2. Classification of Engines. Automotive engines may be classified according
to the type of fuel used, type of cooling system employed, or valve and
constructed to meet the needs of the system it will be used for.
(1) Gas. A hydrocation, obtained from petroleum, that is suitable as
(2) Diesel. The substance that is burned to produce heat and create
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
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
letter identifying it.