Page 110 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

x Pressure and vacuum: In the compression stroke of the engine, both the valves (inlet and outlet) are closed
due to which the fuel in the combustion chamber is compressed, that is, the pressure of the fuel in the
combustion chamber is increased. As a result, fuel is atomized and complete combustion of fuel occurs
successfully. Under suction stroke in the engine, only the inlet valve is open and the piston moves downwards
due to which suction or vacuum is generated in the combustion chamber, that is, the internal pressure of
combustion is less than the atmospheric pressure due to which the fuel automatically It starts entering the
combustion chamber.

xi Fuel burning control Petrol fuel is a rapid ignition fluid. Its combustion can be controlled only by burning petrol
fuel slowly. Due to rapid combustion of petrol, there is a possibility of explosion and knocking in the combustion
chamber of the engine. Therefore, some additional substances are added to petrol to burn it slowly in the
combustion chamber.
The combustion of fuel in the engine can be controlled in the following manner: Octane rating: By increasing
the octane rating of petrol fuel, detonation in petrol is reduced.
Operational pressure: Combustion of petrol can be controlled by reducing the operational pressure in the
combustion chamber.
Air-fuel ratio: A balanced ratio of air and fuel can control the combustion of petrol in the combustion chamber.
Spark timing: The proper timing of sparking of the compressed fuel in the combustion chamber controls the
combustion of the fuel. Internal temperature: By reducing the internal temperature of the combustion chamber,
the combustion of fuel is controlled. is done.
xii Economic gain: Petrol should be of such a type that the vehicle can be operated for maximum kilometers in
one-liter quantity.

Study about carburetor fuel system and its components

such as fuel tank, mechanical fuel Pump, electrical pump,
fuel filters, carburetors and its circuits etc

Objectives: At the end of this lesson you shall be able to
• study about carburetor fuel system
• explain about fuel tank, mechanical fuel Pump & electrical pump
• demonstrate Circuits of Carburetor and Petrol filter.

Study about carburetor and its circuits
Carburetor: Carburetor is a device which takes petrol in liquid form from the fuel pump, vaporizes it with air,
mixes it in appropriate quantity and sends it to the cylinder through intake stroke of the engine.
Carburetor usually has three functions
1 Mixing

2 Vaporization
3 Atomization
Mixing: Mixing of air and petrol in the mixing chamber of carburetor with different speeds and loads is called
mixing.

Vaporization: The atomization of air and petrol which heats up and turns into vapor is called Vaporization.
Atomization: When a liquid is broken down into small particles it is called atomization and this helps in converting
the fuel into vapor.

Carburetor Circuit:
1 Float Circuit
2 Idle slow speed Circuit

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CITS : Automotive - Mechanic Diesel - Lesson 29 & 30