April 2020 | BlogMech

Carburetor: Carburetion is the process of measuring, mixing and supplying to a spark ignition engine continuously a suitable combustible mixture of fuel and air. This mixture supply must be in accordance with the engine speed and load requirements. The carburetor supplies this mixture to an engine. The carburetor consists basically of a float chamber and a metering cum mixing chamber.

Fuel feed system of carburetor engines

The preparation of air fuel mixture and its supply to the cylinders of the carburetor engine, the adjustment of its quality and quantity are accomplished by the fuel feed system. The feed system operation has a large effect on all the principal engine parameters. Therefore, necessary care must be taken to keep this system in proper working order during the engine use.

The system has a storage tank with fuel level amount sensing element, fuel gauge, filter, pump for supplying fuel from tank to carburetor. The fuel tank cap is vented. The atmospheric air enters the carburetor via air filter which acts at the same time as an intake silencer. From the carburetor, the fuel air mixture is supplied to the cylinder via intake duct.

Fuel gauge

An electric gauge with balanced coils is used in many cars for indicating the quantity of fuel available in the fuel tank. The gauge is mounted on the instrument panel in front of the driver. This type of electric fuel gauge consists of two units a dash unit and a tank unit.

Fuel strainer

Some of the fuel tanks include a fuel filter at their exit or a sump at the bottom, to collect dirt and water and prevent them from reaching the pump and carburetor. Some tank are provided with a drain plug on the bottom for emptying the tank. Fuel tanks are often provided with vertical baffles to prevent surging of the fuel.

An additional fuel strainer is usually placed in the fuel line either before the pump as shown in the picture or after pump to filter gasoline before it enters the float chamber. The unit serves to catch any water or foreign particles that were not filtered out previously, in the fuel tank filter unit. One type of filter is shown in the picture. The fuel that enters into the glass bowl, passes through a ceramic filter to reach the inside section that is connected with the exit. The water and sediment are collected in the bowl which is made removable for cleaning.

Some engines use a disposable fuel filter in the fuel feed system. The entire unit may be replaced whenever it becomes inoperative, simply by loosening snap clamps.

Posted in: Carburetor Fuel Feed System, components of fuel feed system, Fuel Feed System of Carburetor Engines, Fuel gauge of a carburetor, Fuel strainer of a carburetor, functions of a fuel feed system, parts of a carburetor, working of a fuel feed system.

Automobile Engineering

Valve Timing Diagram | Valve Timing Diagram for Four-Stroke Petrol Engine | Valve Timing Diagram for Four-Stroke Diesel Engine

By magnaparthi on 30/04/2020

We consider that the valves open and close at the dead centre positions of the piston. But, in actual practice they do not open and close instantaneously at dead centres. The valves operate some degrees before or after the dead centres. The ignition is also timed to occur a little before the top dead centre. The timings of these sequence of events can be shown graphically in terms of crank angles from dead centre position. This diagram is known as valve timing diagram.

Valve timing diagram for four-stroke petrol engine:

diagram shows the valve timing diagram for a four-stroke cycle petrol engine. The inlet valve opens 10-30° before the top dead centre position. The air-fuel mixture is suked into the engine cylinder till the inlet valve closes. The inlet valve closes 30-40° or even 60° after the bottom dead centre position. The air-fuel mixture is compressed till the spark occurs.

The spark is produced 20-40° before the t.d.c. position. This gives sufficient time for the fuel to burn. The pressure and temperature increases. The burning gases expand and force the piston to do useful work. The burning gases expand till the exhaust valve opens. The exhaust valve opens 30-60° before the b.d.c. position. The exhaust gases are forced out of the cylinder till the exhaust valve closes. The exhaust valve closes 8-20° after the t.d.c. position. Before it closes, again the inlet valve opens 10-30° before the t.d.c. position. The period between the inlet valve opening and exhaust valve closing is known as valve overlap period. The angle between the inlet valve opening and exhaust valve closing is known as angle of valve overlap.

Valve timing diagram for four-stroke diesel engine:

The actual valve timing diagram for four-stroke diesel engine is shown in figure The inlet valve opens 10-25° before the top dead centre position. Fresh air is sucked into the engine cylinder till the inlet valve closes. The inlet valve closes 25-50° after the bottom dead centre position. The air is compressed till the fuel is injected. The fuel injection starts 5-10° before the t.d.c. position in the compression stroke. The air fuel mixture burns. The temperature and pressure increases.

The burning gases expand till the exhaust valve opens. The exhaust valve opens 30-50° before the b.d.c. position. The exhaust gases are forced out of the engine cylinder till the exhaust valve closes. The exhaust valve closes 10-15° after the t.d.c. position. Before the exhaust valve closes, again the inlet valve opens 10-25° before the t.d.c. position. The period between the inlet valve opening the exhaust valve closing is known as valve overlap period. The angle between these two events is known as angle of valve overlap.