Fuel Supply System of Gasoline Engine(UNIT SEVEN)All the gasoline engines have substantially identical fuel systems and run on a mixture consisting of fuel vapor and air. The fuel system comprises the units designed to store, clear and deliver fuel, the units intended to clean air and a unit for preparing a mixture from fuel vapor and air.In a fuel system different components are used to supply fuel from the fuel tank into the engine cylinder. Some of the important components are fuel tank, fuel pump, fuel filter, carburetor, intake manifold and fuellines or tubes connecting the tank, pump and the carburetor.The fuel tank is a fuel container used for storing fuel. It is made of sheet metal. It is attached to the vehicle frame with metal traps and is located at the rear of the vehicle. They are mounted in a boot or boot-floor pan in case of front-engined cars and small commercial vehicles. In order to strengthen the tank as well as to prevent surging of fuel when the vehicle rounds a curve of suddenly stops, baffle plates are attached to the inside of the tank.A cap is used to close the filler opening of the tank. The fuel line is attached at or near the bottom of the tank with a filtering element placed at the connection. The other components of the fuel tank are the fuel gauge sending unit, a vent pipe, receiving unit. To prevent the dirt and water from entering the luggage compartment, a sealing strip is fitted between the fuel tank and boot floor pan. Moreover to limit the transmission of frame distortion to the tank giving rise to squeaking as the metal parts get rubbed together, rubber or felt pads are often fitted between the mountings and the tank. Provision is also made against drumming of the tank by these mountings. The tank may be placed at the side of the chassis frame for convenience in case of large commercial vehicles. The length of the connecting lines or tubes from the tank to the carburetor is also restricted by this at the same time.A porous filter is attached to the outlet lines. By drawing fuel from the tank through the filter, any water in the bottom of the tank as well as any dirt into the fuel gathers on the surface of the filter. To keep the fuel always under atmospheric pressure, the filter pipe or tank is vented.In order to prevent dirt in the fuel from entering the fuel pump or carburetor, fuel filters and screens are used in the fuel system. If the dirt is not removed from the fuel, the normal operation of these units will be prevented. The engine performance will also be reduced.The filter is either fitted inside the fuel tank and pump or operates as a separate unit connected between the fuel tank and pump or between pump and carburetor into the fuel lines. Carburetors are also provided filter screens while a filter element is provided in the fuel tank.The fuel filter used is generally a sediment bowl made of glass or metal and a strainer screen. When the fuel drawn from the tank passes through the filter (through the bowl and strainer screen), particles of dirt and water settle in the bottom of the bowl. In certain vehicles, a separate filter either of the disk or ceramic type is used. It is either located between the fuel pump and carburetor or in the fuel line.For connecting the fuel tank to the fuel pump, metallic tubes or synthetic rubber hose used are called fuel lines. They are usually positioned with metallic clips along the frame side members. The tubing or fuel lines are also used to connect fuel pump to the carburetor. In order to absorb vibration as well as prevent breakage of the fuel lines, a short flexible line is used between the fuel pump and the tank.In order to meter and caution the driver of the motor vehicle about the quantity of fuel consumed and left in the tank, a fuel gauge is used. It is generally fitted on dash board for easy reading of the fuel. It is usually a balancing coil type having construction similar to that of an oil gauge. It is generally electrically operated.It consists of a sending unit mounted on the fuel tank and a receiving unit having a caliberated gauge mounted on the instrument panel.A sending unit consists of a float controlled thermostat or variable resistor. With a float and the float arm extending into the fuel tank, the whole unit is mounted on it. The level of fuel in the tank varies the position of the float. The amount of electrical resistance within the variable resistor for controlling the amount of current sent to receiving unit on the instrument panel is determined by the float position.The receiving unit mounted on the dash board indicates the amount of fuel in the tank on a caliberated gauge by the amount of current received from the sending unit.On modern automobiles, two types of fuel gauges; thermostatic type and an electromagnetic type are used.In order to prevent the rapid wear and tear of engine operating components causing reduced performance air cleaner is fitted to the carburetor air intake, it is mounted on thecarburetor air-horn for trapping dirt. Before entering the carburetor, the air must pass through it.To reduce the noise produced by the air rushing into the carburetor, a silencing chamber is built into the air cleaner. In case the engine misfires back through the carburetor, it acts as the flame arrestor.There are in general three types of the air cleaners used in modern automobiles. They are (a) oil bath cleaner (b) oil-wetted mesh air cleaner (c) dry type air cleaner. The first two are also known as heavy duty air cleaner while the third is known as light duty air cleaner.Fuel pumps are the devices used to supply fuel from the fuel tank to the carburetor. There are in general two main types of fuel pumps used in automobiles. They are main types of fuel pumps used in automobiles. They are (a) mechanical fuel pump (b) electric fuel pump.汽油发动机的燃料供给系统所有的汽油发动机具有基本相同的燃料系统和运行的燃料蒸气和空气组成的混合物中。