The difference between indicated power and the brake power output of an engine is the friction power.

1. MEASUREMENT
OF
FRICTION POWER
Submitted By:-
Patiwala Dishant K.

2. The performance of an engine is evaluated on
the basis of the following;
a) Specific Fuel Consumption.
b) Brake Mean EffectivePressure.
c) Specific Power Output.
d) Specific Weight.
e) Exhaust Smoke and Other Emissions.

3. Basic measurement of engine
The basic measurements to be undertaken to evaluate the performance
of an engine on almost all tests are the following:
a. Speed
b. Fuel consumption
c. Air consumption
d. Smoke density
e. Brake horse-power
f. Indicated horse power and friction horse power
g. Heat balance sheet or performance of SI and CI engine
h. Exhaust gasanalysis

4. Fuel consumption measurement
Fuel consumption is measured in two ways:
1. The fuel consumption of an engine is measured by determining the volume
flow in a given time interval and multiplying it by the specific gravity of
the fuel which should be measured occasionally to get an accurate value.
2. Another method is to measure the time required for consumption of a
given mass of fuel

5. Measurement of air consumption
 In IC engines, the satisfactory measurement of air consumption is quite
difficult because the flow is pulsating, due to the cyclic nature of the
engine and because the air a compressible fluid.
 Therefore, the simple method of using an orifice in the induction pipe is not
satisfactory since the reading will be pulsating andunreliable.
 The various methods and meters used for air flow measurement include,
a. Air box method, and
b. Viscous-flow airmeter

6. Measurement of brake power
 The brake power measurement involves the determination of the torque
and the angular speed of the engine output shaft. The torque measuring
device is called a dynamometer.
 Dynamometers can be broadly classified into two main types, power
absorption dynamometers and transmission dynamometer.

7. Types of Dynamometers
 Absorption Dynamometers
 These dynamometers measure and absorb the power output of the engine
to which they are coupled. The power absorbed is usually dissipated as
heat by some means. Example of such dynamometers is prony brake, rope
brake, hydraulic dynamometer, etc.
 Transmission Dynamometers
 In transmission dynamometers, the power is transmitted to the load
coupled to the engine after it is indicated on some type of scale. These are
also called torque-meters.

8. Prony brake dynamometer
 One of the simplest methods of measuring brake power (output) is to
attempt to stop the engine by means of a brake on the flywheel and
measure the weight which an arm attached to the brake will support,
as it tries to rotate with the flywheel.
 It consists of wooden block mounted on a flexible rope or band the
wooden block when pressed into contact with the rotating drum takes
the engine torque and the power is dissipated in frictional resistance.
Spring- loaded bolts are provided to tighten the wooden block and hence
increase the friction.

9. Prony brake dynamometer

10. Prony brake dynamometer
 The whole of the power absorbed is converted into heat and hence this type
of dynamometer must the cooled.
 The brake horsepower is given by
 BP= 2p NT
 where, T = W × l
 W being the weight applied at a radius l.

11. Measurement of friction power
 The difference between indicated power and the brake power output of
an engine is the friction power.
 Almost invariably, the difference between a good engine and a bad engine
is due to difference between their frictional losses.
 The frictional losses are ultimately dissipated to the cooling system (and
exhaust) as they appear in the form of frictional heat and this influences
the cooling capacity required. Moreover, lower friction means availability
of more brake power; hence brake specific fuel consumption is lower.

12. Morse Test
 The Morse test is applicable only to multi cylinder engines.
 In this test, the engine is first run at the required speed and the output is
measured.
 Then, one cylinder is cut out by short circuiting the spark plug or by
disconnecting the injector as the case may be.
 In this test, the engine is first run at the required speed and the output is
measured.
 Then, one cylinder is cut out by short circuiting the spark plug or by
disconnecting the injector as the case may be.

13. Indicated Power
 The power developed in the cylinder is known as Indicated Horse
Power and is designated as IP.
 The IP of an engine at a particular running condition is obtained from the
indicator diagram.
 The indicator diagram is the p-v diagram for one cycle at that load drawn
with the help of indicator fitted on the engine. The construction and use
of mechanical indicator for obtaining p-v diagram is already explained.

14. Indicated Power
 The areas, the positive loop and negative loop, are measured with the
help of a plani meter and let these be Ap and An cm2 respectively, the net
positive area is (Ap – An).
 h=(Ap-An)/L in centimetre.
 The height multiplied by spring-strength (or spring number) gives the
indicated mean effective pressure of the cycle.
 Imep=(Ap-An)*S/L

15. Indicated Power

16. Indicated Power
 Pm=Ap*Sp/L-An*Sn/L
 Sp = Spring strength used for taking p-v diagram of positive loop, (N/m2
per cm)
 Sn = Spring strength used for taking p-v diagram of negative loop, (N/m2
per cm)
 Ap = Area in Cm2 of positive loop taken with spring ofstrength Sp
 An = Area in Cm2 of positive loop taken with spring ofstrength Sn
 IP developed by the engine is given by
 IP=PmLAn/L

17. FULE CONSUNSMPTION
 Two glass vessels of 100cc and 200cc capacity are connected in between
the engine and main fuel tank through two, three-way cocks. When one is
supplying the fuel to the engine, the other is being filled. The time for
the consumption of 100 or 200cc fuel is measured with the help of stop
watch.
 A small glass tube is attached to the main fuel tank as shown in figure.
When fuel rate is to be measured, the valve is closed so that fuel is
consumed from the burette.
 The time for a known value of fuel consumption can be measured and fuel
consumption rate can be calculated.
 Fuel consumption kg/hr = Xcc X Sp. gravity of fuel
 1000 x t

18. Friction Power
 Friction power includes the frictional losses and the pumping losses.
During suction and exhaust strokes the piston must move against a
gaseous pressure and power required to do this is called the “pumping
losses”.
 The friction loss is made up of the energy loss due to friction between the
piston and cylinder walls, piston rings and cylinder walls, and between the
crank shaft and camshaft and their bearings, as well as by the loss incurred
by driving the essential accessories, such as water pump, ignition unit etc.

19. Willan’s Line Method
 This method is also known as fuel rate extrapolation method. In this
method a graph of fuel consumption (vertical axis) versus brake power
(horizontal axis) is drawn and it is extrapolated on the negative axis of
brake power.
 The intercept of the negative axis is taken as the friction power of the
engine atthat speed.
 As shown in the figure, in most of the power range the relation between
the fuel consumption and brake power is linear when speed of the engine
is held constant and this permits extrapolation. Further when the engine
does not develop power, i.e. brake power = 0,

20. Willan’s Line Method
 The main draw back of this method is the long distance to be
extrapolated from data between 5 and 40 % load towards the zero line of
the fuel input.
 The directional margin of error is rather wide because the graph is not
exactly linear.

21. Willan’s Line Method

22. Heat balance sheet
 The performance of an engine is usually studied by heat balance-sheet.
The main components of the heat balanceare:
 Heat equivalent to the effective (brake) work of the engine,
 Heat rejected to the cooling medium,
 Heat carried away from the engine with the exhaust gases, and
Unaccounted losses.

23.  The heat supplied to the engine is only in the form of fuel-heat and
that is given by
 Qs = mf X CV
 value of the fuel.
 The various ways in which heat is used up in the system isgiven by
a) Heat equivalent of BP = kW = kJ/sec. = 0 kJ/min.
b) Heat carried away by cooling water = Cpw X mw (Two– Twi) kJ/min.
 Where mw is the mass of cooling water in kg/min or kg/sec circulated
through thecooling.
c) Heat carried away by exhaust gases = mg Cpg (Tge – Ta) (kJ/min.) or
(kJ/sec).

24.  Where mg is the mass of exhaust gases in kg/min.
 Tg = Temperature of burnt gases coming out of the engine.
 Ta = Ambient Temperature.
 Cpg = Sp. Heat of exhaust gases in (kJ/kg-K)
 A part of heat is lost by convection and radiation as well as due to the
leakage of gases. Part of the power developed inside the engine is also
used to run the accessories as lubricating pump, cam shaft and water
circulating pump.
 These cannot be measured precisely and so this is known as unaccounted
‘losses’. This unaccounted heat energy is calculated by the different
between heat supplied Qs and the sum of (a) +(b) (c).
 The results of the above calculations are tabulated in a table and this table is
known as “Heat Balance Sheet”.

25. Thank
you.