1. Brainware group of Institutions Barasat
IC Engines & Gas Turbine
ME 601
(Module 11)
Dr. Shyamal Goswami
Jan – july 2016

2. Performance and testing of IC Engine (Mod. 11)
IC engines operate at various speeds and at each speed the power output is variable with one maximum value. While developing an IC engine it is required to take in consideration all the parameters affecting the engines design and performance. There are enormous parameters so it becomes difficult to account them while designing an engine. So it becomes necessary to conduct tests on the engine and determine the measures to be taken to improve the engines performance.

3. Performance and testing of IC Engine (Mod. 11)
Performance parameters
Measurement of speed, torque, fuel consumption
Determination of IHP, BHP, FHP, specific fuel consumption
Determination of indicated thermal efficiency, brake thermal efficiency and mechanical efficiency
Plot of efficiency vs speed curves

4. Performance and testing of IC Engine (Mod. 11)
Performance Parameters :
Power ( Indicated / Brake / Friction )
Mechanical Efficiency
Fuel Air-Ratio
Volumetric Efficiency
Specific Output
Specific Fuel Consumption
Thermal Efficiency and Heat Balance
Exhaust Smoke and Emissions
Effective Pressure and Torque

5. Performance and testing of IC Engine (Mod. 11)
Factors considered in evaluating performance :
Maximum power or torque available at each speed within the useful range of speed
Range of power output at constant speed for stable operation of the engine. The different speeds should be selected at equal intervals within the useful speed range
Brake specific fuel consumption at each operating condition within the useful range of operation
Reliability and durability of the engine for the given range of operation

6. Performance and testing of IC Engine
Load : Ratio of power developed by the engine to the maximum usable power at the same speed
Speed : Revolutions per minute generated by the engine crankshaft. Speed of the engine is widely used in the computation of power, design and development.

7. Performance Parameters
Indicated Power : rate of doing work. It is defined as the power developed by combustion of fuel in the combustion chamber (IP). Indicated power is the net work obtained form the indicator diagram or net work produced in the cylinder
. It is given by :
  IP = IMEP . L . A. n .K / [ kW ]
where:
IMEP : is the indicated mean effective pressure [ N/m2 ]
A: is the area of the piston [m2 ]
n: is the number of power strokes (= N for two stroke and N/2 for four stroke )
N : speed in rpm
L : Length of stroke [m]
K : Number of cylinders

8. Performance Parameters
Engine Power :
Brake Power : An IC engine is used to produce mechanical power by combustion of fuel. Power is referred to as the rate at which work is done. Power is expressed as the product of force and linear velocity or product of torque and angular velocity. To measure power , torque or force and speed needs to be measured. The force or torque is measured by Dynamometer and speed by Tachometer at the crankshaft of the engine. The power developed by an engine and measured at the crank shaft is called the brake power (BP) and is given by :
BP = 2π N T /1000 kW
N speed in rpm and T torque of engine in N-m
T = R (Length of moment arm [m]) . F ( measured force [ N] )

9. The watt is a derived unit of power
The watt is a derived unit of power. One watt is the rate at which work is done when an object's velocity is held constant at one meter per second against constant opposing force of one newton.
W= j/s = N.m/s = kg. m/s2 .m/s = kg .m2/s3
Torque, moment or moment of force is the tendency of a force to rotate an object about an axis.
The magnitude of torque depends on three quantities: the force applied, the length of the lever arm connecting the axis to the point of force application, and the angle between the force vector and the lever arm τ = r . F [N.m]

10. A conversion factor may be necessary when using different units of power, torque, or angular speed. For example, if rotational speed (revolutions per time) is used in place of angular speed (radians per time), we multiply by a factor of 2π radians per revolution. In the following formulas, P is power, τ is torque and ω is rotational speed.
P [w] =τ [N.m} . 2π [ rad per rev] . ω [rev/sec]
Dividing by 60 / seconds per minute gives the following
P [w] = τ [N.m} . 2π [ rad per rev] . ω [rpm] / 60

11. Performance Parameters
Friction Power : difference between Indicated power and Brake power indicates the power loss in the mechanical components of engine(due to friction ):
FP = IP - BP
Mean effective pressure : Mean effective pressure is a parameter for comparing the performance of different engines. It is defined as the average pressure acting over piston throughout a power stroke. :

12. Performance Parameters
Mean effective Pressure and Torque :
Mean effective pressure and torque both are affected by the size of engine. A large engine produces more Torque for the same mean effective pressure. For this reason engines mean effective pressure gives indication of its displacement utilization and not torque. Power of an engine is dependent on its size so it is not possible to compare different engines based on their power or torque. Therefore Mean effective pressure is the true indication of the relative performance of different engines.

13. Performance Parameters
Mean effective pressure :
IMEP = IP / L. A. n. K
where:
IP : Indicated Power
A : Area of the piston
K : Number of Cylinders,
n: is the number of power strokes (= N for two stroke and N/2 for four stroke )
N : speed in rpm
If mean effective pressure is based on brake power then it is referred to as brake mean effective pressure(BMEP). If it is based on indicated power, it is called indicated mean effective pressure(IMEP). friction mean effective power is the difference of
FMEP = IMEP- BMEP
Torque : Mean effective pressure also has an effect on torque. Torque could be expressed by following relation :
T = IMEP A R K /2π ( force . Distance)

14. Performance Parameters
Air fuel Ratio : ratio of mass of air to mass of fuel in mixture. It effects the phenomenon of combustion and used for determining flame propagation velocity, the heat released in combustion chamber. :
A/F = ma / mf
For practice always relative fuel air ratio is defined. It is the ratio of actual fuel-air ratio to that of the stoichiometric fuel air ratio required for burning of fuel which is supplied.
Relative fuel-air ratio, : Actual fuel air ratio / stoichiometric fuel air ratio

15. Performance Parameters
. Brake specific fuel consumption :
It is defined as the amount of fuel consumed for each unit of brake power per hour . It indicates the efficiency with which the engine develops the power from fuel. it is used to compare performance of different engines.
The amount of fuel which an engine consumes is rated by its BRAKE SPECIFIC FUEL CONSUMPTION (BSFC).
f = mf / BP [ kg/kWh ]
Where mf is the mass of fuel supplied per hour .

16. Performance Parameters
Mechanical efficiency : The mechanical efficiency is defined as the ratio to the brake power to indicated power of engine :
η = BP/IP % ( also BMEP/IMEP , 100%)
Thermal efficiency and heat balance :
ratio of output to that of energy input in the form of fuel. It gives the efficiency with which the chemical energy of fuel is converted into mechanical work. It shows that all chemical energy of fuel is not converted into heat energy :
= BP / mf . CV
Where BP : Brake power, CV : calorific value of fuel and
mf : mass of fuel supplied per second

17. Performance Parameters
. Volumetric efficiency : ratio of actual volume inducted during suction stroke at inlet conditions to the swept volume of engine cylinder.
The amount of air taken inside the cylinder is dependent on the volumetric efficiency of an engine and hence puts a limit on the amount of fuel which can be efficiently burned and the power output. The value of volumetric efficiency of a normal engine lies between 70 to 80 percent, but for engines with forced induction it may be more than 100 percent.
η = mactual / ρa .n . Vs
Where mactual : actual mass of the air inducted
ρa : density of air
n : N for two stroke and N/2 for four stroke
N : engine rpm
Vs : Swept volume

18. Performance Parameters
Exhaust emissions : These involve three regulated emissions of CO, HC and NO For CI engines, additional emissions of PM and smoke exist. These all emissions need to be minimized.

19. While developing an IC engine it is required to take in consideration all the parameters affecting the engines design and performance. There are enormous parameters so it becomes difficult to account them while designing an engine. So it becomes necessary to conduct tests on the engine and determine the measures to be taken to improve the engines performance.

20. Measurement and testing
Speed measurement : Speed of engine is the time rate of revolutions of the crankshaft measured in rpm. Measurement of speed is essential for calculation of power and torque of the engine. The best method of measuring speed is to count the number of revolutions in a given time. This gives an accurate measurement of speed.
Measured by contact and non contact type instruments
Contact type : Tachometer, revolutions counter, tachogenerators
Non contact type : Stroboscope, photoelectric tachometer , optical encoders.
Mechanical and electrical tachometer are effected by temperature variation and are not very exact. For accurate measurement, magnetic pickup placed near a toothed wheel coupled to the engine shaft can be used,. This produces pulse for every revolution and a pulse counter will accurately measure speed.

21. Measurement and testing
Tachometer : Centrifugal force and drag cup are commonly used . Tachometer coupled to engine shaft. The test shaft rotates the tachometer shaft which is placed between two poles of an stationary magnet. This induces eddy current in the drag cup located near the magnet. The drag cup is rotated by the torque produced by the eddy currents. The spring resists the torque. The spring movement is captured by the pointer giving the reading of the speed.

22. Measurement and testing
Stroboscope : rotating disc mounted on an engine shaft. Stroboscopic light directed on the disc. A distinctive mark is made on the shaft. The flashing frequency of the light is adjusted till the mark appears stationary. The engine speed is equal to the frequency.

23. Engine testing
Measurement of fuel consumption : can be measured on volumetric or gravimetric basis.
Volumetric method – Rota meter : Float is raised as the fuel flow rises.

24. Engine testing
A rotameter consists of a tapered tube, typically made of glass with a 'float', actually a shaped weight, inside that is pushed up by the drag force of the flow and pulled down by gravity. Drag force for a given fluid and float cross section is a function of flow speed squared only,
A higher volumetric flow rate through a given area increases flow speed and drag force, so the float will be pushed upwards. However, as the inside of the rotameter is cone shaped (widens), the area around the float through which the medium flows increases, the flow speed and drag force decrease until there is mechanical equilibrium with the float's weight.
The rising of the float is calibrated against a scale, which directly gives the fuel consumption. flow rate and flow area have a linear relationship, hence the scale is directly calibrated in terms of flow rate in Kg/hr. However , rota meter is fluid specific and has to be calibrated for each fuel separately.

25. Engine testing
Gravimetric fuel measurement : for measurement valves 1 and 2 are opened and flask is filled. The weight of the fuel is noted (W1). The valve 1 is closed and engine is supplied by opening valve 2 . The weight of the fuel left over in the flask is noted (W2).. The difference of weight in a a time duration gives the total fuel consumption rate.

26. Measurement and testing
Mean effective pressure : IP computed from measurement of forces developed in the cylinder. Pressure varies throughout the cycle – can be expressed with respect to volume or crank angle. Average pressure can be used. Piston moves between BDC and TDC. Indicated net work represented by 1234 can be effectively represented by ABCD. Pressure line CD represents a mean effective pressure for varying pressure 3-4 and line AB for 1-2. Both can be represented by a mean value Pim .
Pim . (V1 - V2 ) = Net work of cycle
Pim = (Area of the indicator diagram / length of indicator diagram ). Spring constant

27. Engine testing
Determination of IHP : gives indication regarding the conversion of chemical energy in the fuel into heat energy i.e indicates output of the engine. For obtaining indicated power, the cycle pressure must be determined as a function of cylinder volume. It is essential to measure crank angle and volume in relation to pressure. Preessure volume p – V and pressure – crank angle P - ϴ are the two types of indicator diagrams that can be obtained from an engine. Both these diagrams are mutually convertible. IP can be measured by (1) indicator diagram or (2) adding brake power and friction power
Indicators for Engines : Diaphragm type , Piston type, Electronic type, Optical type

28. Engine testing Indicator diagram :
On modern engines this diagram can be continuously taken by employing two transducers, one pressure transducer in the combustion space and other transducer on the shaft. Through the computer we can thus get on line indicated diagram and power of all cylinders.]
The area is then divided by the length of the diagram in order to obtain mean height. This mean height, when multiplied by the spring constant of the indicator mechanism, gives the indicated mean effective pressures for the cylinder. The mean effective or average pressure [IMEP] can now be used to determine the work done in the cylinder.

29. Engine testing
Indicator diagram shown below for a working cycle and for a missed cycle ( shaded – no power developed). Direction of arrows shows the path to be followed in the diagram. The sign of an area depends upon the direction in which it is traced. Shaded area represents work done in charging and discharging the cylinder i.e pumping power PP – traced in opposite direction has an opposite sign compared to the un shaded area. Un shaded area represents gross power GP. Therefore indicated power IP = GP-PP

30. Engine testing h = (A1 – A2 )/L , IMEP = h . S
Work done in one cycle = Mean Indicated Pressure x Area of the Piston x Length of stroke = IMEP . A . L
To obtain the power of this unit, it is necessary to determine the rate at which work is done, i.e. multiply work by number of power strokes in one second IP = IMEP . L . A. n

31. Engine testing Engine Indicators : indicating device consists of :
Pressure sensing device ( with preamplifier)
Device for sensing the piston displacement or the angular position of the crankpin over the complete cycle
Display device which can depict both pressure and piston displacement on paper or screen
Main types of Engine indicators :
Piston indicator
Balanced diaphragm type indicator
Electronic indicator

32. Engine testing
Determination of BHP : Brake power is defined as the power obtained at the engine crank shaft or delivered power. Brake power is measured by using a power absorption device which is coupled to the drive shaft of the engine.
The torque and the angular speed measurement of engine are involved in measurement of break power. Dynamometer is used for torque measurement. The rotor of the engine which is under state is connected to stator. Rotor moves through distance 2πR against force F. Hence work done : W = 2 π R F
The external moment or torque is equal to S . L
The moment balances the turning moment R . F i.e
S. L = R. F

33. Engine testing Therefore work done per revolution = 2π S L
Work done / minute = 2π S L N
Hence Brake power is given by :
BP = 2π N T watts
Where T – torque and N - rpm

35. Engine testing
Absorption dynamometer
It absorbs and measures output power of engine. This power is dissipated in the form of heat. e.g., prony brake, hydraulic dynamometer, rope dynamometer, eddy current dynamometer, swinging field d.c. dynamometer etc. Absorption dynamometers are ideally suited for testing petrol engines for mopeds etc. Their main advantage lies in the fact that they are self air cooled and hence additional cooling is not required. This advantage is particularly significant in case of moped engines and F.H.P. motors, which are also air cooled.

36. Engine testing
Transmission dynamometer
In this the power is transmitted to load connected to engine. Torque meter is alternative name of this dynamometer. It is usually consist of strain gauge which measures the torque by angular deformation of shaft. These dynamometers are accurate and widely used in automatic units. It is available in both electric motor and hydrostatically-driven versions, Transmission Dynamometer Test Stands are designed for automatic transmission dyno testing and for testing power shift transmissions.

37. Engine testing
Measurement of Friction Power : Difference between indicated and brake power of the engine. Internal loses two kinds – pumping and friction losses. During inlet and exhaust stroke the gaseous pressure on the piston is greater on its forward side ( underside during inlet and upper side during exhaust), hence during both strokes piston must be moved against a gaseous pressure - pumping loss. Friction loss is made up against the friction between piston and cylinder walls, piston rings and cylinder walls, crankshaft and camshaft and their bearings, loss incurred by driving the essential accessories like water pump and ignition unit.
Methods : Willan’s line, Morse test, Retardation test, measurement of indicated and brake power.

38. Engine Performance characteristics
Constructed from the data obtained during actual test run of the engine
Useful in comparing the performance of one engine from the other
At a certain speed , charge indicated per cylinder per cycle will be maximum- at this point maximum force can therefore be exerted on the piston.
Torque will also be maximum at this point
Quantity of indicated charge will decrease above this speed. However power output of the engine increases with speed due to more number of cycles are executed per unit time
Air consumption will continue to increase with increases in engine speed until some point is reached

39. Engine Performance characteristics
Relationship between air charge per cylinder, torque, air consumption and IP against speed . Maximum torque occurs at lower speed than maximum IP

40. Engine Performance characteristics
Torque, IP, BP, FP plotted against speed:
The indicated power increases with engine speed as the charge density increases and more air is inducted
At low speeds, FP is low and BP is close to IP
As speed increases FP increases rapidly
Torque reaches maximum at app. 60% of the rated rpm of the engine

41. Engine Performance characteristics
BSFC plotted against engine speed : Fuel consumption increases with engine speed
BSFC drops as the speed is increased in lower speed range
At low speeds, the heat loss to the combustion chamber walls is proportionately greater and combustion efficiency poorer resulting in higher consumption. At the high speeds FP increasing in rapid rate resulting in a slower increase in BP than in fuel consumption with a consequent increase in BSFC

42. Engine Performance characteristics
Brake thermal efficiency and mechanical efficiency against speed : Brake thermal efficiency increase with engine speed and is in the 20-30% range. The maximum brake thermal efficiency is in the middle speed range. The mechanical efficiency reduces with engine speed due to higher friction losses.

43. Engine Performance characteristics
Effect on Indicated power :
The indicated power increases with engine speed as the charge density increases and more air in inducted

44. Engine Performance characteristics
Effect of engine speed on BSFC :
The brake specfic fuel consumption increases with increasing engine speed due to higher friction losses.

45. Engine Performance characteristics
Effect of engine speed on IMEP and torque :
The IMEP reduces with increasing engine speed. The IMEP reduction is due to higher friction losses and reduced volumetric efficiency at high speeds. The torque also reduces due to the same reason.

46. Engine Performance characteristics

47. Engine Performance characteristics

48. Performace characteristics