2.2.
Automobile Engines Classification
Automobile engines are classified in many several different ways as follows :
(i) Types of Cycles : Two-stroke and four-stroke cycles. For details section 2.3 may be
referred.
(ii) Types of Fuel Used: Gasoline (petrol) and diesel. For details chapter 8 may be referred.
(Hi) Number of Cylinders : Passenger-car engines generally have three, four, five, six,
eight and twelve cylinders. Twelve and sixteen cylinder engines have been used in buses and
trucks.
(iv) Arrangement of Cylinders : The automobile engines vary according to the arrange-
ment of cylinders in the cylinder block. Refer section 2.5 for details.
(v) Firing Order : Firing order is the order in which the cylinders deliver their power
strokes. This is a built-in part of the engine design. The strokes are divided along the crankshaft
so that a well distributed pattern results, minimising the strain on the crankshaft. For finding
firing order, manufacturers’ service manual for the engine is to be consulted. For firing order
details, section 2.6 may be referred.
(vi) Arrangement of valves: Engines may be classified according to the location and type
of valve system employed. Refer section 2.7 for detail.
U”w> Type of Cooling : Most automobile engines use a liquid, usually water mixed with
antifreeze, to maintain the engine at a constant operating temperature by transferring heat
from the metal surrounding the combustion chamber to the liquid. This system is called a liquid
cooling system. Some automobiles transfer the heat directly to the air without an intermediate
liquid cooling medium. Cooling the engine by this method is called air cooling. For further details
chapter 12 may be referred.
wiii) Reciprocating or Rotary Engines: Rotary engines are rotating combustion cham-
ber engines (Wankel engine) and turbines. Rotary engines have been discussed in chapter 5.
