How Does Carburettor works

How Does Carburettor works?

Introduction

The combustion of the fuel with oxygen in the combustion chamber provides the energy necessary to drive the piston. In the S.I engine the liquid are generally mixed prior to their arrival in the combustion chamber. The process of preparing this mixture is called as carburetion.

In the engine, the desired air-fuel ratio means that gives the maximum economy. Actual air-fuel mixture requirements in an operating engine vary under variable load and speed condition. The air-fuel ratio must be changed based on whether the maximum economy or maximum power is required.

A carburettor is a device which is used in the vehicle to prepare a homogeneous mixture of air and fuel for the working of the engine.

The main function of a carburettor are.....

       1. Combine gasoline and air and produce a high combustible mixture.

       2. Regulate the air-fuel ratio

       3. maintain the engine speed.

working

Liquid fuel is supplied to the carburettor from the fuel tank system which consists of the fuel supply tank, fuel pump, lines and filter. Air is drawn into the carburettor from the atmosphere during suction in the engine cylinders. Most of the air engine induct the air directly into the carburettor through an air cleaner. The carburettor supplies air-fuel mixture to the engine cylinders through intake manifold and quantity of mixture entering the cylinder is regulated by the throttle.

Choke
It usually happens, when the vehicle doesn't get started, and word choke is used but what is it actually, 
To start the cold engine, a rich mixture is needed. To provide the rich mixture, choke valve is fitted in the air intake passage of the carburettor. The choke valve is in the form of a circular disc like the throttle valve. This choke is operated to shut off partially the supply of air to the carburettor. During the suction stroke, less amount of air and the more amount of fuel is sucked and a rich mixture is obtained. Immediately after starting the cold engine the choke valve should be open for full air supply.

Venturi

A venturi is a narrow space in the cylindrical air horn, through which the air passes. As the same amount of air must pass through every point in the air horn, its velocity will be greatest at the narrow point. The more the area is reduced, the greater will be the velocity of air.

The spray of gasoline from the nozzle an air entering through the venturi are mixed together in the mixing chamber which is just below the discharge jet. The mixture passes through the intake manifold into the cylinder.

Throttle valve

It is a circular disc located in the mixing chamber of the air horn. It can be tilted to open or close the air horn to allow more or less air to flow through it. When it is tilted to open, more air passes the venturi sucking more fuel, thus more amount of air-fuel mixture goes to the cylinder. The engine develops more power and tends to run faster. When the throttle valve is tilted to close, less air passes the venturi sucking less fuel, thus less amount of air-fuel mixture goes to the cylinders. The engine develops less power and tends to run slowly.

Metering system

As the engine speed increases beyond the certain limit, suction also increases. The flow of the fuel from the jet increases faster than the corresponding flow of air. Thus mixture becomes richer. To maintain the correct air-fuel mixture at high speed.

Advantages

• Improves atomization
• Better fuel distribution
• Smooth idle
• Improves power and reduce emissions
• It allows use of inferior fuels.
• Maintenances cost is less and easy repair.
• Simple and Overall cost is less.

Disadvantages

• More air emissions than the fuel injector
• To start the cold engine is difficult.
• Complete combustion of is a challenge.
• Spark plug fouling issue is very common.