from 0.006” blue spring steel sheet. The intricate shape of the

petal valve cannot be cut with a snips as the material will just split. Therefore, an

electro-chemical etching process detailed in appendix C of the report was used.

The process involved first coating the material to be etched with an electrically

insulating coating. An automotive primer was used in this case. The shape of the petal

valve was then drawn on the painted surface and the lines scribed with a sharp knife to

expose the metal underneath.

The spring steel was placed in a saturated salt/water solution so that all the lines to be

scribed were submerged. A stainless steel plate of approximately the same size was

placed in the solution also with a sponge between the two pieces of metal to avoid

contact between them.

The spring steel was connected to the positive terminal of a 12V power supply and the

stainless steel plate was connected to the negative terminal. When current was switched

on, bubbles were seen to rise from the cathode. The entire apparatus was placed under

an extractor hood and left for 40 mins approx until the spring steel appeared to have

been eaten away at the scribed lines. The petal valve could then be popped from the rest

of the material and the paint cleaned off by immersing the valve in cellulose thinners for

up to 30 mins. The valve was then ready to be used in the engine with no further

modifications.

41

The electro-chemical etching process had some drawbacks.

Care must be taken to ensure a good even coat of masking paint is applied to the

valve material. Any pinholes in the cured paint will result in pinholes being

etched in the valve. These holes render the valve useless.

The masking paint must be allowed to cure properly for at least 48 hours.

Otherwise the etching process undercuts the paint very easily and a poor surface

on the finished valve results.

The valve must not be allowed to sit in the etching solution for too long or the

process eats through weak points in the masking paint and the finished valve

will have holes in it.

Figure 4.3 shows an electro-chemically etched valve and the etching apparatus is shown

below in figure 6.5.

Figure 6.5 Electro-chemical Etching Apparatus

During testing, shim steel was used to make valves of different thicknesses. This

material was cut using a dremel tool and the burrs ground off with a grinding wheel on

the dremel tool.

42

6.6. Fuel Injection Nozzles

6.6.1. Internal Injector

The fuel injection nozzle was turned from 25mm mild steel bar stock. A 5.5mm hole

was drilled in the centre of the piece to a depth of 45mm then six radial 2.5mm were

drilled to intersect with it and form the fuel injection outlets. An internal chamfer was

cut in the inlet hole which would help produce a tight seal with the nipple on the

propane hose.

Both sides of the piece were turned down to 18mm, leaving a 5mm wide collar at the

injection holes. An M18x1.5 thread was machined on the turned down sections.

A 15mm section at the inlet end was turned down to 16.6mm and an external 3/8 BSP

thread was cut to allow the propane hose end to be threaded on. The completed internal

fuel injection nozzle is shown in figure 6.6.

6.6.2. External Injector

During testing, it was decided to move the point of injection forward into the intake

diffuser. (see section 7.2) The quickest and simplest way to do this was to make a fitting

which would screw directly onto the original nozzle’s 3/8 BSP thread.

A 75mm piece of 20mm round bar was turned down to 16.6mm diameter. A 5.5mm

hole was drilled from one end to a depth of 48mm. Six radial 2mm holes were drilled to

intersect with the larger axial hole similar to what was done with the original nozzle.

The internal chamfer was cut in the inlet also.

At the opposite end, a 5mm hole was drilled to a depth of 20mm and then tapped M6x1.

A spare brass propane hose fitting was then fixed to this end using an M6x15 wide-head

screw bolt. The new external fuel injector can be seen in figure 6.6.

43

Figure 6.6 Fuel Injection Nozzles; Internal (top) & External (bottom)

6.7. Test Stand

The test stand was constructed to the same basic design as was used for a previous

pulsejet. However, to simplify the build for preliminary testing, it was decided to omit

the bearings from the support straps and the bearing tracks on the frame. Instead, the jet

supports would be bolted directly to the uprights in the frame. This would not allow for

thrust measurement but was a secure and simple method of securing the jet until self-

sustaining could be achieved.

The individual components of the frame were cut from 30mm box-section steel and

welded together. 9mm holes were drilled 25mm from the top of each upright before

welding.

To make the supporting straps for the jet, two 25mm wide straps of 2mm thick mild

steel were bent around a section of the tailpipe. The ends were then bent up so that there

was a gap of about 25mm between them. A 9mm hole was drilled through the tabs to

allow the straps to be tightened with M8 bolts.

Two 110mm lengths of 16mm round bar were welded to the outside of each strap so

that the bars were in line with each other and normal to the curve of the strap. Four

9mm holes were drilled in the bars to match with the holes in the frame uprights. The

straps were secured to the frame using four M8x50 bolts. Figure 6.7 shows the engine

mounted in the completed test stand.

44

Figure 6.7 Engine Mounted on Test Stand

45

7. Testing & Troubleshooting

The following section details the testing of the engine, the problems encountered and

how they were overcome. This section also details the measurement techniques which

were used at the end of the project, after successful running of the engine had been

achieved.

7.1. Ignition system problems

During initial testing, it was found that the spark generated by the piezoelectric igniter

was inadequate to ignite the propane/air mixture. No form of ignition could be achieved

using this method so it was decided to upgrade the system to use a motorcycle ignition

coil and an old motorcycle battery as a power source.

A coil was purchased and wired to the battery via a push-to-make switch. The circuit

was then tested by connecting the coil lead to the spark plug. A spark was observed but

it appeared weak and unreliable. When the circuit was connected to the engine, this

spark also proved unable to ignite the fuel/air mixture in the engine.

The spark plug which was being used up to this point was an NGK BM6A plug. This

plug has a standard thread reach of 9.5mm. It was decided to replace this plug with one

with a longer reach thread. This would place the electrode further into the engine and

increase the chances of ignition. An NGK BR9EH plug was purchased as a

replacement. The replacement plug had a 19mm thread reach and also had a higher heat

rating which would allow the engine to withstand higher engine temperatures and

therefore last longer.

A 5kV power supply was connected to the spark plug as a temporary solution to the

ignition problem. This system produced a continuous spark across the plug gap. A

continuous spark is undesirable in a pulsejet engine as it can disrupt the pulsating

combustion and cause the engine to stop. It was decided to use this method anyway to

see if the engine would at least ignite with the current spark plug position. Ignition with

the continuous spark was achieved but the jet did not pulsate at all. The result of this test

is discussed in more detail in section 7.3. It was decided that the intermittent spark

46

which could be produced using an induction coil was much more desirable for pulsejet

ignition.

The motorcycle coil in the old circuit was replaced with an old-type distributor coil

from a car and a short length of silicone HT lead was purchased to provide the

connection to the plug. However, on testing, the spark was again weak and very

unreliable. The circuit was checked over with a multimeter and the impedance of the

coil and spark plug were found to be 4 kΩ each. The total resistance of 8 kΩ between

the coil and plug electrode was much too high and the HT lead and plug were replaced.

The spark plug was replaced with a non-resistor type B9ES NGK plug and the silicone

HT lead was replaced with a length of standard copper-cored spark plug wire.

The performance of the new system was found to be very satisfactory with a strong

reliable spark being produced across the plug gap each time the switch was pushed.

Although this system was adequate for ignition, it proved awkward to have to push a

button each time a spark was needed. This system meant that more people were needed

to run a test; one person to provide spark and a second to vary the fuel flow until

ignition was achieved. An automatic system would solve this problem by allowing the

operator to simply switch on the ignition circuit, vary the fuel flow until ignition was

achieved and then switch off the ignition circuit. An ideal automatic system would be

switched on using a toggle switch and then discharge the coil at preset regular intervals

to send a steady stream of sparks across the plug gap until the system was switched off

again.

After contacting the Electronic Engineering department in the university to help with

automating the circuit, two possible solutions were determined:

1. Use a 555 timer circuit with a large transistor which would act as a switch to cut

the current to the induction coil at regular intervals which would be controlled

by the 555 circuit. This had the advantage of being completely portable with all

power to the circuit being provided by the motorcycle battery. The downside

47

was that the timing of the spark was dependant on the 555 circuit and could not

be easily changed.

2. Use almost the same circuit as above but instead of using a 555 timer to control

the transistor, a signal generator would provide a square wave signal to do the

same thing. This system had the advantage that the timing of the spark was

easily adjustable by varying the frequency of the output square wave on the

signal generator. The disadvantage was that the signal generator needed an A/C

power source and so the portability was reduced.

The second solution was chosen over the first as it was simpler to set up and the ease of

adjustment was attractive. The Electrical Engineering department also had such a circuit

already made up for demonstration purposes which was made available to this project

and could easily be integrated into the existing circuit.

The final circuit provided a reliable and adjustable ignition source for the pulsejet

during testing. It also allowed tests to be conducted more easily and with minimal

personnel. The final ignition setup is shown in figure 7.1. A circuit diagram can also be

seen in appendix B.

Figure 7.1 Final Ignition Circuit

Signal Generator

Battery

Ignition Coil

On/Off Switch & Transistor Circuit

48

7.2. Fuel Mixing

During the initial tests when the engine was igniting but was acting almost like a simple

propane burner (section 7.3), a video clip taken looking up the tailpipe showed that the

burning in the combustion chamber appeared over-rich and uneven. This can be seen in

a still image from the video clip in figure 7.2 below.

It was thought that the fuel may have been introduced too far into the combustion

chamber for adequate mixing of fuel/air to take place before combustion. To attempt to

solve this, a new fuel injector nozzle was machined as detailed in section 6.6.2. The new

fuel injector would be threaded in place between the original injector nozzle and the

propane hose and would move the point of injection forward into the intake diffuser.

This would give the fuel a much longer time to mix with the air as it passed through the

intake orifices and over the valve tips.

The new injector nozzle proved to be very effective. The engine was never tested with

the old injector nozzle after the valve frequency tuning had allowed the engine to

operate correctly as the performance of the engine with the new fuel nozzle was

significantly improved. There was no evidence of inadequate mixing with the new

nozzle.

Figure 7.2 Uneven Burning in the Combustion Chamber (left) & Burning With New Nozzle Fitted (right)

49

7.3. Valve Frequency Ratio Tuning

The engine test using the 5kV power supply to provide spark resulted in ignition of the

fuel/air mixture at a certain fuel pressure setting. The engine would not resonate and the

sound of burning was very low. If gas flow was decreased, the burning would stop and

if gas flow was increased, yellow flames would appear from the tailpipe. This led to the

conclusion that the continuous spark had set up a standing flame front inside the engine

which would only sustain at a certain fuel/air setting. The engine was acting as a simple

propane burner. It was this conclusion that led to the desire to create the intermittent

spark ignition system detailed in section 7.1.

However, the new improved ignition system did not improve the quality of burning in

the engine. Even with the sparking frequency turned down to under 0.5Hz, the engine

would still ignite the fuel/air mixture in the same manner as before. With the sparking

frequency that low, it ruled out that the problem was a standing flame front being set up

in the engine.

Further visual comparison of the movement of the petal valves before and after ignition

concluded that the engine was taking in air by itself and was therefore attempting to

resonate.

Since the tailpipe had been left oversized, the excess length was trimmed back to the

designed length of 1.1m and the test was run again. The change in length did not affect

the quality of burning in the engine at all.

When comparing the project engine to the previous engine which had been built in the

university, it was noticed that the basic jet body dimensions were almost identical. The

previous engine had achieved resonant combustion, albeit with an external supply of air.

The only major difference in design was the valve plate and petal valves. This detail,

coupled with the failed test following the length reduction, prompted an investigation

into the vibration of the petal valves.

50

In Part II of “The Propulsive Duct”, C.E. Tharratt explains how a mechanical reed valve

made up of two identical metal reeds sandwiched together provides “added stiffness

whilst retaining, as closely as possible, the response characteristics of a single metal

reed.” (Tharratt, 1965)

In order to narrow down the problem, the engine was tested using a double set of 0.006”

petal valves in place of one. This would increase static stiffness of the valves but keep

the natural frequency of vibration as close as possible to that of a single petal valve.

Using the double valve setup, the engine ran almost exactly the same way as it had in

previous tests with a single 0.006” valve. The burning characteristics were very similar

but the engine required a much higher air supply to be started and sustain burning.

These results suggested that successful resonant combustion was reliant on the natural

frequency of vibration of the petal valves.

The theory necessary to calculate the natural frequency of the petal valves is detailed in

section 5.2. An attempt was made to theoretically plot the response of a petal valve to

the forcing frequency of the jet with varying frequency ratios. However, the analysis

was regarded inconclusive due to the following reasons:

The motion of the valve cannot be modelled as a simple spring/mass system

without damping. This is due to the effect of the valve plate damping out

one-half of the valves motion. This means that the momentum of the valve

does not carry through from one cycle to the next and therefore renders

conventional modelling inaccurate.

Although the valve motion cannot be regarded as being damped, it cannot be

modelled as a damped system either. Viscous damping and coulomb

damping both restrict the motion of a spring system regardless of whether the

amplitude is positive or negative. In a reed valve system, the valve is not

restricted at all when the amplitude is positive but the valve plate does not

allow the amplitude to become negative at any time. (Figure 7.3) Essentially

the valve is returned to initial conditions [ (0) = 0; (0) = 0] before the

beginning of each negative pressure cycle.

51

Figure 7.3 Valve Motion Sign Convention (left) & Simplified Valve Motion Plot (right)

These issues prevented an accurate theoretical solution for the response of the valve to

be obtained without considerable further work. It was decided to carry out various tests,

varying the natural frequency of the valves each time and observe the results.

The next step in testing was to use a petal valve with a higher natural frequency of

vibration than the original. Using the theory in section 5.2, the original 0.006” valve was

calculated to have a natural frequency of 66Hz. If the thickness of the reed was

increased to 0.010”, the natural frequency would rise to 110Hz.

Due to the unavailability of additional sheet spring steel in Ireland, it was decided to

carry out testing using valves cut from shim steel. The shim steel valve would have the

same vibrational characteristics as a spring steel valve of equal thickness but would be

more prone to deformation. The shim steel valves would help determine whether or not

the engine would resonate with different frequency ratios.

A test was carried out using a 0.010” thick shim steel valve. The engine achieved

resonance immediately but would only sustain for 15-20 seconds. Additionally, the

engine would not sustain combustion without an external supply of air. Several

52

subsequent attempts were made to start the engine. Engine started each time but failed

to sustain for more than 10 seconds.

When the engine was disassembled following the test and the valves were examined, it

was found that one petal had been bent so much that it no longer seated against the

valve plate. (Figure 7.4) The sections of valves which covered the intake orifices were

also visually deformed from the pressure of combustion.

Figure 7.4 0.010" Deformed Shim Steel Valve Following Engine Run

The audio was extracted from a video clip of the test and analysed using Audacity

sound editor to determine the operating frequency of the engine. An operating

frequency of ~150Hz was measured from the audio file. This is very close to the

frequency of 142Hz which was estimated in section 5.1.1.

Although the engine started with a valve frequency of 110Hz, the performance was not

satisfactory. It was decided to try and run the engine with a valve frequency of roughly

double that of the previous test. The simplest method of doing this was to insert a steel

washer of a certain size behind the petal valve. This would shorten the effective length

of the valve and thereby increase the natural frequency of vibration. It was calculated

that a 47mm diameter washer would reduce the length of the valves by 9mm and

increase natural frequency to ~250Hz.

53

The engine did not fire at all with this valve in place. It was determined that the static

stiffness of the valve was too high to allow the air from the external supply to open the

valves and create an air flow through the engine. It was calculated that using one of the

0.006” petal valves with the same diameter washer would result in a natural frequency

of 150Hz but that the stiffness would be much lower. The valve was changed

immediately and another test was run. The engine ran very erratically using this setup

and was not able to sustain at a constant setting. It was determined that the frequency of

the valves was too close to the forcing frequency of the engine for normal operation to

be achieved.

To solve this problem, it was decided to make a second washer which would increase

the natural frequency of a 0.006” petal valve to 250Hz. It was calculated that a 53mm

diameter washer was needed for this. Using this setup, the engine fired and sustained for

over 1:30 minutes. The external air supply was shut off about five seconds after starting

with no noticeable difference in running. When the engine cooled and the valves

removed, visual inspection showed that the tips of many petals were broken and one

petal had cracked along its line of flexure with the washer. (Figure 7.5)

Figure 7.5 Impact and Fatigue Damage on a 0.006" Spring Steel Petal Valve

54

Due to time constraints with the project, it was decided to discontinue further valve

frequency testing and use the remaining two valves to attempt to get pressure plots and

inlet velocity data from the jet.

7.4. Valve Frequency High-Speed Camera Test

To determine the accuracy of the theoretical valve vibration model, an experiment was

conducted using a high-speed camera to measure the frequency of vibration.

A 0.010” thick shim steel valve was used for the test. The valve was set up in

front of the camera so that it was clamped between two pieces of steel at the root

of the “petal”. (Figure 7.6)

The valve was deflected by hand and released so that it vibrated naturally.

The first recording of the vibration was taken at 200 fps (frames per second) but

this was not high enough to accurately capture the vibration. A second recording

was then taken at 600 fps.

On playback, the time for five complete oscillations was noted. The period of

one oscillation could then be determined and, hence, the natural frequency. The

test recorded a frequency of 104Hz. The calculated frequency was 110Hz.

The test was run again with the valve length shortened by 9mm. This was

calculated to have a frequency of 250Hz.

The vibration was first recorded at 600 fps but it was not high enough to

accurately capture the motion. The recording speed was increased to 1500 fps

and the natural frequency determined the same way as the first test.

The recorded frequency was 227Hz. The calculated frequency was 250Hz.

The experimental values of natural frequency corresponded relatively closely to the

calculated values. This verified the theoretical model.

55

Figure 7.6 High-Speed Camera Experiment Setup

7.5. Pressure Cycle Data Collection

To obtain pressure cycle plots within the engine, a high-temperature pressure transducer

was fitted to the engine. The pressure transducer which was used was a Kistler 4045A5

with a cooling adapter.

Two ½ BSP sleeves were purchased to fit the transducer to the engine. These sleeves

were welded to the engine at positions 55mm and 1075mm from the front of the engine.

The transducer was connected to a laptop computer via a Handyscope to collect and

store the data. The water for the cooling adapter was supplied by a 12V pump from a car

windscreen wiper system. The pump was powered directly from the same battery which

powered the ignition system.

Since only one transducer was available for testing, the pressure readings from both

points had to be taken from two separate tests. In order to keep the data as consistent as

possible, the first test was started as normal but then the fuel was cut off via the main

High-Speed Camera Petal Valve

56

valve on the propane tank. By leaving the setting on the regulator, a consistent fuel flow

into the engine could be ensured.

The tests were carried out using one 0.006” petal valve. The valve was one which had

not been etched properly. When the engine did not sustain without air, it was put down

to the defects in the valve. However, due to shortage of valves, the test was carried out

anyway with the external air supply.

The data from the transducer was recorded for the forward measurement position. The

engine was then stopped and the transducer was moved to the rear measurement

position. The engine was restarted and the transducer data recorded. Shortly after

recording the last set of data, the valves failed and the engine ceased to run. Figure 7.7

shows the equipment set up for pressure data collection.

Figure 7.7 Equipment Set Up For Pressure Data Collection

Transducer Power Supply

Transducer

Cooling Pump Cooling Water Reservoir

57

8. Results

This section displays the results of the experimental data acquired during testing of the

engine.

The following plot (figure 8.1) of pressure vs. time was obtained for the front end of the

engine:

Figure 8.1 55mm Position Pressure/Time Plot

The plot displays the characteristic oscillating pressure cycles which occur at the front

of a pulsejet engine. By analysing the plot, a burning frequency of 160Hz was

calculated.

A pressure/time plot was also obtained for a position just 25mm from the end of the

tailpipe. This plot is displayed in figure 8.2.

‐0.1

0.4

0.9

1.4

1.9

2.4

0 0.01 0.02 0.03 0.04 0.05

Abs Pressure (Bar)

Time (s)

58

Figure 8.2 1075mm Position Pressure/Time Plot

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05

Abs Pressure (Bar)

Time (s)

59

9. Discussion

9.1. Jet Design

This project has shown that a pulsejet engine can be designed using a set of simple

equations. The equations derived by C.E. Tharratt do allow the basic dimensions of a

pulsejet engine to be determined “on the back of an envelope” (Tharratt, 1965).

However, very little emphasis is placed of the design of the intake valve system. Little

or no research has been carried out to accurately determine the response of a mechanical

spring valve to a forcing frequency. This response was determined to be a crucial aspect

of the correct operation of a pulsejet engine. For an engine to achieve static thrust, the

correct relationship between the frequency of operation of the engine and the natural

frequency of the reed valves must be determined. The static stiffness of the valves must

also be correct to allow the valves to open under static conditions.

9.2. Petal Valve Vibration Theory

The theoretical model for determining the natural frequency of vibration of the petal

valves was verified by capturing the vibration of the valve in front of a high-speed

camera. However, as the length of the valve was reduced, the error in calculations

appeared to increase. This may have been an error in the position where the valve was

clamped. Section 5.2 explains how natural frequency is inversely proportional to L3. If

the valve position in the clamp was even slightly off, it would result in a relatively large

error in natural frequency reading.

9.3. Valve Life

The operating life of the petal valves used in the project engine was extremely low. The

longest continuous engine run lasted for only two minutes. After the engine runs the

valves were found to have suffered severe impact damage and also fatigue damage at

the valve root.

60

Fatigue cracks at the valve root can easily be eliminated by machining a new curved

valve retainer plate with the correct root diameter. However, using the steel washer is

the simplest and fastest way of varying natural frequency of vibration. The washers

should be used to determine if a frequency ratio exists where valve impact damage is

minimised. A new retainer plate can then be machined to the required dimensions and

further fatigue testing can be carried out.

Impact damage did not appear to be a problem when using the shim steel valves

although the engine was not run for a long enough time to be conclusive. The major

problem with the shim steel valves was the ease in which they deformed into the intake

orifices during the combustion phase of the engine. The deformation affected the valves

ability to seal against the valve plate and the engine ceased to operate. The problem with

deformation was solved when using the spring steel valves.

It is possible that valves made with thicker spring steel will be able withstand the impact

damage for longer but failure is still inevitable. It could also be possible that annealing

the spring steel valves will increase valve life as outlined in section 3.2. To continue

testing, various thicknesses of spring steel sheet should be acquired.

9.4. Valve Response to Engine Forcing Frequency

As outlined in section 7.3, the response of the spring valve to the forcing frequency of

the engine is a complex problem. The problem cannot be solved using simple vibration

analysis. It would be very useful to be able to compute the motion of the valve. This

would allow the ideal natural frequency to be determined for a particular engine without

carrying out extensive testing.

During the course of the project, the simulation of this motion was attempted by

modelling the motion as both damped and undamped vibration. However, both these

methods failed to simulate the motion in a satisfactory manner. It is possible that a

detailed FEM analysis of the spring valve could produce more satisfactory results. The

downside is that this form of analysis is usually time consuming and it is not guaranteed

to produce an accurate result.

61

9.5. Ignition System

The importance of a reliable ignition system was realised during the early stages of

testing in this project. The ignition system is vital to the starting of the engine and

should be properly designed and tested well in advance of the first scheduled engine

test. Almost two to three weeks of testing were lost due to the failure to construct a

reliable ignition system for the engine.

9.6. Thermodynamic Analysis

Much is left to be done when it comes to modelling the thermodynamic processes

within a pulsejet engine. The theory described in section 5.3 was determined to be

inaccurate when compared to experimentally obtained results. The combustion process

in a pulsejet engine is neither a constant pressure nor a constant volume process and

therefore cannot accurately be modelled as either. The pressures anticipated were much

higher than those measured during testing.

Further testing must be done to determine which method of calculating the heat addition

from the fuel is more accurate. This can be done by obtaining exhaust velocities as well

as intake velocities and comparing experimental values to the theoretical values

obtained.

9.7. Pressure Cycle Visualisation

The pressure/time plot obtained in figure 8.1 correlates very well to those found in

literature. The peak pressures achieved in the combustion chamber area appear to be

very similar. They appear to be consistent throughout all sizes of engine. When

comparing the peak pressures experienced in the 50cm jet (figure 3.1), the Argus AS-

014 engine (figure 5.8) and the project jet (figure 8.1), they are all within 0.07 Bar of

each other. The pressure plot also allows the accurate determination of operating

frequency.

The pressure plot obtained from the tailpipe of the engine is more difficult to

understand. It is much more inconsistent than the plot obtained from the front of the

62

engine. This is mainly because gas velocity is at its maximum as it exits the tailpipe.

The pressure of combustion is also still present in the tailpipe as can be seen from the

high readings relative to atmospheric pressure. There is also a very high acceleration of

gases in the final section of the tailpipe due to the operating cycle of the engine. Exhaust

gases are decelerated during the intake phase and even reverse direction as the internal

vacuum acts on them. A small amount of fresh air is also sucked into the tailpipe during

intake before being ejected back out the tailpipe following combustion of the fresh

fuel/air mixture.

These rapid changes in gas momentum coupled with the combustion pressures create

the fluctuations in static pressure experienced at the tailpipe exit.

9.8. Exhaust Velocity Determination

Unfortunately, due to equipment restrictions, it was impossible to measure the exhaust

velocity in the engine and hence calculate thrust produced.

One solution to this could be to introduce a small metal disk to the exhaust flow at the

tailpipe exit. After running the engine for a few seconds, the temperature of this disk

could be read using an infra-red thermometer. The temperature of the wall at the tailpipe

exit should also be measured. The temperature of the disk would be the stagnation

temperature and the temperature of the wall would be the static temperature. The Mach

number of the flow could then be calculated from the following equation:

= 1 + − 12

In order to be able to carry this out, it would be necessary to have access to an infra-red

thermometer which would be capable of accurately measuring temperatures in excess of

1300K.

This temperature is determined from the difference between the estimated frequency of

142Hz at 1000K and the experimentally determined frequency of 160Hz. The higher

frequency suggests that the exhaust gas temperature is considerable higher than 1000K.

If a frequency of 160Hz is inputted into equation 5.4, an exhaust gas temperature of

1269.8K is calculated.

63

10. Conclusions

A pulsejet engine was successfully designed and built using relatively simple

theory.

Successful running of the engine was achieved following a number of tests. At

the time of project completion, the engine was capable of producing static thrust

for a time of two minutes before valve failure caused the engine to cease running

The operation of the engine was successfully analysed both theoretically and

experimentally. The theoretical models available in literature were determined to

be inaccurate for pulsejet cycle prediction. Further testing will need to be carried

out to gain a better understanding of engine cycles.

The pressure cycles within the engine were investigated and found to correlate

closely to similar experimentally obtained plots which have been previously

published in literature.

In order to achieve successful operation of the engine, considerable attention

must be paid to the spring valve system in the engine and its response to the

engines forcing frequency.

The theoretical model for determining the natural frequency of vibration of petal

valves was verified experimentally using a high-speed camera test.

The correlation between petal valve material and life was investigated briefly

but no solid conclusion can be determined without further testing.

Failure to construct a reliable ignition system for the engine resulted in valuable

testing time being lost. The final ignition circuit was extremely reliable and

proved to be simple to operate and adjust.

A theoretical model to simulate the valve response to a forcing frequency would

help to determine the optimum valve natural frequency needed. Simple vibration

analysis cannot achieve this.

64

References

Reynst, F. H., (1961) “Pulsating Firing for Steam Generators”, Pulsating Combustion, Pergamon Press, New York, 1961.

Museum of Flight (2010) V-1 Flying Bomb [image online], available: http://www.museumofflight.org/FileUploads/v1.jpg [accessed 18 March 2010].

Tharratt, C. E., (1965) ‘The Propulsive Duct’, Aircraft Engineering and Aerospace Technology, 37(11), 327-337.

Tharratt, C. E., (1965) ‘The Propulsive Duct’, Aircraft Engineering and Aerospace Technology, 37(12), 359-371

Ordon, R.L.. (2006) Experimental Investigations Into The Operational Parameters Of a 50 Centimeter Class Pulsejet Engine, unpublished thesis (M.Sc.), North Carolina State University, Raleigh, NC

Curran, D. (2004) Construction and Analysis of a Pulsejet, unpublished final year report, University of Limerick.

Cornell Aeronautical Laboratory (1947) 4’ x 6” Pulsejet Engine Project, DD-420-A-6, Buffalo, New York: Cornell Aeronautical Laboratory.

Manganiello, E.J., Valerino, M.F., Breisch, J.H. (1945) Endurance tests of a 22-inch Diameter Pulsejet Engine With a Neoprene Coated Valve Grid, E5J03, Cleveland, Ohio: NACA.

Bressman, J.R. (1946) Effect of a Low-Loss Air Valve on Performance of a 22-inch Diameter Pulsejet Engine, E6E15, Cleveland, Ohio: NACA.

El-Sayed, A.F. (2008) Aircraft Propulsion and Gas Turbine Engines, Zagazig: CRC Press.

Jet Propulsion (1946), Daniel Guggenheim Aeronautical Laboratory.

D. Luft (1944), FZG-76 Geräte Handbuch, T. 2076 g.

Beck Technologies (2005) ‘Dyna-jet Pictures and Video’, [online], available: http://www.beck-technologies.com/enginedynajet.html [accessed 18 March 2010].

Rao, S.S. (1990) Mechanical Vibrations, 2nd Ed., Addison-Wesley.

65

Hearn, E.J. (1997) Mechanics of Materials Volume 1, 3rd Ed., Butterworth-Heinemann.

University of Manchester (2010) Stress-strain Data for Grade 43A Steel at Elevated Temperatures [image online], available: http://www.mace.manchester.ac.uk/project/research/structures/strucfire/materialInFire/Steel/HotRolledCarbonSteel/MPFigure1.htm [accessed 18 March 2010].

Hard Anodising Ltd. (2005) ‘Hardness Testing’, [online], available: http://www.hard-anodising.co.uk/hardness-testing.asp [accessed 18 March 2010].

Bruce Simpson (2009) Fuel Delivery [image online], available: www.aardvark.co.nz/pjet/starting.shtml [accessed 18 March 2010].

A

Appendix A –

Engineering Drawings

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

A

A

78.1

1100

117

157

100386

5.49

1/17PART 0.100

ENGINE_COMPONENTS

JET_BODY

University of Limerick

29-Sep-09Thomas Naughton

0.500.010.001

0.350SCALE A-ASECTION

0.150SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

A

A

78.1

11

117

86

2/17PART 1.000

ENGINE_COMPONENTS

COMBUSTION_CHAMBER

University of Limerick

26-Oct-09Thomas Naughton

0.500.010.001

A-ASECTION

0.750SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

127

157

71

6

3/17PART 1.000

ENGINE_COMPONENTS

CC_FLANGE

University of Limerick

23-Oct-09Thomas Naughton

0.500.010.001

Thickness: 3mm

Material: Mild Steel

1.400SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

SECT

SECT

25

10

18 12.8

5

4/17PART 3.000

ENGINE_COMPONENTS

SPARK_PLUG_COLLAR

University of Limerick

20-Jan-10Thomas Naughton

0.500.010.001

Material: Mild Steel

5.000SCALE SECT-SECTSECTION

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

A

A

15710

103

120110 85

R71

4.2

5/17PART 1.000

ENGINE_COMPONENTS

DIFFUSER

University of Limerick

25-Jan-10Thomas Naughton

0.500.010.001

Material: Aluminium

Tap M5x0.8

A-ASECTION

0.600SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

A

A

10

18 18

R3

R32.5

R45

3

18

157

10

71

6

6/17PART 1.000

ENGINE_COMPONENTS

VALVE_PLATE_ORIG

University of Limerick

29-Sep-09Thomas Naughton

0.500.010.001

Material: Hard Anodised 5754 Aluminium Alloy

SEE DETAIL A

A-ASECTION

0.800SCALE

4.000SCALE ADETAIL

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

B

B

157

10

18

18

R45

6

3

18

71

6

7/17PART 1.000

ENGINE_COMPONENTS

VALVE_PLATE_MOD

University of Limerick

29-Sep-09Thomas Naughton

0.500.010.001

Material: Hard Anodised 5754 Aluminium Alloy

SEE DETAIL B

B-BSECTION

3.000SCALE BDETAIL

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

94

18

R5

4

14.48

18

8/17PART 1.000

ENGINE_COMPONENTS

PETAL_VALVE

University of Limerick

29-Sep-09Thomas Naughton

0.500.010.001

Material: 0.006" Blue Spring Steel

2.500SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

C

C

26

4

R80

94

18

9/17PART 1.000

ENGINE_COMPONENTS

VALVE_RETAINER_L

University of Limerick

29-Sep-09Thomas Naughton

0.500.010.001

Material: Mild Steel

2.000SCALE C-CSECTION

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

D

D

26

4

R50

94

18

10/17PART 1.000

ENGINE_COMPONENTS

VALVE_RETAINER_S

University of Limerick

29-Sep-09Thomas Naughton

0.500.010.001

Material: Mild Steel

2.000SCALE D-DSECTION

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

E

E

16

4

R8094

18

11/17PART 1.000

ENGINE_COMPONENTS

VALVE_RETAINER_MOD

University of Limerick

29-Sep-09Thomas Naughton

0.500.010.001

Material: Mild Steel

2.000SCALE E-ESECTION

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

A

A

18

14

3

6

40

16.6

10

25

5.5

12

3

2.5

12/17PART 1.000

ENGINE_COMPONENTS

FUEL_JET

University of Limerick

28-Nov-09Thomas Naughton

0.500.010.001

Material: Mild Steel

Cut M18x1.25 Cut M18x1.25Cut 3/8 BSP

1.500SCALE

3.000SCALE A-ASECTION

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

A

A

16.67

75

5.512

452

5

15

13/17PART 1.000

ENGINE_COMPONENTS

FUEL_JET_NEW

University of Limerick

12-Feb-10Thomas Naughton

0.500.010.001

Tap M6x1 Cut 3/8 BSP

Material: Mild Steel

3.000SCALE A-ASECTION

1.500SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE 14/17ASSEM 1.000

ENGINE_COMPONENTS

VALVE_HEAD

University of Limerick

21-Sep-09Thomas Naughton

0.500.010.001

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE 15/17ASSEM 0.083

ENGINE_COMPONENTS

ENGINE

University of Limerick

22-Sep-10Thomas Naughton

0.500.010.001

0.300SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

90

25

9

16

100

9

115

16/17PART 0.250

ENGINE_COMPONENTS

MOUNTING_STRAPS

University of Limerick

18-Jan-10Thomas Naughton

0.500.010.001

Material: Mild Steel

1.000SCALE

0.500SCALE

GENERAL TOLERANCES UNLESS NOTED

MODELDRAWN DATE

CHECKED

APPROVED DATE

DATE DRAWING NAME

SCALE SHEET

A

B

C

D

E

F

G

1 2 3 4 5 6 7 8 9

SIZE

C

.XXX .XX ANGLES

TYPE

600

1200

200

200

200

140

9170

17/17PART 0.091

ENGINE_COMPONENTS

TEST_STAND

University of Limerick

19-Mar-10Thomas Naughton

0.500.010.001

Material: 30mm Box Section Mild Steel

0.200SCALE

B

Appendix B –

Ignition Circuit Diagram

C

-+

Dis

trib

uto

r

Coi

l

To

Sp

ark

P

lug

12V

D

Appendix C –

Electro-chemical Etching Process

Preparati

Thwietc

It i

Fo

pad

Rinedg

If ddosolrinsurligto

Painting

Thfac

Pasur

Mabe shewhpai

Onsecsecpincaume

Al48

Marking

No Th eas

ion

he metal froth no trace

ching to occ

is also impo

or best resultd. This will

nse the meges.

dilute sulfune by dippilution and

nse it underrface for pa

ghtly with 12help paint a

he type of pctor in the saint the merface. ake sure aneasier to l

eet of newhile it’s flatint runs. nce the firstcond thoroucond coat nholes left iuse holes etal. low the pa hours.

Out ow scribe thhe shape ofsier to make

om which ts of rust or

cur in unwan

ortant that th

ts scrub thel remove all

etal in very

uric acid is aing the barelift it out ar hot runniaint to adhe200 grit emadhesion.

paint and thuccess of th

etal with au

even and tlay the metwspaper ant. This avoi

t coat is drugh all-oveof paint hin the paintto be etch

int to cure

he outline off the valve e a template

the reed valr grease as nted places

he metal is k

e reed valvel traces of g

y hot water,

available the metal into at regular ining water aere to. How

mery paper. T

he manner he etching outomotive p

thorough cotal on a fland spray iids creating

ry, give it aer coat. Thehelps avoidt which canhed in the

for at leas

f the reed vacan be dra

e that can be

lve will be these will

.

keyed so th

material wgrease and an

, taking car

e metal shoa very dilu

ntervals. Wagain. This

wever if aciThis will pr

in which itoperation. primer. Thi

oating of pat t g

a e d n e

t

alve that neawn directlye traced aro

etched mucause the p

at the paint

ith a soap imny rust spot

re to hold t

ould be giveute solution.

When it’s turacid-etch

d is not avrovide a sim

t’s applied

is paint wi

int is applie

eeds to be cuy onto the und.

ust be absolpaint to lift

t can adhere

mpregnatedts.

the metal o

en an acid-e. Place the mrned a dull will provid

vailable sandmilar surface

will also b

ill adhere b

ed to the m

ut. painted me

E

lutely cleant and allow

e properly.

d steel-wool

only by the

etch. This ismetal in the

gray colorde the bestd the metale roughness

be a critical

best to the

etal. It may

etal but it’s

E

n w

l

e

s e r t l s

l

e

y

s

Anas

Whpai

Chshoof val

Etching

Etcconthe

Miand

A shosolbla

Coma

Plasur

Macanmoin to tou

SwOnbucat

Atfacprosolfro

EvandtheIf be lig

Post-etchi

On Th

n existing rethe templathen scribinint should b

heck to makould – a linmetal that lve from the

ching is carntainer thate valve mateix up a satud water. piece of

ould be uselution. It shank sheet ofonnect the aterial and tace the platre that the sake sure thn not accideove. To do the middleflow while

uching. witch on thence the powubbles shouthode plate t this stage ctors, it mayocess gets ulution. Thisom the scribventually thed when thee paint on ththe plate is seen where

ght will shin

ing Steps nce the valvhe paint can

eed valve inte for scribinng is finishbe visible atke sure thatne that doeswill make ce sheet of p

rried out int is large eerial while iurated solut

stainless (ped to act ahould be abf reed valvenegative te

the positive tes in the sascribed sidehat the twoentally toucthis, a spon. This will

e preventing

e power supwer supply

uld be seenas in the picthe salt so

y take betwunderway, as is the irobed lines. e scribed lin

e plate is rehe back surheld up to

e the etchinne through a

ve is etched,now be wa

in good conng the patte

hed, the stet the bottomt all the lin

sn’t join upcomplicate

prepared me

a plastic orenough to fit’s stood ontion of com

preferred) as a cathodbout the same material. erminal of terminal to

alt solution of the valv

o pieces of ch together nge can be allow the c

g the plates

pply to the y is switchn rising frocture. olution will

ween ten mina green or bon that has

nes will etcemoved frorface can bea lamp at t

ng is complas in the pic

, it should bashed off wi

ndition can ern. eel underne

m of the scribnes join whe

will leave athe removatal.

r glass bowfully submen edge.

mmon table

or mild stde plate in me area as

a 6-12V Do the scribed

on oppositee material f

f metal if they placed current s from

plates. ed on,

om the

l still be clnutes and anbrown sludg

been remo

ch right throm the solute seen expothis stage itlete becauseture.

be pushed ouith suitable

be used

eath the be lines. ere they a bridge al of the

l or erse

salt

teel the the

DC power sd reed valvee sides of thfaces the cat

lear. Depenn hour to ete will beginoved

ough tion,

osed. t can e the

ut from the thinners.

supply to te material. he containethode plate.

nding on a tch the valvn to form on

rest of the m

F

the cathode

er – making.

number ofe. Once then top of the

metal.

F

e

g

f e e

G

Appendix D –

Turn-it-in Originality Report Summary

H

1

1% match (student papers from 10/31/08)

Submitted to University of Adelaide

2

< 1% match (student papers from 03/18/09)

Submitted to University of Limerick

3

< 1% match (Internet from 9/12/07)

http://en.wikipedia.org

4

< 1% match (Internet)

http://naca.central.cranfield.ac.uk

5

< 1% match (Internet from 1/8/09)

http://www.journalof911studies.com

6

< 1% match (publications)

I. CHOUTAPALLI. "An experimental study of an axisymmetric turbulent pulsed air jet", Journal of Fluid Mechanics, 07/2009

7

< 1% match (publications)

J. A. C. Kentfield. "The Shrouding of Highly Loaded, Aerovalved, Pulse, Pressure-Gain Combustors", Combustion Science and Technology, 11/1/1993

8

< 1% match (Internet from 9/9/08)

http://scholar.lib.vt.edu

I

9

< 1% match (publications)

Moses, E.. "On knocking prediction in spark ignition engines", Combustion and Flame, 199505

10

< 1% match (student papers from 08/29/05)

Submitted to Embry-Riddle Aeronautical University

11

< 1% match (Internet from 5/1/08)

http://etd.lib.ncsu.edu

12

< 1% match (publications)

Eichler, J.. "Theory of relativistic ion-atom collisions", Physics Reports, 199010

13

< 1% match (student papers from 02/17/10)

Submitted to University of Florida

14

< 1% match (Internet from 11/1/09)

http://www.jod911.com

15

< 1% match (student papers from 07/03/09)

Submitted to Victoria University

16

< 1% match (student papers from 11/30/08)

Submitted to Shasta College