Classification of Engines

Principles of the Authomotive Engines
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cylinder arrangement. They all operate on the same basic principles, and are

constructed to meet the needs of the system it will be used for.

a. Fuel.

(1) Gas. A hydrocation, obtained from petroleum, that is suitable as

(2) Diesel. The substance that is burned to produce heat and create

motion of the piston on the power stroke in an engine.

b. Cooling. Engines are classified as to whether they are air or liquid

cooled. All engines are cooled by air to some extent, but aircooled engines

are those in which air is the only external cooling medium. Lubricating oil

and fuel help cool engine parts, but there must be an additional external means

of dissipating the absorbed heat.

(1) AirCooled. Aircooled engines are used extensively in military

vehicles as well as in aircraft. This type is used where there must be an

economy of space and weight. It does not require a radiator, water jacket,

coolant, or a pump to circulate the coolant. The cylinders are cooled by

conducting the heat to metal fins on the outside of the cylinder walls and

head. To effect the cooling, air is circulated between the fins. When

possible, the engine is installed so it is exposed to the air stream of the

vehicle; the baffles direct the air to the fins. If the engine cannot be

mounted in the air stream, a fan is used to force the air through the fins.

(2) LiquidCooled. Watercooled engines require a water jacket to hold

the coolant around the valve ports, combustion chambers, and cylinders; a

radiator dissipates the heat from the coolant to the surrounding air; and a

pump circulates the coolant through the engine. Watercooled engines also

require a fan to pass air through the radiator because the speed of the vehicle

does not always force enough air through the radiator to provide proper

c. Valve arrangement. Engines may be classified according to the

position of the intake and exhaust valves; that is, whether they are in the

cylinder block or in the cylinder head. Various arrangements have been used,

but the most common are Lhead, Ihead, and Fhead. The letter designation is

used because the shape of the combustion chamber resembles the form of the

letter identifying it.

OD0610

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