Internal Combustion Engine Performance Characteristics · PDF fileInternal Combustion Engine Performance Characteristics Submitted To ... allows comparison of work output between engines

Internal Combustion Engine Performance Characteristics

Submitted To

Dr Mark Ellis

Submitted By

MD MARUFUR RAHMAN

Thermofluids and Turbomachinery

Assignment

2011-2012

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Table of Contents

1.0 Introduction: .................................................................................................................... 3

2.0 Question Section 1: ......................................................................................................... 3

2.1 Calculation and table for performance characteristics: ............................................... 3

3.0 Question Section 2: ......................................................................................................... 6

3.1 Performance characteristics Vs engine speed (rpm) Graphs:...................................... 7

3.1.1 Raw Torque Vs Engine Speed: ............................................................................ 7

3.1.2 Raw Power Vs Engine Speed: ............................................................................. 7

3.1.3 BMEP Vs Engine Speed: ..................................................................................... 8

3.1.4 SFC Vs Engine Speed: ......................................................................................... 9

3.1.5 AFR Vs Engine Speed: ........................................................................................ 9

3.1.6 Volumetric Efficiency Vs Engine Speed: .......................................................... 10

3.1.7 Brake Thermal Efficiency Vs Engine Speed: .................................................... 10

3.1.8 Exhaust Temperature Vs Engine Speed: ............................................................ 11

4.0 Question Section 3: ....................................................................................................... 11

4.1 Corrected Measured Raw Torque and Raw Power: .................................................. 11

4.1.1 Corrected Measured Raw Torque: ..................................................................... 12

4.1.2 Corrected Measured Raw Torque Vs Engine Speed Graph: ............................. 12

4.1.3 Corrected Measured Raw Power: ...................................................................... 13

4.1.4 Corrected Measured Raw Power Vs Engine Speed Graph: ............................... 13


5.1 Air Standard Cycle Efficiency: ................................................................................. 14

5.1.1 Test Engine Air Standard Cycle Efficiency: ...................................................... 14

5.1.2 Differences between Air Std Cycle efficiency and Thermal efficiency: ........... 15


6.1 Construct an Energy Balance diagram: ..................................................................... 16

4.0 Conclusion: ................................................................................................................... 17

5.0 References: .................................................................................................................... 17


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1.0 Introduction:

A single-cylinder 4-stroke SI engine was tested on an engine dynamometer at LSBU. Engine

torque, fuel flow, airflow, and exhaust gas temperature were measured at 7 different engine

speeds, all full-load (FT). However, the small internal combustion engine is extensively used

as a convenient and compact source of power such as cultivators, pumps, cement mixers and

motor cycles. [1] Here I tried to address the questionnaires directly according to the concept of

lecture notes, text books and laboratory engine performance test. Engine specification and

performance test results were given as follows:

2.0 Question Section 1:

Calculate and expand Table1 to include the following performance characteristics:

Raw Torque (Nm), raw Power (kW), BMEP (kPa), fuel mass flow rate (kg/hr), SFC (g/kWh),

air volumetric flow rate (m3/hr), air mass flow rate (kg/hr), AFR, volumetric efficiency (%),

brake thermal efficiency (arbitrary overall efficiency) (%) and exhaust temperature (degC).

2.1 Calculation and table for performance characteristics:

“In an ideal world, each engine cycle (2 rev for 4-stroke engine) would start with the cylinder

being completely full of fuel-air mixture, and once ignited burn completely to release all of the


Assignment

2011-2012

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fuel energy rapidly. The work done and thus torque would be the same each engine cycle. In

fact ideal world the same amount of torque would be produced at any engine speed.”[2] The

calculations for test one is as follows:

i) Raw Torque = 6.4 Nm;

ii) Raw Power = Torque × Speed

= 6.4 Nm× 392.70 ��

= 2.51 kW

Brake Mean Effective Pressure (BMEP) allows comparison of work output between engines

of different types and sizes.

iii) BMEP = �� (��)�� (��)×�∗(��/�) (kPa)

= �.!� ×�"� �.#! ×�"$% ×(�&'()(×*)

= 412.44× 10- Pa

= 412.44 kPa

iv) Fuel mass flow rate,

./ 012 = 4 × 5�21�67� (Kg/hr)

= 740 × :×�"$)�-× ;)(×)(

= 1.64 Kg/hr

v) Specific Fuel Consumption,

SFC = �/ <=�>�� (g/kWh)

= �.?@×�"�

�.!�

= 652.29 g/kWh

vi) Air mass flow rate,

From the test bed figure 2.6 (viscous Flow meter calibration) graphs

A∗ = B�CD�CEF = 2 − �I�JKC CLMNLC�

A∗ = B�CD�CEF /2 = 4 − �I�JKC CLMNLC�

O��6 = 195 cc

= 195× 10�? .-

= 1.95 × 10�@ .-

Speed = -P!" ?" × 2π

= 392.70 ��]

Density, 4 = SG× 4R6�

= 0.74× 1000 SM .�-

= 740 SM .�-

Where:

P = Power (kW)

./ 012= mass flow rate of fuel (g/hr)


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2011-2012

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./ R7�= 11.90 Kg/hr

vii) Air Volumetric Flow rate,

O/R7�= calibration factor × �/ TUVWTUV (m3/hr)

= 1.007× ��.#"�.�"!

= 9.95 m3/hr

viii) Air-Fuel Ratio (AFR),

AFR = �/ TUV�/ <=�>

= ��.#"�.?@

= 7.26

ix) Volumetric efficiency,

Volumetric efficiency is a measure of effectiveness of the cylinder filling process (working

fluids – air only). However, it significantly be affected by intake and exhaust system design

and engine speed.

X5�21�6�7YZ [/ TUV[�� (\�)×]∗(V��/*)

= #.#!× ;�)((�.#! ×�"$% ×(�&'()(×*) × 100%

= 45.33 %

x) Brake thermal efficiency(arbitrary overall efficiency),

X6_��R2Z `�R� ��/ <=�>×a<=�>

= �.!� ×�"� �.?@× ;�)((×@�"""×�"� × 100%

= 13.14 %

xi) Exhaust temperature,

Exhaust temperature = 450 degC

C.F = �Tb�=T>�c=� × dTb�=T>e��@dbT>e��@ × ( dbT>dTb�=T>)'*

= �"�"�"�- × (�#-e��@)(�#-e��@) × (�#-�#-)'*

= 1.007

4R7� = �TUVfd =

�."�-×�"'(".�:P×�"�)×�#-

= 1.205 Kg/m3

A∗ = B�CD�CEF = 2 − �I�JKC CLMNLC�

A∗ = B�CD�CEF /2 = 4 − �I�JKC CLMNLC�

g012 Z 42000 KJ/Kg ./ 012 = 1.64 Kg/hr


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2011-2012

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Performance Characteristics Table

Test no 1 2 3 4 5 6 7 8

Raw Torque (Nm)

6.4 7.5 10.9 10.9 11.1 10.7 9.0 9.0

Raw Power (kW)

2.51 2.83 3.77 3.43 3.14 2.24 1.41 1.32

BMEP (kPa)

412.44 483.32 702.43 702.43 715.32 689.54 579.99 579.99

Fuel mass flow rate (kg/hr)

1.64 1.58 1.88 1.81 1.57 1.07 1.04 0.98

SFC (g/kWh)

652.29 558.34 498.49 527.43 499.31 477.89 731.80 738.54

Air volumetric flow rate(m3/hr)

9.95 11.03 12.54 12.12 10.03 6.69 5.02 5.02

Air mass flow rate (kg /hr)

11.90 13.20 15 14.50 12 8 6 6

AFR

7.26 8.36 7.99 8.03 7.66 7.47 5.80 6.16

Volumetric efficiency (%)

45.33 52.38 64.93 69.05 63.49 57.14 57.14 61.22

Brake thermal efficiency

(arbitrary overall efficiency)(%)

13.14 15.35 17.20 16.25 17.17 17.94 11.71

11.61

Exhaust temperature (degC)

450 460 450 440 430 400 350 300


Plot on graphs the following performance characteristics Vs engine speed (rpm):


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2011-2012

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Raw Torque (Nm), raw Power (kW), BMEP (kPa), SFC (g/kWh), AFR, volumetric efficiency

(%), brake thermal efficiency (arbitrary overall efficiency) (%) and exhaust temperature

(degC).

3.1 Performance characteristics Vs engine speed (rpm) Graphs:

Performance characteristics Vs engine speed graph establishes performance test results.

However, the graphs also provide concise explanation of each engine test movement of

performance characteristics.

3.1.1 Raw Torque Vs Engine Speed:

The graph shows that the engine is not operated at zero speed due to problems with raw torque

variations during the cycle, lubrications and sealing combustion. However, engine speed 1400

rpm to 1500 rpm the raw torque is not changed, its remain constant. Consequently, engine

speed 2000 rpm to 2700 rpm the raw torque is increasing but it is dropped dramatically at 3000

rpm. To 3300 rpm to 3750 rpm the engine speed increasing but raw torque decreasing. In fact

graph shows a maximum raw torque of 11.1 Nm at 2700 rpm.

3.1.2 Raw Power Vs Engine Speed:

The below graph shows that engine speed 1400 rpm to 3000 rpm, the raw power is increasing

with increasing of engine speed but it is suddenly dropped at engine speed 3300 rpm.

6.00

7.00

8.00

9.00

10.00

11.00

12.00

1400 1900 2400 2900 3400 3900

Ra

w T

orq

ue

(N

m)

Engine Speed (rpm)

Raw Torque Vs Engine Speed Graph


Assignment

2011-2012

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Conversely, engine speed 3600 rpm to 3750 rpm, the engine raw power is falling down.

However, the graph shows a maximum raw power 3.77 kW at 3300 rpm.

3.1.3 BMEP Vs Engine Speed:

The Brake Mean Effective Pressure is remaining constant at engine speed 1400 rpm to 1500

rpm. At engine speed 2000 rpm to 2700 rpm, BMEP is increasing gradually but it is dropped

at 3000 rpm. The graph shows that BMEP is again raised until 3300 rpm and finally getting

down with increasing speed of engine.

1.00

1.50

2.00

2.50

3.00

3.50

4.00

1400 1900 2400 2900 3400 3900

Ra

w P

ow

er

(kW

)

Engine Speed (rpm)

Raw Power Vs Engine Speed Graph

350.00

400.00

450.00

500.00

550.00

600.00

650.00

700.00

750.00

1400 1900 2400 2900 3400 3900

BM

EP

(k

Pa

)

Engine Speed (rpm)

Raw Power Vs Engine Speed Graph


Assignment

2011-2012

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3.1.4 SFC Vs Engine Speed:

Specific Fuel Consumption is decreasing at engine speed 1400 rpm to 2000 rpm. On the other

hand if we observe from the graph the SFC is increasing at engine speed 2000 rpm to 3000

rpm, but it is dropped at 3000 rpm to 3300 rpm and again dramatically rising until engine speed

3750 rpm.

3.1.5 AFR Vs Engine Speed:

The graph illustrates an engine Air Fuel Ratio is declining at engine speed 1400 rpm to 1500

rpm. At 1500 rpm, the AFR is 5.80:1 means for every one given mass of fuel, we have 5.80

times the mass in air. Although the concept of stoichiometric mixture...that is the point where,

chemically, there are exactly enough atoms of oxygen to burn 100% of the fuel. From the graph

this point is at an air-fuel ratio of 8.36:1.

400.00

450.00

500.00

550.00

600.00

650.00

700.00

750.00

800.00

1400 1900 2400 2900 3400 3900

SFC

(g

/kW

h)

Engine Speed (rpm)

SFC Vs Engine Speed Graph

5

5.5

6

6.5

7

7.5

8

8.5

9

1400 1900 2400 2900 3400 3900

AF

R

Engine Speed (rpm)

AFR Vs Engine Speed Graph


Assignment

2011-2012

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3.1.6 Volumetric Efficiency Vs Engine Speed:

The graph represents the volumetric efficiency is decreasing at engine speed 1400 rpm to 1500

rpm. After that the engine volumetric efficiency is increasing gradually at speed 1500 rpm to

3000 rpm. However, suddenly the volumetric efficiency is getting down at speed 3000 rpm to

3750 rpm. From the graph the maximum volumetric efficiency is 69.05% at engine speed 3000

rpm and the minimum one is 45.33% at engine speed 3750 rpm.

3.1.7 Brake Thermal Efficiency Vs Engine Speed:

The graph shows that the thermal efficiency is almost same at engine speed 1400 rpm to 1500

rpm, and then it is increasing until engine speed 2000 rpm. After that the thermal efficiency is

started decreasing dramatically with increasing engine speed. If we observe from graph the

thermal efficiency is little bit increasing at engine speed 3000 rpm to 3300 rpm and then it is

dropped by rising engine speed. Conversely, the maximum brake thermal efficiency is 17.94%

at engine speed 2000 rpm and minimum one is 11.61% at engine speed 1400 rpm.

40.00

45.00

50.00

55.00

60.00

65.00

70.00

75.00

1400 1900 2400 2900 3400 3900

Vo

lum

etr

ic E

ffic

ien

cy (

%)

Engine Speed (rpm)

Volumetric Efficiency Vs Engine Speed Graph

10.00

11.00

12.00

13.00

14.00

15.00

16.00

17.00

18.00

19.00

1400 1900 2400 2900 3400 3900Bra

ke T

he

rma

l E

ffic

ien

cy (

%)

Engine Speed (rpm)

Brake Thermal Efficiency Vs Engine Speed


Assignment

2011-2012

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3.1.8 Exhaust Temperature Vs Engine Speed:

The graph represents that the exhaust temperature increases with engine speed, reaching a

maximum of 460°C at the maximum engine speed 3600 rpm, and then it is slightly dropped at

speed 3750 rpm. However, the graph shows a maximum exhaust temperature 460 degC at 3600

rpm and a minimum exhaust temperature 300 degC at 1400 rpm.


Correct the measured Torque and Power to standard conditions according to the

formulae given below. Plot on an additional graph the corrected and Raw power:

h/ i, Y��Y6k = h/ i, �i��5k l1.18 n99pk q rs t 273298 − 0.18v

4.1 Corrected Measured Raw Torque and Raw Power:

If engine tests carried out under different atmospheric conditions, a correction factor is used to

modify the actual raw torque or raw power figures obtained. However, there are many

standards (BS, DIN, SAE), and different reference conditions. On the other hand, engine raw

torque / raw power output is also affected by air charge density and by the flow conditions into

the engine. The flow conditions are affected by the Mach number (speed of charge flow relative

to speed of sound). [2]

250

300

350

400

450

500

1400 1900 2400 2900 3400 3900Ex

ha

ust

Te

mp

era

ture

(d

eg

C)

Engine Speed (rpm)

Exhaust Temperature Vs Engine Speed Graph


Assignment

2011-2012

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4.1.1 Corrected Measured Raw Torque:

sJ�wxC i, Y��Y6k = y�z sJ�wxC i, �i��5k {1.18 B##�|F }de�P-�#: − 0.18~

= 6.4 × l1.18 n 99102 q r20 t 273298 − 0.18v

= 6.4 × 0.95 Nm

= 6.1 Nm

Corrected Raw Torque Table

Test No 1 2 3 4 5 6 7 8

Engine Speed (rpm) 3750 3600 3300 3000 2700 2000 1500 1400

Raw Torque (Nm) 6.4 7.5 10.9 10.9 11.1 10.7 9.0 9.0

Corrected Torque (Nm) 6.1 7.2 10.4 10.4 10.6 10.2 8.6 8.6

4.1.2 Corrected Measured Raw Torque Vs Engine Speed Graph:

6.00

7.00

8.00

9.00

10.00

11.00

12.00

1400 1900 2400 2900 3400 3900

Torq

ue

(N

m)

Engine Speed (rpm)

Torque Vs Engine Speed Graph

Raw Torque

Corrected Torque

Standardised Pressure, p� = 99 kPa

Dry air Pressure, pk = 102 kPa

Ambient Temperature, T = 20 degC


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2011-2012

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4.1.3 Corrected Measured Raw Power:

pJzC� i, Y��Y6k = y�z pJzC� i, �i��5k l1.18 n99pk q rs t 273298 − 0.18v

= 2.51 × 10- × l1.18 n 99102 q r20 t 273298 − 0.18v

= 2.51 × 10- × 0.95

= 2.40 kW

Corrected Raw Power Table

Test No 1 2 3 4 5 6 7 8

Engine Speed (rpm) 3750 3600 3300 3000 2700 2000 1500 1400

Raw Power (kW) 2.51 2.83 3.77 3.43 3.14 2.24 1.41 1.32

Corrected Power (kW) 2.40 2.70 3.60 3.27 3.00 2.14 1.35 1.26

4.1.4 Corrected Measured Raw Power Vs Engine Speed Graph:

1.00

1.50

2.00

2.50

3.00

3.50

4.00

1400 1900 2400 2900 3400 3900

Po

we

r (k

W)

Engine Speed (rpm)

Power Vs Engine Speed Graph

Raw Power

Corrected Power

Standardised Pressure, p� = 99 kPa

Dry air Pressure, pk = 102 kPa

Ambient Temperature, T = 20 degC


Assignment

2011-2012

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Calculate the Air Standard Cycle efficiency for the test engine.

Compare the Air Standard Cycle efficiency to the Thermal (arbitrary overall) efficiency, and

explain the differences.

5.1 Air Standard Cycle Efficiency:

The Air Standard Cycle efficiency is defined as the work done in the cycle divided by the

heat input. However, by analysing the cycle it can be shown that the air standard cycle is given

by:

X�66�Z �� $;

Where:

r = is the air and fuel compression ratio.

� = is the ratio of specific heats.

However, for air � = 1.4

5.1.1 Test Engine Air Standard Cycle Efficiency:

X6�6 �� Z �� ;V �$;

= B1 − �(P.�?);.%$;F × 100%

= 54.75%

Air Standard Cycle Efficiency Calculation Table

Test No 1 2 3 4 5 6 7 8 AFR 7.26 8.36 7.99 8.03 7.66 7.47 5.80 6.16 Air Standard Cycle Efficiency (%)

XR7� �6kZ �� $;

54.75 57.23 56.45 56.54 55.71 55.26 50.50 51.68

Air Fuel Ratio, r = 7.26

Specific heat ratio in air, � = 1.4


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5.1.2 Differences between Air Std Cycle efficiency and Thermal efficiency:

We know that all of the heat generated by combustion can be converted into useful mechanical

work. But this is not possible for real testing engine.

Firstly, when some of the heat generated it always be lost in the exhaust gases. In fact this can

be established by considering the ideal cycle for reciprocating engines.

Secondly, some of the energy produced at the piston has to be used up in pumping the air into

and out of the cylinder, in overcoming mechanical friction, and in driving the engine

accessories.[3]

Figure1: Air Standard Cycle. [3] Figure2: Practical engine test cycle.[3]

Comparison table between Air Std Cycle efficiency and Thermal efficiency

Test No 1 2 3 4 5 6 7 8

Brake thermal efficiency

(arbitrary overall efficiency) (%)

13.14

15.35

17.20

16.25

17.17

17.94

11.71

11.61

Air Standard Cycle Efficiency (%)

54.75

57.23

56.45

56.54

55.71

55.26

50.50

51.68


Assignment

2011-2012

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Engine test no one having a compression ratio r of 7.26, the air standard cycle gives an ideal

efficiency 54.75%. However, this means that only 54.75% of the heat energy can be converted

into useful work and rest of being lost as heat in the exhaust. On the other hand, the thermal

(arbitrary overall) efficiency is 13.14%. In practical, the real pressure-volume cycle does not

follow air standard cycle. The arbitrary overall efficiency is very lower than air standard cycle

efficiency because of additional heat losses due to conduction through the cylinder wall. In fact

the air standard cycle flow is not isentropic. The polytrophic index is typically 1.3 rather

than1.4. That’s why specific heats are strongly dependent on temperature rather than constant

as assumed in the standard air cycle. [3]


Choose one test site on which to construct an Energy Balance diagram.

Indicate fuel energy input, Brake work output, Heat loss to coolant, Heat loss to exhaust.

Comment on your results and compare to published literature.

6.1 Construct an Energy Balance diagram:

Internal combustion engines transfer the fuel energy converted into mechanical energy by

burning a mixture of fuel and air inside a combustion chamber. However, an Energy balance

diagram is constructed for one test site of experiment.

Indicate Fuel Energy input = ./ 012 × g012 = 1.64 × �-?"" × 42000 × 10-

��12�Y

= 19.13 × 10- W

= 19.13 kW

Brake work output /brake power = 2.40 kW

Heat loss to exhaust = (./ R7� t ./ 012) × H/ �,� ,� × (s − sR )

= (11.90 t 1.64) × �-?"" × 1 × 10- × (723 − 293 ) (J/sec)

= 1.62 kW

Heat loss to coolant = ./ R7� ��(s − sR )

= 11.90× �-?"" × 1.005 × 10- × (723 − 293 )

= 1.43 kW

��=1.005 kJ/kgK


Assignment

2011-2012

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Figure3: Energy Balance diagram.

The above energy balance diagram shows that the indicate fuel energy input 19.13 kW

converted into mechanical energy. The heat energy is lost for brake power 2.40 kW, exhaust

gasses 1.62 kW and coolant 1.43kW.

4.0 Conclusion:

In this assignment I draw interest in internal combustion engine performance characteristics.

However, I also learnt the differences between air standard cycle efficiency and the brake

thermal efficiency and their relation with engine speed. On the other hand, this assignment also

helps me to think deepen in terms of heat losses in combustion chamber and so on.

5.0 References:

1. Heywood, J.B.(1988) Internal combustion engine fundamentals.USA: McGraw-hill

Ltd.

2. Ellis, D.M. (2012) Thermofluids & Turbomachinary: IC engine performance

characteristics [Pdf handout]. LSBU, 19th March.

3. Workshop Manual, (2004) TD110-TD115 test bed and instrumentation for small

engines. TQ Education and Training Ltd.

Internal Combustion Engine Performance Characteristics · PDF fileInternal Combustion Engine Performance Characteristics Submitted To ... allows comparison of work output between engines

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