ABM CABM BAU RANCHI

1. Farm Machinery And Power
Terminology Connected With Engine Power

2. Top dead center - When the piston is at the top of its stroke, it is said to be atthe
top dead center (TDC),
Bottom dead center - when the piston is at the bottom of its stroke, it is said tobe
at its bottom dead center (BDC).
Scavenging The process of removal of burnt or exhaust gases from theengine
cylinder is known as scavenging.

3. TERMINOLOGY CONNECTED WITH ENGINE POWER
Bore- Bore is the diameter of the engine cylinder.
Stroke - It is the linear distance traveled by the piston from Top dead center(TDC)
to Bottom dead center (BDC).

4. TERMINOLOGY CONNECTED WITH ENGINE POWER
Stroke-bore ratio -The ratio of length of stroke (L) and diameter of bore (D) of the
cylinder is called stroke-bore ratio (L/D).
In general, this ratio varies between 1 to 1.45 and for tractor engines, this ratio is
about 1.25.
Swept volume - It is the volume (A x L) displaced by one stroke of the piston
whereAis the cross sectional area of piston and L is the length of stroke

5. Compression ratio –
 It is the ratio of the volume of the cylinder at the beginning of the compression
stroke to that at the end of compression stroke,
 i.e. ratio of total cylinder volume to clearance volume.
 The Compression ratio of diesel engine varies from 14:1 to 22:1 and thatof
carburetor type engine (spark ignition engine) varies from 4:1 to8:1.

6. Power
 It is the rate of doing work. S.I. unit of power iswatt.
 Watt = Joule/sec. (4.2 Joules = 1 Calorie).
 In metric unit the power can be expressed in kg.m/sec
• Horse power (HP) –
o
o
o
It is the rate of doing work.
Expressed in horse power
Conversion factors from work to power
4500 kg m of work /minute = 1.0 hp
75 kg. m of work /second = 1.0 hp

7. Indicated horse power (IHP) –
 It is the power generated in the engine cylinder and received by thepiston.
 It is the power developed in a cylinder without accounting frictionallosses.
IHP = PLAN Xx
4500 2
( for 4 stroke engine )
IHP = PLAN Xx
4500 1
( for 2 stroke engine )
P = mean effective pressure,kg/cm2
L = stroke length, m
A = cross sectional area of piston,cm2
N = engine revolution per minute
x = number of cylinders

8. In SI unit, indicated horse power is given as below:
IHP = PLAN Xx
60𝑥1012 2 ( for 4 stroke engine )
IHP = PLAN Xx
60𝑥1012 1 ( for 4 stroke engine )
where P = mean effective pressure, Pa (pascal)
L = length of stroke,mm
A = area of piston,mm2
N = speed, RPM

9. Brake horse power (BHP) –
It is the power delivered by the engine at the end of thecrankshaft.
It is measured by a dynamometer.
2ΠNT
BHP =
4500
where T = Torque inkg.m
N = speed, RPM

10. Belt horse power –
Power take-off horse power (PTO HP) –
 It is the power delivered by a tractor through its PTO shaft.
 In general, the belt and PTO horse power of a tractor will approximately be the
same.
 The PTO hp is around 80-85% 0f tractor enginepower
Drawbar horse power (DBHP) –
 It is the power of a tractor measured at the drawbar of a tractor.
 It is that power which is available for pullingloads.
 It is around 50-55 % of engine power.
Frictional horse power (FHP) –
It is the power required to run the engine at a given speed without producingany
useful work.
It represents the friction and pumping losses of an engine.
IHP = BHP +FHP

11. Efficiencies of an IC Engines
Piston displacement : it is the volume displaced by one stroke of
the piston. It is also known as swept volume.
Piston displacement = A x L
Displacement volume : it is the total swept volume of all the piston
during power strokes occurs in one minute.
Displacement volume = A x L x n x (X/2) (For 4 stroke engine)
Displacement volume = A x L x n x (X/1) (For 2 stroke engine)
Piston speed : It is the total length of travel of piston in a cylinder in
one minute
Sp = 2 x L x n

12. Mechanical efficiency :
The ratio of Brake Power to indicated power is called mechanical
efficiency
Thermal efficiency :
The ratio of output in the form of useful mechanical Power to the
power value of the fuel consumed.
Thermal Efficiency =
mechanical Power
Power value of fuel
x 100
Indicated thermal Efficiency
=
Indicated Power
mf  C.V
x 100
Brake thermal Efficiency
=
Brake Power
mf  C.V
x 100
mf = mass of fuel CV= Calorific value of fuel

13. Relative efficiency
The ratio of indicated thermal efficiency to the air standard efficiency

14. Volumetric Efficiency
The ratio of actual weight of air introduced by the engine on
the suction stroke to the theoretical weight of the air that
should have been introduced by filling the piston
displacement volume with air at atmospheric pressure and
temperature.