250+ TOP MCQs on Petrol Engine Fuel System and Answers

Automobile Engineering Multiple Choice Questions on “Petrol Engine Fuel System”.

1. When is the choke used in the engine?
a) When the vehicle is idling
b) When the vehicle is accelerating
c) When the engine is cold
d) When the engine is hot
Answer: c
Clarification: The choke is used when the engine is cold. The choke is a butterfly valve located between the entrance to the carburetor and the venturi throat.

2. What does the venturi in carburetor cause?
a) Increase of air velocity
b) A decrease in air velocity
c) A decrease in fuel flow
d) Decrease of manifold vacuum
Answer: a
Clarification: The venturi in carburetor causes an increase in air velocity. The main function of the carburetor are to keep a reserve of fuel at a constant head.

3. Where is the lean air-fuel mixture needed?
a) During starting
b) During idling
c) During acceleration
d) During cruising
Answer: d
Clarification: The lean air-fuel mixture is needed during cruising. In this range, it is desirable that the carburetor provides the engine with the best fuel economy.

4. Which of the following is the most widely used fuel supply system?
a) Gravity system
b) Pressure system
c) Pump system
d) Vacuum system
Answer: c
Clarification: The most widely used fuel supply system is the pump system. In this system, a steel pipe carries petrol to the fuel pump which pumps into the float chamber through a flexible pipe.

5. Why is the small hole provided in the pump body?
a) A vent for the oil
b) A vent for water
c) A vent for air
d) A vent for the fuel
Answer: c
Clarification: The small hole is provided as a vent for air in the pump body. This is an escape for excess air in the pump. So that pump does not get overloaded.

6. Which of the following is the most accurate petrol injection system?
a) Manifold injection
b) Port injection
c) Throttle body injection
d) Direct injection
Answer: b
Clarification: The most accurate petrol injection system is port injection. In this system, the injector sprays the fuel into each intake port on the manifold side of the inlet valve.

7. Where does the power for mechanical fuel pump come from?
a) Camshaft
b) Crankshaft
c) Distributor shaft
d) Propeller shaft
Answer: a
Clarification: The power for mechanical fuel pump comes from the camshaft by means of an eccentric cam.

8. If petrol has a density of 800 kg/m³ and the discharge nozzle is located 8 mm above the level of petrol in a float chamber. What is the pressure differential causing airflow?
a) 62.78 Pa
b) 42.78 Pa
c) 52.78 Pa
d) 72.78 Pa
Answer: a
Clarification: When the fuel flow just starts ΔP_f = 0 i.e. ΔP_a – ghρ_f = 0. (ΔP_f = pressure differential causing fuel flow, ΔP_a = pressure differential causing airflow, h = height of nozzle above the fuel level, ρ_f = density of fuel) ΔP_a – 9.81*(8*10^-3)*800 = 0 i.e. ΔP_a = 62.78 Pa.

9. What is the pressure differential causing fuel flow if the venturi depression is found to be 105 cm of water?
a) 10300.5 Pa
b) 20300.5 Pa
c) 50300.5 Pa
d) 60300.5 Pa
Answer: a
Clarification: Pressure differential causing fuel flow = ΔP_f, ρ = density of water, h = height of nozzle above the fuel level. ΔP_f = g*h*ρ = 9.81*1.05*1000 = 10300.5 kg/m².

10. What is the value of the rate of flow of fuel if the coefficient discharge of fuel is 0.75, area of the jet is 0.885 mm², density of the fuel is 780 kg/m³, and pressure differential causing fuel flow is 15000 Pa?
a) 3.21 g/s
b) 4.21 g/s
c) 5.21 g/s
d) 6.21 g/s
Answer: a
Clarification: Pressure differential causing fuel flow = ΔP = 15000 Pa, coefficient of discharge = C_f = 0.75, density of the fuel = ρ = 780 kg/m³, and area of the jet = A = 0.885 mm². The rate of flow of fuel = W_f = A* C_f*(sqrt{2rhoDelta P}) = 0.885*0.75*10^-6*(sqrt{2*780*15000}) = 3.21*10^-3 kg/s = 3.21g/s.