1020-Diploma in Mechanical Engineering - 4020340- III Semester - Thermal Engineering I -Unit 4 : Performance of IC Engines PPT Prepared By… U. ARAVIND, B.E., M.I.S.T.E., LECTURER / MECHANICAL ENGINEERING LAKSHMI AMMAL POLYTECHNIC COLLEGE K.R. NAGAR, KOVILPATTI - 628 503 THOOTHUKUDI DISTRICT, TAMIL NADU Mobile No: 9943244068 Email Id: aravindulaganathanmech@gmail.com aravindmech@lapc.in

1. 6 April 2022 1
Lakshmi Ammal Polytechnic College
Department of Mechanical Engineering
THERMAL ENGINEERING - 1
Prepared By…
U.Aravind
Lect/Mech
LAPC
Kovilpatti

2. 6 April 2022 2
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
An internal combustion engine should be
tested to check the performance of under
various operating conditions.
• Commercial Test
• Thermodynamic Test

3. Commercial
Test
Overload
Carrying
Capacity
Lubricating
Oil
Consumption
Amount of
Cooling water
required
Valve Timings
Stability 3
6 April 2022
Prepared By.. U.Aravind, Lecturer/Mechanical, LAPC,
Kovilpatti

4. Thermodynamic Test
Compare the Actual performance of the engine
with the theoretical performance
Indicated
Mean
Effective
Pressure
Indicated
Power
Brake
Power
Fuel
Consum
ption
Heat
Carried
away by
cooling
water
Heat
Carried
away by
exhaust
gas
4
6 April 2022
Prepared By.. U.Aravind, Lecturer/Mechanical, LAPC,
Kovilpatti

5. 6 April 2022 5
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is an Algebraic sum of the mean
pressure acting on the piston during each
stroke in one complete working cycle.
•It is measured from Actual Indicated
Diagram
•Indicated Mean Effective Pressure,
pmi= h x S =
𝐀
𝐋
𝐗 𝐒

6. 6 April 2022 6
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the Actual Power developed inside an
engine Cylinder.
• It is measured with the help of Indicated
mean effective pressure.
Indicated Power, IP = pmi LAnK
• L – Stroke Length
• A – Piston Area
• n – Number of power stroke (n=N for two stroke
engine, n = N/2 for four stroke engine)
• K – No of Cylinders

7. 6 April 2022 7
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is similar to indicated mean effective
pressure but related to the Brake power
• Brake Mean Effective Pressure,
pmb = ηm x pmi

8. 6 April 2022 8
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the useful power available at the
engine Crank Shaft
• It is Less than Indicated Power
Brake Power, BP = 2πNT
Brake Power, IP = pmb LAnK
• T, Torque = W x R

9. 6 April 2022 9
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
Brake Power Measurement:
• Prony Brake Dynamometer
• Rope Dynamometer
• Electrical Dynamometer
• Hydraulic Dynamometer

10. 6 April 2022 10
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the power lost due to the friction of
moving parts.
• It is difference between indicated power
and brake power.
Friction Power, FP = IP - BP

11. Efficiency of
Engines
Mechanical
Efficiency
Indicated
Thermal
Efficiency
Brake
Thermal
Efficiency
Relative
Efficiency
Volumetric
Efficiency 11
6 April 2022
Prepared By.. U.Aravind, Lecturer/Mechanical, LAPC,
Kovilpatti

12. 6 April 2022 12
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the Ratio of Brake Power to Indicated
Power.
Mechanical Efficiency,
ηm =
Brake Power
Indicated Power
=
BP
IP
ηm =
Brake Thermal Efficiency
IndicatedThermal Efficiency
=
ηBT
ηIT
ηm =
Brake mean Effective Pressure
Indicatedmean Effective Pressure
=
pm𝒃
pmi

13. 6 April 2022 13
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the Ratio of Indicated Power to Heat
Supplied
•It is also called Actual Thermal Efficiency
or Thermal Efficiency
Indicated Thermal Efficiency,
ηI.T =
Indicated Power
Heat Supplied
=
𝐈𝐏
𝐅𝐂
𝟑𝟔𝟎𝟎
𝐱 𝐂𝐕
𝐱 𝟏𝟎𝟎

14. 6 April 2022 14
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the Ratio of Brake Power to Heat
Supplied
•It is also called Overall Efficiency (25% -
30%)
Brake Thermal Efficiency,
ηB.T =
Brake Power
Heat Supplied
=
𝐁𝐏
𝐅𝐂
𝟑𝟔𝟎𝟎
𝐱 𝐂𝐕
𝐱 𝟏𝟎𝟎

15. 6 April 2022 15
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the Ratio of Indicated Thermal
Efficiency to the Theoretical(Ideal)
Thermal Efficiency
•It is also called Efficiency Ratio (60% -
80%)
Relative Efficiency,
ηrel =
Indicated Thermal Efficiency
Ideal Thermal Efficiency
=
η𝐁𝐓
η𝐈𝐝𝐞𝐚𝐥

16. 6 April 2022 16
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is defined as the ratio of the actual
volume of charge admitted into the engine
cylinder during suction to the stroke
volume
Volumetric Efficiency,
ηvol =
Volume of the charge admitted during
suction
Stroke Volume
=
V𝐧
V𝐬

17. 6 April 2022 17
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti
• It is the amount of fuel consumption to
obtain one brake power – hour of work.
•It is also called Brake Specific Fuel
Consumption (BSFC)
BSFC =
FC
BP

18. 6 April 2022 18
U.Aravind, Lecturer/Mechanical, LAPC, Kovilpatti