There are many types of fuel supply system in petrol engine. The basic fuel supply system in an automobile petrol engine consists of a fuel tank, fuel Lines, fuel pump, fuel filter, air cleaner, carburetor, intake manifold.
For the supply of fuel from fuel tank to engine cylinder following fuel feed systems are used:
- Gravity system
- Air pressure system
- Vacuum system (suction and gravity system)
- Pump feed system
- Fuel injection system
GRAVITY FUEL FEED SYSTEM:
In this system, the fuel tank is mounted at the highest point of the SI engine. this system is quite simple and cheap as the fuel drops into the float Chamber of the carburetor under Gravity. it is used in a small engine having low fuel consumption as sufficient head is not developed for large engine.
- The system is quite simple and cheap as of other fuel feed system
- The rigidity of placing the fuel tank necessarily over carburetor is its disadvantage
AIR PRESSURE FEED SYSTEM:
In this system, an airtight fuel tank is used and is placed under the seat or near the engine. the hand operated a pump or mechanically operated pump supplies the high-pressure air to the fuel tank for supply the fuel to the carburetor.
- The fuel tank can be placed at any suitable location
- There are chances of pressure leak within the chamber
VACUUM FEED SYSTEM (Suction and Gravity system:
In this system, fuel from the fuel tank which is placed near the engine is sucked by means of suction from the induction manifold. by means of gravity, the fuel is supplied to the float of the carburetor.
- The cost of the total system is less
PUMP FEED SYSTEM:
In this system, a steel pipe carries petrol to the fuel pump which Pumps it into the float Chamber of the carburetor through the pipe. here we use a mechanical or electrical or a diaphragm pump supplies the fuel from the fuel tank is placed at any suitable location and is vented to the atmosphere.
This system is used in most vehicles in the present days.
FUEL INJECTION SYSTEM:
The petrol injection system now comes to modern vehicles. the fuel is atomized by means of an air injector nozzle then delivered into an air stream. there may be separate fuel injectors are used for separate cylinder or one single fuel injector is used.
- This is the most accurate fuel supply system
- High power is developed
- It has quick starting and warms up
- Low specific fuel consumption rate
- Back-flow of petrol may take place
- High initial cost
THE COMPONENTS OF FUEL SUPPLY SYSTEM:
The fuel tank holds the fuel for the engine. It is made of steel or aluminum or synthetic rubber compounds and fiber reinforced plastics which are flame resistant. And these tanks are coated with lead-tin alloy to protect the tank from the corrosion effect.
This tank is placed in any suitable position of a vehicle. For front engine vehicle, the fuel tank is in the underside of a luggage compartment at the rear end or directly above the rear axle, and for rear engines, the fuel tank is placed in the front behind the compartment.
There are a couple of baffle plates inside the fuel tanks because of when brakes are applied to the vehicle the fuel surge inside the vehicle or when a car turn around then also fuel surge inside the tank so this baffle plate helps to reduce the surge of fuel inside the tank. These plates divide the tank in a number of the compartment which is interconnected through a pipe.
Petrol is filled by the small opening cap. A filter is placed at the tank end of the fuel line and a small hole is provided for vented to the atmosphere
A drain plug is fitted at the bottom of the tank to remove sediments and the fuel tank is also provided with a fuel gauge sensing unit for checking of fuel level inside the tank.
- It is used to store the fuel.
The fuel pump is used to deliver the fuel from the fuel tank to the carburetor.
There are generally two pumps are used:
- A.C. Mechanical Pump
- S.U. Electrical pump
- It supplies the high-pressure fuel from tank to the carburetor.
These tubes are used for connects the fuel tank with the pump and pump to the carburetor. Generally, these tubes are made of Copper or Steel.
The two joints of the tubes are made flexible because of the flexible joints help the fuel tank to moves back or front with the body, and also pump is moves according to the body. This joint prevents the loosening of fuel line by front-back movement of the body.
- These pipeline helps to deliver the fuel from the fuel tank to pump and to the carburetor.
This is very necessary for an engine to get fresh air, otherwise, the polluted air causes several damages to the engine chamber. Particularly Piston, Piston chamber, Piston ring, and Valves. And if the polluted air enters the crankcase where we store engine oil that can be damaged the lubrication parts like bearings. Therefore we need to install an air filter which purifies the air before entering the engine cylinder.
This can also act as a silencer for the carburation system and also as a flame arrester when the engine has backfired.
The air filter will clean regularly. If you don’t clean it can cause much fuel consumption, and reduce the engine efficiency.
The air cleaners generally used are two types:
- Heavy duty types air cleaner
- Light duty types air cleaner
- It used to clean the air.
A fuel filter is necessary for a vehicle to clean the fuel.
For this, a very affected device is used and that is chamois leather, which only allows to passing the petrol into it and the water is intercepted by this. And also fine particles can not pass through it.
- It is screened off the dirt or foreign matter from the fuel and prevents entry to the pump.
Fuel gauge unit:
A fuel gauge is an instrument which is fitted to the dashboard of the vehicle so that driver can know the amount of fuel inside the fuel tank.
- It indicates the fuel level in the tank.
A perfect air-fuel mixture is necessary for a petrol engine to run. So, therefore, we use a carburetor. It is device which controlled the air-fuel mixture.
There are two chambers in carburetor one is float chamber which is used to maintain the fuel level with the help of needle valve and another one is mixing chamber where the mixture of air-fuel takes place.
The air-fuel ratio in the carburetor is about 15: its mean 15 kg of air has sufficient oxygen to burn 1 kg of petrol.
Also read Boiler mountings and accessories
LAYOUT OF THE FUEL SUPPLY SYSTEM IN S.I. ENGINE: