OTTO AND DIESEL CYCLES

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.