Engine Power Questions and Answers

This set of IC Engines Multiple Choice Questions & Answers (MCQs) focuses on “Engine Power”.

1. The total power developed by combustion of fuel in the combustion chamber is called ____________
a) brake power
b) indicated power
c) mean effective pressure
d) none of the mentioned
View Answer

Answer: b
Explanation: Indicated power is defined as the total power developed by combustion of fuel in the combustion chamber while brake power is defined as the power developed by an engine at the output shaft and mean effective pressure is defined as the hypothetical pressure which is thought to be acting on the piston throughout the power stroke.

2. The power developed by an engine at the output shaft is called ____________
a) brake power
b) indicated power
c) mean effective pressure
d) none of the mentioned
View Answer

Answer: a
Explanation: Brake power is defined as the power developed by an engine at the output shaft while indicated power is defined as the total power developed by combustion of fuel in the combustion chamber and mean effective pressure is defined as the hypothetical pressure which is thought to be acting on the piston throughout the power stroke.

3. The hypothetical pressure which is thought to be acting on the piston throughout the power stroke is called ____________
a) brake power
b) indicated power
c) mean effective pressure
d) none of the mentioned
View Answer

Answer: c
Explanation: Mean effective pressure is defined as the hypothetical pressure which is thought to be acting on the piston throughout the power stroke and brake power is defined as the power developed by an engine at the output shaft while indicated power is defined as the total power developed by combustion of fuel in the combustion chamber.

4. A 4-cylinder four stroke petrol engine develops 14.7 KW at 1000 r.p.m. The mean effective pressure is 5.5 bar. Calculate the bore and stroke of the engine, if the length of stroke is 1.5 times the bore.
a) 87.9 mm and 131.8 mm
b) 90 mm and 134 mm
c) 97.4 mm and 138 mm
d) none of the mentioned
View Answer

Answer: a
Explanation: Number of cylinder, n = 4
Power developed, P = 14.7 kW
Engine speed, N = 1000 r.p.m.
Indicated mean effective pressure, P_mi = 5.5 bar
Length of stroke, L = 1.5D (bore)
For four stroke cycle, k = 1/2
Indicated power developed, I.P. = (nP_miLANk x 10)/6 kw
14.7 = (4 x 5.5 x 1.5D x (pi/4 x D²)x 1000 x 1/2 x 10)/6
therefore, D³ = 0.0006806
or, D = 0.0879 or 87.9 mm
and L = 1.5 x 87.9 = 131.8 mm.

5. A single cylinder, four stroke cycle oil engine is fitted with a rope brake. The diameter of the brake wheel is 600 mm and the rope diameter is 26 mm. The dead load on the brake is 200 N and the spring balance reads 30 N. If the engine runs at 450 r.p.m., what will be the brake power of the engine?
a) 2 kW
b) 2.5 kW
c) 3 kW
d) 3.5 kW
View Answer

Answer: b
Explanation: Diameter of the brake wheel, D_b = 600 mm = 0.6 m
Rope diameter, d = 26 mm = 0.026 m
Dead load on the brake, W = 200 N
Spring balance reading, S = 30 N
Engine speed, N = 450 r.p.m.
Brake Power, B.P. = ((W – S)pi(D_b + d)N)/60 x 1000
= ((200 – 30)pi(0.6 + 0.026) x 450)/60 x 1000
= 2.5 kW.

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6. The brake output per unit of piston displacement is defined as brake power.
a) True
b) False
View Answer

Answer: b
Explanation: The brake output per unit of piston displacement is defined as specific output.

7. What are the types of absorption dynamo meters?
a) prony brake
b) rope brake
c) hydraulic brake
d) all of the mentioned
View Answer

Answer: d
Explanation: Common forms of absorption dynamo meters are :
i) prony brake
ii) rope brake
iii) hydraulic brake
iv) fan brake
v) electrical brake dynamo meters.

8. Transmission dynamo meters are also known as ____________
a) rope brake
b) hydraulic brake
c) torque meters
d) none of the mentioned
View Answer

Answer: c
Explanation: Transmission dynamo meters are also known as torque meters while rope brake and hydraulic brake are types of absorption dynamo meters.

9. The brake power is the power available ____________
a) in the engine cylinder
b) at the crank shaft
c) at the crank pin
d) none of the mentioned
View Answer

Answer: b
Explanation: The power developed by an engine at the output shaft and is only available at the crank shaft.

10. The frictional power (F.P) is given by ____________
a) F.P. = B.P.-I.P.
b) F.P. = I.P.-B.P.
c) F.P. = B.P./I.P.
d) F.P. = I.P./B.P.
View Answer

Answer: b
Explanation: The frictional power is the difference between indicated power and brake power. So Mathematically,
F.P = I.P.-B.P.

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