INTERNAL COMBUSTION ENGINE. DIESEL AND GASOLINE ENGINES

UNIT 3

The engine is the source of power that makes the wheels go around and the car move. The internal combustion engine converts heat into mechanical energy by burning a mixture of fuel and air within the cylinders or combustion chambers. The expansion of combustion gases is used for producing piston movement. This causes the crankshaft to turn or rotate. This rotary motion is transmitted to the driving wheels so the wheels rotate and the car moves. This burning, or combustion, takes place at a high speed above the pistons. The cylinder head is secured to the top of the cylinder block. It en­closes the cylinder block and forms the combustion chamber.

Internal-combustion engines are the most broadly applied power-generating devices. They can be classified by their application, type of fuel and method of its mixing with air, method of ignition, cylinder arrangement, strokes per cycle, cooling method, and valve type and location.

By the method of mixing fuel with air, there are engines with external mixing – carburetor engines and liquefied petroleum gas engines (LPG engines) and engines with internal mixing – diesel engines.

As to the type of fuel and the method of ignition there are spark ignition carburetor engines (SI-engines) and compression ignition diesel engines (CI-engines). A gasoline engine is that type of machine where power is generated within the cylinders. The engine is set in mo­tion by the explosions of a mixture of gasoline and air. A diesel engine is like a gasoline one but simpler. Diesel engines are usually larger and perform more work than gasoline engines as they give more power for each gallon of fuel burned. Besides they last much longer. Diesel engines use a cheaper kind of fuel than gasoline engines do. The fuel used in a diesel engine is oil. In diesel engines only air is blown into the cylinder on the charging stroke. The fuel is introduced in the form of spray and the engine requires no special ignition device (spark plugs). This air is compressed on the return stroke to a very high pressure. The compression pressure is much higher than that in any other engine. The result of the compression is that the air is heated to a high temperature. The compression ratio in the diesel engine is higher (15-20), the pressure (3.0-4.0 MPa) and temperature (600-700°C) are higher too. Such a high temperature of the compressed air is needed to ignite the diesel fuel injected into the cylinder. The heavy oil injected into the air at the end of the stroke is immediately ignited by the air temperature. The explosion pushes the piston down and turns the crankshaft. Diesel engines are more economical than their carburetor counterparts. As a result of their higher compression ratio, the diesel engines burn 25% less fuel (per a unit of work done). Diesel engines operate on heavy fuels that present less fire hazard in handling. The diesels, however, are more bulky, for the high pressure of combustion gases in the cylinder requires stronger engine components; they are more difficult to start, especially in cold weather.

1. Выпишите из словаря транскрипцию и перевод встречающихся в тексте слов:combustion, wheel, cylinder, chamber, method, carburetor, generate, gasoline, spark plug, compression ratio, ignite, cycle, mixture.