大学英语Lesson 4 Fuel System.ppt

Lesson 4 Fuel System The function of the fuel system is to store and supply fuel to the cylinder chamber where it can be mixed with air, vaporized, and burned to produce energy. The fuel, which can be either gasoline or diesel, is stored in a fuel tank. A fuel pump draws the fuel from the tank through fuel lines and delivers it through a fuel filter to either a carburetor or fuel injector, then delivered to the cylinder chamber for combustion[1]. 1 GASOLINE Gasoline is a complex blend of carbon and hydrogen compounds. Additives are then added to improve performance. The two most important features of gasoline are volatility and resistance to knock (octane). Volatility is a measurement of how easily the fuel vaporizes. If the gasoline does not vaporize completely, it will not burn properly (liquid fuel will not burn). If the gasoline vaporizes too easily the mixture will be too lean to burn properly. Since high temperatures increase volatility, it is desirable to have a low volatility fuel for warm temperatures and a high volatility fuel for cold weather. Resistance to knock or octane is simply the temperature the gas will burn at. Higher octane fuel requires a higher temperature to burn. Other factors that affect the octane requirements of the engine are: air/fuel ratio, ignition timing, engine temperature, and carbon build up in the cylinder. 1.1 FUEL TANK Tank location and design are always a compromise with available space. Fuel tanks today have internal baffles to prevent the fuel from sloshing back and forth. All tanks have a fuel filler pipe, a fuel outlet line to the engine and a vent system. All fuel tanks must be vented. Since 1970 all tanks are vented through a charcoal canister, into the engine to be burned before being released to the atmosphere. This is called evaporative emission control. 1.2 FUEL LINES Steel lines and flexible hoses carry the fuel from the tank to the engine. When servicing or replacing the steel lines, copper or aluminum must