a report on six stroke engine

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INTRODUCTION The majority of the actual internal combustion engines, operating on different cycles

have one common feature, combustion occurring in the cylinder after each compression,

resulting in gas expansion that acts directly on the piston (work) and limited to 180

degrees of crankshaft angle.

According to its mechanical design, the six-stroke engine with external and

internal combustion and double flow is similar to the actual internal reciprocating

combustion engine. However, it differentiates itself entirely, due to its thermodynamic

cycle and a modified cylinder head with two supplementary chambers: Combustion, does

not occur within the cylinder but in the supplementary combustion chamber, does not act

immediately on the piston, and it’s duration is independent from the 180 degrees of

crankshaft rotation that occurs during the expansion of the combustion gases (work).

The combustion chamber is totally enclosed within the air-heating chamber. By

heat exchange through the glowing combustion chamber walls, air pressure in the heating

chamber increases and generate power for an a supplementary work stroke. Several

advantages result from this, one very important being the increase in thermal efficiency.

In the contemporary internal combustion engine, the necessary cooling of the combustion

chamber walls generates important calorific losses.

Types of Six-Stroke Engine

There are mainly two approaches which are followed for making a six stroke engine from

a four stroke engine which are-

First Approach

There are two additional strokes by the main piston as fifth and sixth stroke. Such type of

engines which follow this approach are-

1) Griffin Six Stroke Engine

2) Bajulaz Six Stroke Engine

3) Crower Six Stroke Engine

4) Velozeta Six Stroke Engine

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Second Approach

It uses a second opposed piston which moves at half the cyclical rate of the main piston.

Engines based on this approach are-

1) Beare Head Six Stroke Engine

2) M4 +2 Engine

In addition to these two approaches current development is on Dual Fuel Six Stroke

Engine.

Analysis Of Bajulaz Six Stroke Engine

Six-stroke engine is mainly due to the radical hybridization of two and four stroke

technology. The six-stroke engine is supplemented with two chambers, which allow

parallel function and results a full eight-event cycle: two four-event-each cycles, an

external combustion cycle and an internal combustion cycle. In the internal combustion

there is direct contact between air and the working fluid, whereas there is no direct

contact between air and the working fluid in the external combustion process. Those

events that affect the motion of the crankshaft are called dynamic events and those, which

do not effect are called static events.

Fig 1. View of a six stroke engine[1]

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Fig 2. Cross sectional view of Bajulaz Engine (stroke 1)[1]

1. Intake valve

2. Heating chamber valve

3. Combustion chamber valve

4. Exhaust valve

5. Cylinder

6. Combustion chamber

7. Air heating chamber

8. Wall of combustion chamber

9. Fuel injector

10. Heater plug

Analysis of Events

Event 1: Pure air intake in the cylinder (dynamic event).

Event 2: Pure air compression in the heating chamber.

Fig3. Stroke 2 [1]

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Events 3: Fuel injection and combustion in closed combustion chamber, without direct

action on the crankshaft (static event).

Events 4: Combustion gases expanding in the cylinder, work (dynamic event).

Fig 4. Stroke 3 [1]

Events 5: Combustion gases exhaust (dynamic event).

Fig 5. Stroke 4 [1]

Event 6: Keeping pure air pressure in closed chamber where a maximum heat exchange

occurs with the combustion chambers walls, without direct action on the crankshaft

(static event).

Event 7: Expansion of the Super heat air in the cylinder work (dynamic Event).

Fig 6. Stroke 5 [1]

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Event 8: Re-compressions of pure heated air in the combustion chamber (Dynamic

event).

Fig 7. Stroke 6 [1]

External combustion cycle: (divided in 4 events) No direct contact between the air and the heating source.

e1. (Event 1) Pure air intake in the cylinder (dynamic event).

e2. (Event 2) Compression of pure air in the heating chamber (dynamic event).

e3. (Event 3) Keeping pure air pressure in closed chamber where a maximum heat

exchange occurs with the combustion chambers walls, without direct action on the

crankshaft (static event).

e4. (Event 4) Expansion of the super heated air in the cylinder, work (dynamic event).

Internal combustion cycle: (divided in 4 events) Direct contact between the air and the heating source.

I1. (Event 5) Re-compression of pure heated air in the combustion chamber (dynamic

event)

I2. (Event 6) Fuel injection and combustion n closed combustion chamber, without direct

action on the crankshaft (static event).

I3. (Event 7) Combustion gases expanding in the cylinder, work (dynamic event).

I4. (Event 8) Combustion gases exhaust (dynamic event).

Constructional Details: The sketches shows the cylinder head equipped with both chambers and four valves of

which two are conventional (intake and exhaust). The two others are made of heavy-duty

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heat-resisting material. During the combustion and the air heating processes, the valves

could open under the pressure within the chambers. To avoid this, a piston is installed on

both valve shafts which compensate this pressure.

The combustion chambers walls are glowing when the engine is running. Their

small thickness allows heat exchange with the air-heating chamber, which is surrounding

the combustion chamber. The air-heating chamber is isolated from the cylinder head to

reduce thermal loss.

The combustion and air-heating chambers have different compression ratio. The

compression ratio is high for the heating chamber, which operates on an external cycle

and is supplied solely with pure air. On the other hand, the compression ratio is low for

the combustion chamber because of effectively increased volume, which operates on

internal combustion cycle.

The combustion of all injected fuel is insured, first, by the supply of preheated

pure air in the combustion chamber, then, by the glowing walls of the chamber, which

acts as multiple spark plugs. In order to facilitate cold starts, the combustion chamber is

fitted with a heater plug (glow plug). In contrast to a diesel engine, which requires a

heavy construction, this multi-fuel engine, which can also use diesel fuel, may be built in

a much lighter fashion than that of a gas engine, especially in the case of all moving

parts.

As well as regulating the intake and exhaust strokes, the valves of the heating and

the combustion chambers allow significantly additional adjustments for improving

efficiency and reducing noise.

Working

1st stroke: The inlet valve (1) is kept open. Due to cranking, the piston moves

downward which results in the formation of a pressure difference due to which pure air

enters the cylinder (5). The crankshaft completely rotates for half cycle.

2nd

stroke: The inlet valve closes and the heating chamber valve (2) opens. The

piston moves upwards due to cranking, forcing the pure air into heating chamber (7). The

air at this stage is converted to high pressure. The fuel is injected in the combustion

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chamber and the fuel is ignited as shown the figure (initially compressed air is present in

the combustion chamber which results in the formation of fuel air mixture). Part of the

heat evolved will pass through the wall of the combustion chamber (8) and it heats up the

compressed air present in the air heating chamber. The crankshaft completes another half

cycle rotation in the 2nd stroke. At the end of 2 strokes the crankshaft will rotate 1

complete cycle.

3rd

stroke (1st power stroke): The combustion chamber valve (3) opens and the

gases of combustion enter the cylinder (5). This pushes the piston downward and hence

is known as the power stroke. The crankshaft rotates for a half cycle. It should be noted

that the air in the heating chamber is continuously heated and this results in further

increase of pressure.

4th

stroke (exhaust stroke): The exhaust valve (4) opens. The piston moves

upwards and the exhaust gases are removed via this valve. The crankshaft rotates another

half cycle. At this stage the crankshaft completes 2 full cycles. In this stroke, less amount

of heat energy is expelled out when compared to the 4 stroke ICE as this heat has already

been used to heat the air at high pressure in the air heating chamber (7).

5th

stroke (2nd power stroke): The heating chamber valve opens and the pure air

now at high pressure and high temperature enters the cylinder as shown in the figure

which does work on the piston and hence it moves downwards resulting in the 2nd

power

stroke. The crankshaft completes another half cycle.

6th

stroke: Finally the combustion chamber valve (3) opens the piston moves upwards

forcing the pure air into the combustion chamber which will be used as air for the fuel-air

mixture in the 3rd stroke or the first power stroke. The crankshaft will complete 3 full

cycles at the end of the 6th

stroke. Hence fuel is injected once every in 3 cycles of the

crankshaft whereas in a 4 stroke ICE fuel is injected once in every 2 cycles.

Graphical Representation:

Following is the graphical representation of the six strokes in a cycle. The crankshaft

rotates a total of 1080o in 1 complete cycle. The six strokes are divided into 8 events

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which are internally classified into 2 categories i.e. Static event: event occurs without the

movement of piston, Dynamic event: event which occurs with the movement of piston.

Fig 8. Six stroke engine cycle diagram [2]

Analysis of Beare Head Six Stroke Engine: This engine simply replaces the conventional Four Stroke Engines Cylinder Head. The

manufacturers Four Stroke bottom end remains unchanged. The Engine utilizes an

overhead short stroke Crankshaft and Piston arrangement which opens and closes inlet

and Exhaust Ports leading through the Upper Cylinder Liner. The Beare Head

Technology can be fitted to new production engines or retro-fitted via after market

replacement. The top and bottom Crankshaft are connected via a drive chain or toothed

belt. The top Crankshaft and Piston become positive power contributors to the overall

power output, thus increasing the amount of power/torque generated by up to a possible

35%, in essence, The Engine results in having Two Pistons Operating and

producing power within each cylinder. The absence of valves, springs, retainers and

guides, mean that the Engines bottom end has been freed up from laboring and is allowed

to spin up producing more power. The additional torque and power further generated by

the Top Piston/Crank of the Cylinder Head is then channeled via the connecting drive

chain to the `Bottom Crank. The net result of the Engine is Tractor type pulling torque.

Never before realized from a Four Stroke Internal Engine, the sort of steady locomotive

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type performance gained can only be likened to Steam Locomotives or Diesel Engines.

The net result is:- Power/torque increases of 35% (conservative)- Simpler and less

expensive manufacturing and tooling- Reduction of cylinder head reciprocating parts-

Lower maintenance costs due to less wearing parts (cylinder head)- Longer service

intervals possible due to lower operating temperatures recorded- Increased economy

due to the ability to operate and produce full operating power of much higher AIR to

FUEL ratios- Reduction of exhaust emissions due to less fuel being consumed and the

real prospect of meeting EURO-4 emissions standards, doing away with the catalytic

converter - Possible one piece engine block and head casting, saving more manufacturing

costs- Usable torque at as low as idle means suitability for lower RPM operation and

adaptation to CVT (Constantly Variable Transmission). The working of Beare head six

stroke engine can be understand with the help of following diagram:

Fig 9. Working of Beare Head six stroke engine[2]

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Dual Fuel Six Stroke Engine: This is the modern approach to six stroke engine which uses the combination of two

fuels.

Working:

The cycle of this engine consists of six strokes:

1. Intake stroke

2. First compression stroke

3. First combustion stroke 4. Second compression stroke

5. Second combustion stroke

6. Exhaust stroke

Fig 10. Working of Dual Fuel six stroke engine[3]

1) Intake or Suction stroke

To start with the piston is at or very near to the T.D.C., the inlet valve is open and the

exhaust valve is closed. A rotation is given to the crank by the energy from flywheel or

by a starter motor when the engine is just being started. As the piston moves from

top to bottom dead centre the rarefaction is formed inside the cylinder i.e. the pressure in

the cylinder is reduced to a value below atmospheric pressure. The pressure difference

causes the fresh air to rush in and fill the space vacated by the piston. The admission of

air continues until the inlet valve closes at B.D.C.

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2) First Compression stroke Both the valves are closed and the piston moves from bottom to top dead centre. The air

is compressed up to compression ratio that depends upon type of engine. For diesel

engines the compression ratio is 12-18 and pressure and temperature towards the end of

compression are 35-40 kgf/cm2 and 600-7000C.

3) First combustion stroke

This stroke includes combustion of first fuel (most probably diesel) and expansion of

product of combustion. The combustion of the charge commences when the piston

approaches T.D.C. Here the fuel in the form of fine spray is injected in the combustion

space. The atomization of the fuel is accomplished by air supplied. The air entering the

cylinder with fuel is so regulated that the pressure theoretically remains constant during

burning process. In airless injection process, the fuel in finely atomized form is injected

in combustion chamber. When fuel vapors raises to self ignition temperature, the

combustion of accumulated oil commences and there is sudden rise in pressure at

approximately constant volume. The combustion of fresh fuel injected into the cylinder

continues and this ignition is due to high temperature developed in engine cylinder.

However this latter combustion occurs at approximately constant pressure. Due to

expansion of gases piston moves downwards. The reciprocating motion of piston is

converted into rotary motion of crankshaft by connecting rod and crank. During

expansion the pressure drop is due to increase in volume of gases and absorption of heat

by cylinder walls.

4) Second compression stroke

Both the valves are closed and the piston moves from bottom to top. The combustion

products from the first compression stroke are recompressed and ut ilized in the

second combust ion process before the exhaust stroke. In typical diesel engine

combustion the combustion products still contains some oxygen.

5) Second combustion stroke

This stroke includes combustion of second fuel having low Cetane (Cetane number of

fuel is defined as percent volume of Cetane (C16H34) in a mixture of Cetane and alpha-

methyl-naphthalene that produces the same delay period or ignition lag as the fuel being

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tested under same operating conditions on same engine). The combustion of the charge

commences when the piston approaches to TDC. The second fuel injected into

recompressed burnt gas can be burnt in the second combustion process. In other words

combustion process of the second fuel takes place in an internal full EGR (Exhaust Gas

Recirculation) of the first combustion. This second combustion process was the special

feature of the proposed Six Stroke Diesel Engine.

6 ) Exhaust stroke

The exhaust valve begins to open when the power stroke is about to complete. A

pressure of 4-5 kgf/cm2at this instant forces about 60% of burnt gases into

the exhaust manifold at high speed. Much of the noise associated with automobile engine

is due to high exhaust velocity. The remainder of burnt gases is cleared

of the swept volume when the piston moves from TDC to BDC. During this stroke

pressure inside t he cylinder is slightly above the atmospheric value. Some of the burnt

gases are however left in the clearance space. The exhaust valve closes shortly after TDC.

The inlet valve opens slightly before the end of exhaust stroke and cylinder is ready to

receive the fresh air for new cycle. Since from the beginning of the intake stroke

the piston has made six strokes through the cylinder (Three up And Three down). In the

same period crank shaft has made three revolutions. Thus for six stroke cycle engine

there are two power strokes for every three revolutions of crank shaft.

COMPARISON OF SIX STROKE & FOUR STROKE ENGINES:

The difference between four stroke and six stroke engine on the basis of different engine

parameters are as follows:

Engine Parameters Four Stroke

Diesel Engine

Six Stroke

Diesel Engine

Engine Speed Ne [rpm] 2007 2016

Supplied combustion heat per cycle Qt

[KJ/cycle]

0.50 0.68

Supplied combustion heat per unit time Ht

[KJ/s]

8.36 7.62

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Injection quantity per cycle Mf [mg/cycle] 11.8 16

Excess air ratio λ 2.40 1.83

Intake air flow per unit time Ma [g/cycle] 6.00 4.16

Injection quantity per unit time Mf [g/sec] 0.197 0.179

Brake torque Tb [N-m] 15.52 15.28

Brake power Lb [KW] 3.26 3.24

BSFC. b [ g / KW-h] 217.9 520.3

IMEP Pi [Kgf / cm2] 5.94 4.37

Indicated torque Ti [N-m] 19.10 18.71

Indicated power Li [KW] 4.01 3.75

ISFC bi [g / KW-h ] 177.2 163.3

Table 1. Difference on the basis of engine parameters[4]

Graphical comparison

Fig 11. P-V diagrams for Otto cycle[2]

Area under the curve of a six stroke engine is more than the four stroke engine. Thus it is

clear from the graph that the work done by the 6 stroke engine is greater than the 4 stroke

engine. Fig 9 is in reference with a Petrol engine.

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Fig 12. P-V diagrams for Dual cycles of 4stroke & six stroke engines[3]

It refers to a diesel engine. The work done by six stroke engine is greater than a 4 stroke

engine for the same amount of fuel used.

Comparison On The Basis Of Valve Timing Diagram

Four Stroke Diesel

Engine

Six Stroke Diesel Engine

Engine Type DI, Single cylinder, Air cooled, OHV

Bore x Stroke [mm] 82 x 78

Displacement [cc] 412

Top Clearance [mm] 0.9

Cavity Volume [cc] 16

Compression Ratio 21

Intake Valve Open 100

bTDC 70 bTDC

Intake Valve Close 400

aBDC 450 aBDC

Exhaust Valve Open 450 bBDC 40

0 bBDC

Exhaust Valve Close 120 aTDC 3

0 aTDC

Valve Overlap 220 10

0

Table 2. Difference on the basis of valve timing [4]

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Factors Contributing To Increased Thermal Efficiency, Reduced Fuel

Consumption And Pollutant Emission

1) The heat that is evacuated during the cooling of a conventional engine’s cylinder head

is recovered in the six-stroke engine by the air heating chamber surrounding the

combustion chamber. As a result of this less heat is wasted and this increases the thermal

efficiency.

2) After intake, air is compressed in the heat ing chamber and heated

through720o of crankshaft angle, 360

o of which in closed chamber (external

combustion).

3) The transfer of heat from the very thin walls of the combustion chamber to the air

heating chambers lowers the temperature and pressure of the gases on expansion and

exhaust (internal combustion).

4) Better combustion and expansion of gases that take place over 540o

of crankshaft

rotat ion, 360° of which is in closed combust ion chamber, and 180°

for expansion.

5) The glowing combustion chamber allows the optimal burning of any fuel and calcinate

the residues.

6) Better filling of the cylinder on the intake due to the lower temperature of the cylinder

walls and the piston head.

7) Elimination of the exhaust gases crossing with fresh air on intake. In the six stroke-

engines, intake takes place on the first stroke and exhaust on the fourth stroke.

8) Large reduction in cooling power. The water pump and fan outputs are

reduced. Possibility to suppress the water cooler.

9) Less inertia due to the lightness of the moving parts .Friction losses, theoretically

higher in the six-stroke engine, are balanced by a better distribution of pressure on the

moving parts due to the work being spread over two strokes and the elimination of the

direct combustion.

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Advantages of Six Stroke Engine

The six stroke is thermodynamically more efficient because the change in volume of the

power stroke is greater than the intake stroke, the compression stroke and the Six stroke

engine is fundamentally superior to the four stroke because the head is no longer parasitic

but is a net contributor to and an integral part of the power generation within exhaust

stroke. The compression ratios can be increased because of the absent of hot spots and the

rate of change in volume during the critical combustion period is less than in a Four

stroke. The absence of valves within the combustion chamber allows considerable design

freedom. Main advantages of the six-stroke engine are-

1) Reduction in fuel consumption by at least 40%:

An operating efficiency of six stroke engine is approximately 50%, hence the large

reduction in specific consumption. The Operating efficiency of current petrol engine is of

the order of 30%. The specific power of the six-stroke engine will not be less than that of

a four-stroke petrol engine, the increase in thermal efficiency compensating for the issue

due to the two additional strokes.

2) Two expansions (work) in six strokes:

Since the work cycles occur on two strokes (3600 out of 1080

0 ) or 8% more than in a

four-stroke engine (1800 out of 720

0 ), the torque is much more even. This lead to very

smooth operation at low speed without any significant effects on consumption and the

emission of pollutants, the combustion not being affected by the engine speed. These

advantages are very important in improving the performance of car in town traffic.

3) Dramatic reduction in pollution:

Chemical, noise and thermal pollution are reduced, on the one hand, in proportion to the

reduction in specific consumption, and on the other, through the engine’s own

characteristics which will help to considerably lower HC, CO and NOX emissions.

Furthermore, it’s ability to run with fuels of vegetable origin and weakly pollutant gases

under optimum conditions, gives it qualities which will allow it to match up to the

strictest standards.

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4) Multifuel:

Multifuel par excellence, it can use the most varied fuels, of any origin (fossil or

vegetable), from diesel to L.P.G. or animal grease. The difference in inflammability or

antiknock rating does not present any problem in combustion. It’s light, standard petrol

engine construction, and the low compression ration of the combustion chamber; do not

exclude the use of diesel fuel. Methanol-petrol mixture is also recommended.

5) Cost comparable to those of a four-stroke engine:

The six-stroke engine does not require any basic modification to the existing engines. All

technological experience and production methods remain unaltered. The cost of the

modification to the cylinder head (combustion chamber and heating chamber) is balanced

by the simplification of several elements, particularly by the lightening of the moving

parts, the reduction of the cooling system, the simplification of direct injection with no

spark plug, etc .The reduction in the dimensions of the tank and it’s housing in a vehicle

are also to be taken into consideration.

6) Liquefied Petroleum Gas:

The great reduction in specific consumption should make the use of L.P.G. in mono fuel

attractive, due to the lower cost and much lower pollution emissions than those of petrol.

In addition, with the same operating range, the volume occupied by the tanks will be

equivalent to that of present tanks.

Disadvantages Or Improvements Needed In Six Stroke Engine

1) Brake power & indicated power per cycle per cylinder is comparatively lesser.

2) The six stroke engine, though very efficient and advantageous has not

been practically implemented on a large scale.

3) The engine turns out to be bulky when compared to the conventional four stroke

engine .Thus it hasn’t been used in automobiles yet.

4) The six stroke engine is quiet complex and thus it is difficult to mass produce it.

5) The perfect coordination between the four valves is quiet difficult to achieve.

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CONCLUSION There is, at this day, no wonder solution for the replacement of the internal combustion

engine. Only improvements of the current technology can help it progress within

reasonable time and financial limits. The six-stroke engine fits perfectly into this view. Its

adoption by the automobile industry would have a tremendous impact on the environment

and world economy, assuming up to 40% reduction in fuel consumption and 60% to 90%

in polluting emissions, depending on the type of the fuel being used.

An allied with the so-responsive pickup and a wide spread of usable power,

makes the bike easy to ride. You hardly need to use the gearbox, just park it in top gear

and ride. Even backing off the throttle in the middle of a turn doesn’t require hooking

down a gear — just crack it open when you’re ready and feel the front wheel start to

aviate on you. And hands-on assessment of the six-stroke leads to some in escapable

conclusions. The industry trend away from cheaper two-stroke power in favor of costlier

but cleaner four-stroke engines in Europe, Japan and South East Asia makes a concept

like the Beare head six-stroke, which offers the best of both worlds, project a strong case

towards volume manufacture.

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REFERENCES

[1]. http://www.bajulazsa.com/Site/sixstrokeexplanations.html

[2]. http://sixstroke.com/specifications.htm

[3]. http://en.wikipedia.org/wiki/Six-stroke_engine

[4]. Conklina J. C. and Szybist J. P., "A Highly Efficient Six- Stroke Internal

Combustion Engine Cycle with Water Injection for In-Cylinder Exhaust Heat Recovery",

Energy, Volume 35, Issue 4, pp. 1658-1664 (2010).

[5]. Crower B. Method and apparatus for operating an internal combustion engine. United

States patent application 20070022977; 2005.

[6]. http://mechanical-engineering.in/forum/topic/4188-six-stroke-engine/

[7]. http://www.allindianpatents.com/patents/252642