The document defines various terminology related to engine power. It describes key terms such as bore, stroke, stroke-bore ratio, swept volume, compression ratio, horsepower, indicated power, brake horsepower, frictional horsepower, brake mean effective pressure, piston speed, displacement volume, and specific fuel consumption. These terms are important for understanding the operation and performance of internal combustion engines.

1. TERMINOLOGY CONNECTED
WITH ENGINE POWER
Dr. Ajay Singh Lodhi
Assistant Professor
College of Agriculture, Balaghat
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

2. TERMINOLOGY
1. Bore- Bore is the diameter of the engine cylinder.
2. Stroke - It is the linear distance traveled by the piston from Top dead centre (TDC) to
Bottom dead centre (BDC).

3. TERMINOLOGY
3. 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.
4. Swept volume - It is the volume
(A x L) displaced by one stroke of
the piston where A is the cross
sectional area of piston and L is the
length of stroke

4. TERMINOLOGY
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 that of carburetor type
engine (spark ignition engine) varies from 4:1 to 8:1.

5. TERMINOLOGY
6. Power - It is the rate of doing work. S.I. unit of
power is watt.
Watt = Joule/sec. (4.2 Joules = 1 Calorie).
1 kg = 9.8 Neuton = 9.8N
1 N.m = 1 Joule
1 N.m/s = 1 Joule/s = 1 Watt
1 kg/cm2 = 9.8 x 104 N/m2 = 9.8 x 104 Pa = 98 Kpa
1 Pa = 1 N/m2
In metric unit the power can be expressed in kg.m/s.
1 kg.m/s = 9.8 Joules/s = 9.8 Watt
1 J/s = 0.10198 Kg-m/s
1 Calorie = 4.186 Joules
1 Joule = 0.2389 Calories
1 kW-h = 860 k.calories
1 kW = 1000 W = 102 kg.m/s
7. Horse power (HP) - It is the rate of doing
work. Expressed in horse power (Hp).
Conversion factors from work to power
4500 kg m of work /minute = 1.0 hp
75 kg. m of work /second = 1.0 hp.

6. TERMINOLOGY
Indicated power (ip) - It is the power generated in the engine cylinder and received by the
piston.
It is the power developed in a cylinder without accounting frictional losses.
In Metric Unit
𝑰𝒏𝒅𝒊𝒄𝒂𝒕𝒆𝒅 𝑯𝒐𝒓𝒔𝒆 𝑷𝒐𝒘𝒆𝒓 (𝑰𝑯𝑷) =
𝑷𝑳𝑨𝑵
𝟒𝟓𝟎𝟎
×
𝒙
𝟐
𝒇𝒐𝒓 𝟒 𝒔𝒕𝒓𝒐𝒌𝒆 𝒆𝒏𝒈𝒊𝒏𝒆
𝑰𝒏𝒅𝒊𝒄𝒂𝒕𝒆𝒅 𝑯𝒐𝒓𝒔𝒆 𝑷𝒐𝒘𝒆𝒓 (𝑰𝑯𝑷) =
𝑷𝑳𝑨𝑵
𝟒𝟓𝟎𝟎
×
𝒙
𝟏
𝒇𝒐𝒓 𝟐 𝒔𝒕𝒓𝒐𝒌𝒆 𝒆𝒏𝒈𝒊𝒏𝒆
Where P = mean effective pressure, kg/cm2
L = stroke length, m
A = cross sectional area of piston, cm2
N = engine speed revolution per minute
x = number of cylinder

7. TERMINOLOGY
In SI Unit
Indicated Power (ip), kw=
𝑷𝑳𝑨𝑵
𝟔𝟎 ×𝟏𝟎𝟏𝟐 ×
𝒙
𝟐
𝒇𝒐𝒓 𝟒 𝒔𝒕𝒓𝒐𝒌𝒆 𝒆𝒏𝒈𝒊𝒏𝒆
Where P = mean effective pressure, Pa (Pascel); [1 Pa = 1N/m2)
L = stroke length, mm
A = cross sectional area of piston, mm2
N = engine speed revolution per minute
x = number of cylinder
Indicated Power (ip), kw=
𝑷𝑳𝑨𝑵
𝟔𝟎 ×𝟏𝟎𝟏𝟐 ×
𝒙
𝟏
𝒇𝒐𝒓 𝟐 𝒔𝒕𝒓𝒐𝒌𝒆 𝒆𝒏𝒈𝒊𝒏𝒆

8. TERMINOLOGY
Brake horse power (B.H.P): It is the horsepower delivered by the engine and is available
at the end of the crankshaft and it is measured by suitable dynamometer.
Belt horse power: It is the power of the engine, measured at the suitable belt, receiving
drive from the PTO shaft (power take off shaft).
Frictional horse power (F.H.P): It is the power required to run the engine at a given speed
with out producing any useful work. It represents the friction and pumping losses of the
engine.
F.H.P = I.H.P - B.H.P
I.H.P = B.H.P + F.H.P
Drawbar horse power (DBHP): It is the power of a tractor measured at the end of the
drawbar. It is the power required to pull the loads.

9. TERMINOLOGY
Brake mean effective pressure ( BMEP): It is the average pressure acting throughout the
entire power strokes which are necessary to produce BHP of the engine
Thermal efficiency: It is the ratio of the horse power output of the engine to the fuel horse power.
Mechanical efficiency: It is the ratio of the brake horse power to the indicated horse power.
Piston speed (Np) : It is the total length of travel of the piston in a cylinder in one minute. Piston
speeds of the high speed tractor engine range between 300 to 500 m/m.
BMEP =
𝐵𝐻𝑃 ×75 ×60
𝐿 ×𝐴×𝑁×
𝑛
2
(𝐹𝑜𝑟 4 𝑆𝑡𝑟𝑜𝑘𝑒 𝐸𝑛𝑔𝑖𝑛𝑒)
BMEP =
𝐵𝐻𝑃 ×75 ×60
𝐿 ×𝐴×𝑁×𝑛
(𝐹𝑜𝑟 2 𝑆𝑡𝑟𝑜𝑘𝑒 𝐸𝑛𝑔𝑖𝑛𝑒)
Mechanical Efficiency =
𝐵𝐻𝑃
𝐼𝐻𝑃
𝑋 100

10. TERMINOLOGY
Displacement volume (Vd) : It is the total swept volume of all the pistons during power
strokes occurring in a period of one minute.
𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑉𝑜𝑙𝑢𝑚𝑒 = 𝐴 × 𝐿 × 𝑛 ×
𝑥
2
(For 4 stroke engine)
𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑉𝑜𝑙𝑢𝑚𝑒 = 𝐴 × 𝐿 × 𝑛 ×
𝑥
1
(For 2 stroke engine)
Where,
A = cross sectional area of the piston
L = stroke length
n = Speed, rev/m
x = number of cylinders
 Specific Fuel Consumption: It is the quantity of fuel consumed kW-hr in an engine.

13. Thank You