PPT describes the engine performance parameters of the I.C. engine. Engine performance is an indication of the degree of success of the engine performs its assigned task, i.e. the conversion of the chemical energy contained in the fuel into the useful mechanical work. The engine performance is indicated by the term efficiency, η. Five important engine efficiencies and other related engine performance parameters are: Power Indicated Thermal Efficiency (ηith) Brake Thermal Efficiency (ηbth) Mechanical Efficiency (ηm) Volumetric Efficiency (ηv) Relative Efficiency or Efficiency Ratio (ηrel) Mean Effective Pressure (Pm) Specific Fuel Consumption (sfc) Fuel-Air or Air-Fuel Ratio (F/A or A/F) Calorific Value (CV) Power:- The main purpose of running an engine is to obtain mechanical power. Brake Power (B.P.) The power developed by an Engine at the output shaft is called the brake power. Brake Power= Brake Workdone/Time B.P.=BWD/sec. Indicated power (I.P.) The total power developed by Combustion of fuel in the combustion chamber is called indicated power. Indicated Power= Indicated Workdone/Time I.P.=IWD/sec. Frictional Power (F.P.) The difference between I.P. and B.P. is called frictional power (f.p.). FP = IP – BP Thermal Efficiency (ηth) Thermal efficiency is the ratio of Power to energy supplied by the fuel. ηth= Power/ Energy In I.C. Engine, thermal efficiency can be classified into two categories i.e. Indicated Thermal Efficiency (ηith) Indicated thermal efficiency is the ratio of indicated power to the heat supplied or added. ηith= IP/Qs 2. Brake Thermal Efficiency (ηith) Brake Thermal Efficiency is the ratio of brake power to the heat supplied or added. ηbth= BP/Qs Volumetric Efficiency (ηv) This is one of the most important parameters which decide the performance of four-stroke engines. Four stoke engines have distinct suction stoke, volumetric efficiency indicates the breathing ability of the engine. Volumetric efficiency is defined as the ratio of actual flow rate of air into the intake system to rate at which the volume is displaced by the system. ηv= (푚 ̇"a/a" )/(푉푑푖푠푝푎푐푒푑 푋 푁/2) "a"= Inlet density is taken atmospheric air density N= Number of the cylinder in use

1. ENGINE PERFORMANCE
PARAMETERS
By Lokendra Kumar
Assistant Professor
Department of Mechanical Engineering
JIET, Jodhpur (Rajasthan), 342802

2. INTRODUCTION
Engine performance is an indication of the degree of
success of the engine performs its assigned task, i.e. the
conversion of the chemical energy contained in the fuel
into the useful mechanical work. The engine performance
is indicated by the term efficiency, η. Five important engine
efficiencies and other related engine performance
parameters are:
a) Power
b) Indicated Thermal Efficiency ( η ith)
c) Brake Thermal Efficiency (η bth)
d) Mechanical Efficiency (η m)
e) Volumetric Efficiency (η v)
f) Relative Efficiency or Efficiency Ratio (η rel)
g) Mean Effective Pressure (Pm)
h) Specific Fuel Consumption (sfc)
i) Fuel-Air or Air-Fuel Ratio (F/A or A/F)
j) Calorific Value (CV)

3. Power:-
The main purpose of running an engine is to obtain mechanical
power.
Power is defined as the rate of doing work and is equal to the
product of force and linear velocity or the product of torque and
angular velocity.
Power (P)= Torque (T) x Angular velocity (ω)
P=T ω
Or
Power can also be written in the form of workdone per unit time i.e.
Power= Workdone/Time
In I.C. Engine, power is classified into three categories i.e.
1. Brake Power or Brake Horse Power (bhp or bp)
2. Indicated power or indicated horse power (ihp or ip)
3. Frictional Power (F.P.)

4. Brake Power (B.P.)
The power developed by an Engine at the output shaft is called the brake
power.
Brake Power= Brake Workdone/Time
B.P.=BWD/sec.
Indicated power (I.P.)
The total power developed by Combustion of fuel in the combustion
chamber is called indicated power.
Indicated Power= Indicated Workdone/Time
I.P.=IWD/sec.
Frictional Power (F.P.)
The difference between I.P. and B.P. is called frictional power (f.p.).
FP = IP – BP
Mechanical Efficiency (ηm) – It is the ratio of brake power to the
indicated power i.e.
ηm =BP/IP

5. Thermal Efficiency (ηth)
Thermal efficiency is the ratio of Power to energy supplied by the
fuel.
ηth= Power/ Energy
In I.C. Engine, thermal efficiency can be classified into two
categories i.e.
1. Indicated Thermal Efficiency (ηith)
Indicated thermal efficiency is the ratio of indicated power to the
heat supplied or added.
ηith= IP/Qs
2. Brake Thermal Efficiency (ηith)
Brake Thermal Efficiency is the ratio of brake power to the heat
supplied or added.
ηbth= BP/Qs

6. Volumetric Efficiency (ηv)
This is one of the most important parameters which decide
the performance of four-stroke engines. Four stoke engines
have distinct suction stoke, volumetric efficiency indicates
the breathing ability of the engine.
Volumetric efficiency is defined as the ratio of actual flow
rate of air into the intake system to rate at which the
volume is displaced by the system.
ηv=
𝑚a/ a
𝑉𝑑𝑖𝑠𝑝𝑎𝑐𝑒𝑑 𝑋 𝑁/2
a= Inlet density is taken atmospheric air density
N= Number of cylinder in use

7. Relative Efficiency or Efficiency Ratio(ηrel)
Relative efficiency is the ratio of thermal efficiency of an actual cycle to that of
the ideal cycle. The efficiency ratio is a very useful criterion which indicates the
degree of development of the engine.
ηrel =
𝑨𝒄𝒕𝒖𝒂𝒍 𝒕𝒉𝒆𝒓𝒎𝒂𝒍 𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚
𝑨𝒊𝒓−𝑺𝒕𝒂𝒏𝒅𝒂𝒓𝒅 𝑬𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚
Mean Effective Pressure (Pmean)
Mean effective pressure is the average pressure inside the cylinders
of an internal combustion engine based on the calculated or
measured power output. It can be expressed as the ratio of
Workdone to the Swept volume.
Pmean= Workdone/Swept volume
Pmean= WD/V2-V1

8. Specific Fuel Consumption (sfc)
The Fuel Consumption characteristics of an engine are generally
expressed in terms of specific fuel consumption in kilograms of
fuel per kilowatt-hour.
It is an important parameter that reflects how good the engine
performance is.
It is inversely proportional to the thermal efficiency of the engine
Sfc=
𝐹𝑢𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒
𝑃𝑜𝑤𝑒𝑟
Brake Specific fuel consumption (bsfc)
bsfc=
𝐹𝑢𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒
𝐵𝑟𝑎𝑘𝑒 𝑃𝑜𝑤𝑒𝑟
Indicated Specific fuel consumption (isfc)
isfc=
𝐹𝑢𝑒𝑙 𝑐𝑜𝑛𝑠𝑢𝑚𝑝𝑡𝑖𝑜𝑛 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒
𝐼𝑛𝑑𝑖𝑐𝑎𝑡𝑒𝑑𝑃𝑜𝑤𝑒𝑟

9. Calorific Value (CV)
Calorific value of a fuel is the thermal energy released per unit
quantity of the fuel when the fuel is burned completely and the
products of combustion are cooled back to the initial temperature
of the combustible mixture.
Heat added per kg of fuel = Calorific Value (CV)
HA/sec = C.V. x mf/sec
HA/sec= (HA/kg of fuel) x mf/sec