The document discusses key metrics for evaluating internal combustion engine performance: 1) Indicated power, mean effective pressure, brake power, mechanical efficiency, specific fuel consumption, and thermal efficiency are the basic measurements. 2) Indicated power is the total power developed by combustion in the cylinder, while brake power is the power available at the crankshaft. 3) Mechanical efficiency is the ratio of brake power to indicated power, and is always less than 1 due to friction losses within the engine.

1. Name :- Meet Shah (51)
Akshay Mahida (20)

2. • The performance of I.C.Engine depends on how
effectively the engine is converting the supplied
chemical energy to mechanical energy.
• It is an engineering term that is used to describe
the fuel efficiency of an engine design with respect
to thrust output.

3.  The basic measurements to be undertaken to evaluate the
performance of an engine are :-
 1) Indicated power.
 2) Mean effective pressure.
 3) Brake power.
 4) Mechanical efficiency.
 5) Specific fuel consumption.
 6) Thermal efficiency.
 7) Heat balance sheet.
 8) Volumetric efficiency.
 9) Air fuel ratio.

4.  The total power developed by combustion of fuel in the
combustion chamber of an engine is known as Indicated
power (IP).
 IP of an engine at a particular running condition is obtained
from the indicator diagram.
IP= PmLAn/60 watt
Pm = indicated mean effective pressure.
L = length of stroke.
A = cross sectional area of piston.
n = number of power stroke.
=N (for two stroke)
=N/2 ( for four stroke)

5.  Mean effective pressure is defined as hypothetical
pressure which is thought to be acting on the piston
throughout the power stroke.
 If it is based on i.p , it is known as indicated mean
effective pressure (Pmi or Imep).
 If it is based on b.p , it is known as brake mean
effective pressure (Bmep or Pmb).

6.  The indicator piston takes up the internal pressure change of
the engine cylinder which is balanced with the spring via the
connecting rod.
 The piston displacement is transformed and magnified
through a precision link mechanism to the metal stylus at the
lever top to draw an indicator diagram on the paper wrapped
on the recording drum.
 The drum movement is picked up in connection with the
engine piston movement, and transferred by means of a cord
and the cross head. The spring used should correspond to the
maximum engine output.

8. • The brake power of an IC Engine is the power available
at the crankshaft.
• The brake power of an I.C. engine is, usually, measured
by means of a brake mechanism.
• Measurement of brake power :-
1) Brake rope dynamometer.
2) Prony brake dynamometer.

9.  The rope brake as shown in below figure is device for
measuring brake power of an engine. It consists of a number
of turns of rope wound around the rotating drum attached to
the output shaft. One side of the rope is connected to a
spring balance and the other side to a loading device.
 The power is absorbed in friction between the rope and the
drum.
 Rope brake dynamometers are cheap and can be constructed
easily but brake power can’t be measured accurately.

10. • Brake Power (BP) = (W − S) π DN/60
• Where,
D is the brake drum diameter,
W is the weight of the load ,
S is the spring balance reading ,
N is speed of engine.

11.  Mechanical Efficiency is the ratio of brake power to
indicated power of an engine.
 Mathematically, mechanical efficiency.
 Since B. P. is always less than I.P. , therefore
mechanical efficiency is always less than unity.

12.  The difference between indicated power and the brake power
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 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.

13.  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.
 Then reduction in brake power developed is measured .
 The engine is run at the required speed adjusting the throttle.
 One by one all cylinder is cut off and then brake power is
measured .
 Then graph of fuel consumption v/s b.p is drawn and if this
line is extended a negative value is obtained on X-axis .
 This is called friction loss.

14.  The efficiency of a heat engine measured by the ratio
of the work done by it to the heat supplied to it.
 Thermal efficiency are of two types :-
1) Indicated thermal efficiency.
2) Brake thermal efficiency

15.  It is the ratio of the heat equivalent to one kW hour to
the heat in the fuel per I.P. hour.
 Mathematically, indicated thermal efficiency.
Indicated thermal efficiency

16.  It is the ratio of the heat equivalent to one kW hour to
the heat in the fuel per B.P. hour.
 Mathematically, brake thermal efficiency,

17.  The performance of an engine is usually studied by
heat balance-sheet. The main components of the heat
balance are:
 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.

18.  The heat supplied to the engine is only in the form of
fuel-heat and that is given by Qs = mf X CV.
 The various ways in which heat is used up in the system is
given by
 (a) Heat equivalent of BP = kW = kJ/sec. = 0 kJ/min.
 (b) Heat carried away by cooling water = Cw X mw (t2 –
t1) kJ/min.
 Where mw is the mass of cooling water in kg/min or kg/sec
circulated through the cooling.

19.  (c) Heat carried away by exhaust gases = me X Cpg (te –
tR) (kJ/min.) or (kJ/sec).
Where , mg is the mass of exhaust gases in kg/min.
te = Temperature of burnt gases coming out of the engine.
tR= room 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.

20.  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”.