Power Unit
This chapter discusses internal combustion (IC) engines, the most commonly used
engines in automobiles today. The principle of operation, various types, and clas-
sification of IC engines are presented.
2.1.
Automobile Engines
Among all the automobile engines the gasoline (petrol)-fueled engine has dominated the
automobile field. In 1900 this power plant was in third position, behind the steam engine and
the battery electric system. The steam and electrically powered automobiles do not require a
transmission system due to availability of large power at low speeds. The greatest disadvantage
for these power units are respectively, the danger of high pressure in the steam boiler and the
inconvenience of recharging the batteries, which reduced their popularity. Chart 2.1 presents
the various automobile engines.
The gasoline engine, despite the necessity of transmission, has the advantage of producing
large amount of power from a small quantity of fuel that can be replenished easily. The diesel
engine was introduced due to its additional advantages, such as lower fuel costs, reduced
maintenance costs, low fire risk and more uniform torque over a wide range of speeds. Today
both gasoline and diesel engines are widely used in automobiles. However, they are greatly
responsible for harmful emissions that are causing environmental damage.
Automobile engines are called internal combustion (IC) engines because the fuel is burned
internally, or inside the engines. These are of two types, such as reciprocating and rotary. Almost
all the automobile engines today, using gasoline and diesel engines, are of the reciprocating
type. In these engines, pistons move up and down, or reciprocate. These engines are also called
piston engines. Rotary engines have rotors that spin, or rotate. Two general types of rotary
engines are the gas turbine and the Wankel engine. The Wankel engine is gaining popularity
for small automobiles. The gas turbine has been used more in buses and trucks.
The Wankel engine has some definite advantages over piston engines. It operates very
smoothly; it produces a lot of power for its size compared to same size reciprocating engines; it
can be muffled to operate very quietly because it has no noisy valve-train operation; and it
operates on low-octane gasoline and produces small quantities of nitrogen oxides emissions. But
other emissions are high and it does not operate as economically as the reciprocating engines
producing similar power.
The gas turbine produces high power for its size and weight as compared to reciprocating
automobile engines. It requires no cooling system or torque converter on the transmission. The
service life between overhauls is several times greater than the piston engine. It has low
hydrocarbon and carbon monoxide emissions. The latest designs have been able to reduce
nitrogen oxides emissions below the permissible value. The turbine engine operates best at a
steady speed, so it is more suitable for trucks and buses than for passenger cars.
Chart 2.1. Automobile engines.
