1. I.C. ENGINES
LECTURE NO: 13
(28 Apr 2014)

2. ENGINE PERFORMANCE PARAMETERS
Indicated Thermal Efficiency
Brake Thermal Efficiency
Mechanical Efficiency
Volumetric Efficiency
Relative Efficiency
Mean Effective Pressure
Mean Piston Speed
Specific Power Output
Specific Fuel Consumption

3. ENGINE PERFORMANCE PARAMETERS
Inlet Value Mach Index
Fuel Air Ratio
Calorific Value of the Fuel

4. Atmospheric Pressure

5. Work
Work is the movement of a body against an opposing force.

6. Torque

7. Conversion of Work into Torque

8. Power Rate of doing Work is called power
Through testing, it was found that the average horse could lift a 200-lb. weight to a height of 165 ft in 1 minute. The equivalent of one horsepower can be reached by multiplying 165 ft by 200 lb. (work formula) for a total of 33,000 ft lb. per minute

9. Power

10. Dynamometer
Pony Brake

11. Dynamometer

12. Classic Dynamometer

13. Indicated Thermal Efficiency
Indicated thermal efficiency is the ratio of energy in the indicated power ip, to the input fuel energy in appropriate units
ηith = ip [kJ/s]
energy in fuel per second [kJ/s]
ηith = ip [kJ/s]
mass of fuel/s x calorfic value of fuel

14. Brake Thermal Efficiency
Brake thermal efficiency is the ratio of energy in the brake power bp, to the input fuel energy in appropriate units
ηbth = bp [kJ/s]
energy in fuel per second [kJ/s]
ηith = ip [kJ/s]
mass of fuel/s x calorific value of fuel

15. Mechanical Efficiency
Mechanical efficiency is the ratio of bp (delivered power) to indicated power ( power provided to the piston)
ηm = bp [kJ/s] = bp
ip [kJ/s] bp+fp
fp = ip - bp

16. Volumetric Efficiency
Volumetric efficiency is the ratio actual volume flow rate of air into the intake system to the rate at which the volume is displaced by the system .
ηv = ma / ρa
V disp N/2
ρa = Inlet density
SI = 80 to 85 %
CI = 85 to 90 %

17. Volumetric Efficiency
Alternative equivalent definition of Volumetric
𝜂 𝑣 = 𝑚 𝑎 ρ 𝑎 𝑉 𝑎
ρ 𝑎 = is atmospheric air density
𝜂 𝑣 = the pumping performance of the entire inlet system
And if it is taken as the air density in the manifold then 𝜂 𝑣 is the pumping performance of the inlet port and valve only

18. Relative Efficiency or Efficiency Ratio
Relative efficiency is the ratio thermal efficiency of actual cycle to ideal cycle .
ηrel = Actual Thermal Efficiency
Air Standard Efficiency

19. Mean Effective Pressure
𝑖 𝑝 = 𝑝 𝑖𝑚 𝐿𝐴 𝑛𝐾 60 ×1000
ip = Indicated power [kW]
pim = Indicated mean effective pressure [N/m2 ]
L = Length of the stock [m]
A = Area of the piston [m2]
N = Speed in revolutions per minute [rpm]
n = Number of stock N/2 & N
K = Number of cylinder
𝑝 𝑖𝑚 = 𝑖 𝑝 6000 𝐿𝐴𝑛𝐾

20. Mean Effective Pressure
indicated mean effective pressure is
𝑝 𝑖𝑚 = 𝑖 𝑝 6000 𝐿𝐴𝑛𝐾
Break mean effective pressure is
𝑝 𝑏𝑚 = 𝑏 𝑝 6000 𝐿𝐴𝑛𝐾
ip = Indicated power [kW]
pim = Indicated mean effective pressure [N/m2 ]
L = Length of the stock [m]
A = Area of the piston [m2]
N = Speed in revolutions per minute [rpm]
n = Number of stock N/2 & N
K = Number of cylinder

21. Mean Piston Speed Sp = 2LN L = Length of the stock [m]
N = Crank Speed in revolutions per minute [rpm]

22. Specific Power Output
Ps = bp/A
= constant x pbm x Sp

23. Specific Fuel Consumption
sfc = Fuel Consumption per unit Time
Power

24. Inlet – Valve Mach Index (Z)
𝑢= 𝐴 𝑝 𝐶 𝑖 𝐴 𝑖 𝑉 𝑝
u = Gas velocity through the inlet valve
Ap = piston area
Ai = nominal intake valve operating area
Ci = inlet valve flow coefficient

25. Inlet – Valve Mach Index (Z)
𝑢 𝛼 = 𝐴 𝑝 𝐴 𝑖 𝑉 𝑝 𝐶 𝑖 =( 𝑏 𝐷 𝑖 ) 2 𝑉 𝑝 𝐶 𝑖 =𝑍
Where
b = cylinder diameter
Di = inlet valve diameter
V = mean piston speed
𝛼 = inlet sonic velocity
C = inlet valve average flow coefficient
Z = inlet valve Mach index

26. Fuel – Air ( F/A) or Air –Fuel Ratio (A/F)
ϕ= 𝐴𝑐𝑡𝑢𝑎𝑙 𝑓𝑢𝑒𝑙−𝑎𝑖𝑟 𝑟𝑎𝑡𝑖𝑜 𝑆𝑡𝑜𝑖𝑐ℎ𝑖𝑜𝑚𝑒𝑡𝑟𝑖𝑐 𝑓𝑢𝑒𝑙−𝑎𝑖𝑟 𝑟𝑎𝑡𝑖𝑜
Where
ϕ = 1 means stoichiometric ( chemically correct) mixture
ϕ ˂ 1 means lean mixture
ϕ ˃ 1 means rich mixture

27. Calorific Value ( CV)
Calorific value of a is the thermal energy released per unit quantity of the fuel when the fuel is burning completely and the products of combustion are cooled back to the initial temperature of the combustible mixture.

28. PROBLEMS

29. PROBLEM NO 1
The Mechanical effencicy of a single cylinder four stroke engine is 80 %. The frictional power is esitmated to be 25 kW. Calculate:- Ip bp

30. SOLUTION
ηm = bp/ip
fp = ip - bp

31. PROBLEM NO 2
A 42.5 kW has a mechanical efficiency of 85%. Find the ip and fp. If the frictional power is assumed to be constant with load, What will be mechanical efficiency at 60 % of the load?

32. SOLUTION
ηm = bp / ip
fp = ip – bp
ηm = bp / (bp + fp)