This set of Automotive Engine Auxiliary Systems Multiple Choice Questions & Answers (MCQs) focuses on “Petrol Engine Fuel Supply System – Simple Carburettor”.
1. Which of the following material is used to make the float of a carburetor?
b) Sheet metal
c) Nylon plastic
d) Cast iron
Explanation: The floats have a tendency to leak along the joint seams.due to which they are made of nylon plastic or expanded synthetic rubber. The needle valve attached to the float serves to close or open the fuel inlet to the float chamber depending on the requirements.
2. Which of the following is provided in the float chamber to keep the pressure inside atmospheric?
b) Fuel jet
c) Small vent
d) Throttle valve
Explanation: A small vent in the float chamber keeps the pressure inside the atmospheric. In modern practice, it is preferred to vent the float chamber to the air intake of the carburetor. In modern practice, it is preferred to vent the float chamber to the air intake of the carburetor.
3. Which of the following increases with the reduction of area in a venturi?
Explanation: In the venturi the passage is is minimum. Thus due to less area, the air velocity increases and because of this increase in velocity, a decrease in pressure is caused at the nozzle which is located in venturi itself.
4. Which among the following does not affect the amount of fuel delivered?
a) Jet size
b) Float level
c) Venturi vacuum
d) Ignition timing
Explanation: The amount of fuel delivered depends upon the major factors like jet size, float level, and venturi vacuum. Whereas the ignition timing does not affect the amount of fuel that is being delivered to the engine via the carburetor.
5. What is the main function of a throttle valve?
Explanation: The purpose of a throttle valve is to control the quantity of the air-fuel mixture and it is attached to the accelerator pedal. Whereas there is no such great effect of the throttle valve in the factors like temperature, enthalpy, and entropy.
6. Which of the following component is used to maintain the liquid-tight seal during vibration?
a) Three-piece valve with rubber seat tip
d) Throttle valve
Explanation: A three-piece valve with a rubber seat tip and a spring-loaded ball In the body of the stem. Whereas the other components like the vent, nozzle and the throttle valve are the main parts of a carburetor which helps in the air-fuel mixture ratio.
7. What is the main function of a float in the float chamber?
a) Constant head of fuel
c) Temperature control
Explanation: The fuel starts to flow in and the float rises gradually till the fuel level reaches the desired value. At this time, the float needle closes the fuel inlet passage. Thus a constant head of fuel is maintained in the float.
8. In practice what is the fuel level in the float chamber that is maintained in millimeter below the nozzle?
Explanation: The fuel level in the float chamber is maintained about 5mm below the nozzle outlet. A small vent in the float chamber keeps the pressure inside atmospheric and in modern practice is preferred to vent the float chamber to the air intake of the carburetor.
9. How is the fuel supply from the float chamber at any time is metered?
a) Float chamber
b) Fuel jet
c) Throttle valve
Explanation: The fuel supply from the float chamber at any time is metered by a means of the fuel jet from where the fuel flows to the venturi through the discharge nozzle. The venturi is simply a restriction in the air passage where the passage area is minimum.
10. What is the correct stoichiometric ratio for an air-fuel mixture?
Explanation: The stoichiometric ratio of air-fuel is 14.7:1. It means that 14.6 parts of air and 1 part of gasoline or petrol (by mass) is the one which would give chemically correct combustion of petrol under ideal conditions.
11. Which among the following is not a function of the carburetor?
a) A small reserve of fuel at constant head
b) To vaporize the fuel to prepare a homogeneous mixture
c) To supply the correct amount of air-fuel mixture
d) To delay the ignition timing depending in the exhaust gas
Explanation: The functions of a carburetor is to keep a small reserve of fuel at the constant head, vaporize the fuel to prepare a homogeneous air-fuel mixture, supply correct amount of the air-fuel mixture at the correct strength and the ECU takes care of the ignition timing depending on the input from the oxygen sensor.
12. For which operation is the Lean air-fuel mixture required?
Explanation: During cruising the air-fuel mixture is lean as the emission is controlled by using this ratio. Where more air is burnt for the same value of the fuel when operating at sea level. These weaker mixtures provide a good economy when compared to the economy of the rich mixture.
13. Where is the throttle valve is attached to control the flow of air?
d) Hand brake
Explanation: The throttle is directly connected to the accelerator pedal wherein depending on the accelerator pedal the amount of air and fuel required is sent inside the combustion chamber.
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