8.1. INTRODUCTION
Otto and Diesel cycle engines play an important role in our transportation and energy
use. They are typically reciprocating heat engines that convert the thermal energy from
fuel combustion to mechanical energy in the form of piston movement. The mechanical
energy further drives a vehicle over a distance. The Otto and diesel cycle engines are
the most common engine in passenger cars, light trucks, and other applications where
small (10 Hp) to medium power (500 Hp) is required. Some large turbo supercharged
radial aircraft engines reach 5,000 Hp. Applications of small power, such as
lawnmowers and hand-held devices like trimmers and chain saws, require a level of
100-1,000 W power. Typical values of their thermal efficiency are 30-35% for Otto
cycle engines and 30-40% for Diesel engines. Small utility-type engines may have
~20% efficiency due to simple design and control. While the basic principles of these
reciprocating engines have not changed significantly since invention, advances in fuel
induction, ignition systems, and exhaust emission controls have improved economy
and performance and reduced pollution.
