Which of the following best describes the primary function of a simple carburetor in a petrol engine?

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RRB JE CBT 2 (Mechanical Engineering) ReExam Official Paper (Held On: 04 Jun, 2025)

Answer 1

Explanation:

Simple Carburetor:

A simple carburetor is a critical component in petrol (spark-ignition) engines. Its primary function is to atomize and mix fuel with air in the proper ratio required for efficient combustion. The carburetor ensures that the engine receives the correct air-fuel mixture for various operating conditions, such as idling, acceleration, cruising, and deceleration.
In a petrol engine, the combustion process requires a specific air-fuel ratio for optimal performance. The ideal ratio, known as the stoichiometric ratio, is approximately 14.7:1, meaning 14.7 parts of air to 1 part of fuel by weight. However, depending on the operating conditions, the engine may require a richer (more fuel) or leaner (less fuel) mixture. The carburetor is designed to adjust the air-fuel mixture dynamically to meet these requirements.

Working of a Simple Carburetor:

Air Flow: Air enters the carburetor through the air intake. The airflow is controlled by a throttle valve, which adjusts the engine's power output by changing the volume of air entering the engine.
Fuel Atomization: Fuel is drawn from the fuel reservoir into the carburetor's venturi, a narrow passage where the air velocity increases, creating a low-pressure zone. This pressure difference causes the fuel to atomize, breaking it into tiny droplets.
Air-Fuel Mixing: The atomized fuel mixes with the incoming air to form a homogenous air-fuel mixture. The mixture's composition is regulated using jets and needles within the carburetor.
Delivery to Combustion Chamber: The air-fuel mixture is then delivered to the engine's combustion chamber, where it is ignited by the spark plug to produce power.