Questions set 70

Supercharging of IC Engines

1.      What is the purpose of the supercharger?
a) To increase the pressure
b) To increase the speed of the engine
c) To increase the gear ratio
d) To increase the cooling rate
Answer: a
Explanation: The purpose of the supercharger is to increase the pressure of the charge. Brake power = brakemeaneffectivepressureXsweptvolumeXno.ofcylinderXno.ofpowerstrokes60000 . From the formula, by increasing the brake mean effective pressure brake power can be increased.

2.      Which of the following is not the effect of supercharging?
a) Improved cold starting
b) Increased gas loading
c) Reduced exhaust smoke
d) Increased thermal loads
Answer: d
Explanation: The supercharging used for an improved cold start, increased gas loading, reduced exhaust smoke, increased mechanical efficiency, etc. The disadvantage of the supercharger is that it uses the crankshaft of the engine to drive.

3.      When the supercharger draws power from engine exhaust gases with the help of gas turbine, what is the supercharger called?
a) Turbocharger
b) Vane type supercharger
c) Root’s supercharger
d) Centrifugal type supercharger
Answer: a
Explanation: The supercharger which uses the engine exhaust gases for increasing the brake power is called the turbocharger. The frictional and thermal losses are less.

4.      Which type of supercharger is used at low speeds?
a) Centrifugal type supercharger
b) Vane type supercharger
c) Root’s supercharger
d) Twin-screw supercharger
Answer: a
Explanation: Centrifugal type supercharger is used at low speeds. The belt from the engine drives the supercharger. The mixture coming out of the supercharger is at high pressure.

5.      Which of the following is the advantage of Root’s supercharger?
a) It occupies less space
b) It consumes less power
c) It has minimum maintenance
d) It produces high pressure
Answer: c
Explanation: One of the advantages of Root’s supercharger is that it has minimal maintenance. Root’s supercharger works similar to the gear pump. It consists of two rotors which are connected to each other by means of gear.

6.      How does the supercharger increase power output?
a) By increasing the charge pressure
b) By increasing the charge temperature
c) By increasing the speed of the engine
d) By increasing the quantity of fuel admitted
Answer: a
Explanation: The supercharger increases the power output of the engine by increasing the charge pressure. The brake of the engine depends on the brake mean effective pressure.

7.      What is used to run the supercharging air compressor?
a) Separate electric motor
b) Engine
c) Exhaust gas turbine
d) Gear pump
Answer: b
Explanation: Engine is used to run mechanically driven supercharger. The engine crankshaft is coupled with the air compressor of the supercharger which drives the air compressor in the supercharger.

8.      Why is there a need for charge cooling?
a) To increase the engine operating temperature
b) To reduce the engine operating temperature
c) To decrease the density of air
d) To increase the exhaust temperature
Answer: a
Explanation: When the air in the supercharger gets compressed, it gets hot. Its temperature gets increased more than the ambient air temperature.

9.      What is the brake power if the swept volume is 3.5 liters, brake mean effective pressure is 10 bars, and speed is 6000 rpm?
a) 175 kW
b) 17.5 kW
c) 1.75 kW
d) 1750 kW
Answer: a
Explanation: Given swept volume = 3.5 liters, brake mean effective pressure = 10 bars & speed = 6000 rpm.
Brake power = brakemeaneffectivepressureXsweptvolumeXno.ofcylinderXno.ofpowerstrokes60000
= 3.5×10×105×60001000×60000×2 = 175 kW.

10.  The turbocharger makes use of the power from the engine so that it increases the pressure.
a) True
b) False
Answer: b
Explanation: The turbocharger makes use of the exhaust gases from the engine to drive the gas turbine. In this type of supercharger, there is no linkage between the turbocharger and the engine.