An internal combustion engineis operated by liquid or gaseous fuel. Actually, gaseous fuel is most useful due to high octane rating, less deposit trouble, and clean operation but the use of this type of fuel is mostly restricted to those areas where gas is available. It is also quite difficult to carry gas for automobile purpose. However in many metro cities compressed natural gas (CNG) is available and many vehicles are running on it.
Still today liquid fuels, obtained from Petroleum (Crude Oil) are used to the largest extent primarily because of large quantities of energy per unit volume and the ease of handling, storing and transportation. This type of fuel has some engineering disadvantages as like, vaporization, atomized or at least partly vaporized during the process of mixing.
What is the fuel supply system in a petrol engine?
This system in petrol engine mainly consists of below parts,
The fuel can be supplied to the petrol engine under gravity or under pressure.
In the gravity system, the fuel flows to the engine under gravitational force as the fuel storage tank is placed at a higher level than cylinder head. In this system fuel pump is not required.
In pressure system, the fuel from the fuel tank is forced by the fuel pump through the filter to the carburetor. In this case, the fuel tank is placed at a lower level than the petrol engine head and sometimes away from the petrol engine. For example, motor cars, trucks etc. By keeping the fuel tank away from the hot engine, we can avoid the chances of catching fire in the event of an accident.
In a fuel system for a petrol engine, the fuel storage tank is located well below the carburetor. The fuel is supplied by the fuel pump to the carburetor through the fuel filter which removes the dirt and other foreign particles from the petrol. This system is extensively used for motor cars.
Description of some parts used in fuel supply system.
01) Fuel Pump
A diaphragm type fuel pump is used in petrol engines as there is no need of extra high pressure of fuel. This fuel pump is extensively used to pump the fuel from fuel tank to the carburetor in the automotive engines. A flexible diaphragm is moved down against the force of the diaphragm spring by the diaphragm lever and the operating arm which is actuated by the camshaft eccentrically.
The pressure falls in the pump chamber and so the fuel from the fuel tank flows through the fuel inlet valve. Fuel inlet valve closes at the return stroke as diaphragm spring forces the diaphragm upwards, same time fuel outlet valve opens and thus the fuel starts flowing from the pump to the carburetor.
02) Fuel Filter
To get rid of unwanted dirt, filters are used. A filter used to clean the air is known as air filter, to clean fuel, is known as fuel filter, to clean lubricating oil, is known as oil filter. In filters, paper elements, cloth elements, felt elements and the combination of felt and cloth elements are used. Basically there are two types of fuel filters used,
a) Preliminary fuel filter
b) Secondary fuel filter.
This is the device which mixes the fuel with air and supplies this mixture to induction manifold of the petrol engine. The carburetor controls the required quantity of fuel and breaks up into minute globules for being mixed with the correct quantity of air. Types of carburetor are
a) Zenith carburetor
b) Solex carburetor
c) Amal carburetor
The details of each part will be covered in coming posts.