CLASSIFICATION OF ENGINES

LEARNING OBJECTIVE: Recognize the differences in the types, the cylinder arrangements, and the valve arrangements of internal combustion engines.

Engines for automotive and construction equipment may be classified in a number of ways: type of fuel used, type of cooling used, or valve and cylinder arrangement. They all operate on the internal combustion principle, and the application of basic principles of construction to particular needs or systems of manufacture has caused certain designs to be recognized as conventional.

The most common method of classification is by the type of fuel used; that is, whether the engine burns gasoline or diesel fuel.

ENGINE COMPARISON

Mechanically and in overall appearance, gasoline and diesel engines resemble one another; however, in the diesel engine, many parts are somewhat heavier and stronger, so they can withstand higher temperatures and pressures that the engine generates. The engines differ also in the type of fuel used and how the air-fuel mixture is ignited. In a gasoline engine, the air and fuel are mixed together in a carburetor or fuel injection system. After this mixture is compressed in the cylinders, it is ignited by an electrical spark from the spark plugs.

A diesel engine has no carburetor. Air alone enters the cylinder where ii is compressed and reaches a high temperature due to compression. The heat of compression ignites the fuel injected into the cylinder and causes the air-fuel mixture to burn. A diesel engine requires no spark plugs; the contact of diesel fuel with hot air in the cylinders causes ignition. In a gasoline engine, the heat from compression is not enough to ignite the air-fuel mixture, so spark plugs are required.