internal-combustion engine: The Two-Stroke Cycle

The two-stroke engine is simpler mechanically than the four-stroke engine. The two-stroke engine delivers one power stroke every two strokes instead of one every four; thus it develops more power with the same displacement, or can be lighter and yet deliver the same power. For this reason it is used in lawn mowers, chain saws, small automobiles, motorcycles, and outboard marine engines.

However, there are several disadvantages that restrict its use. Since there are twice as many power strokes during the operation of a two-stroke engine as there are during the operation of a four-stroke engine, the engine tends to heat up more, and thus is likely to have a shorter life. Also, in the two-stroke engine lubricating oil must be mixed with the fuel. This causes a very high level of hydrocarbons in its exhaust, unless the fuel-air mixture is computer calculated to maximize combustion. A highly efficient, pollution-free two-stroke automobile engine is currently being developed by Orbital Engineering, under arrangements with all the U.S. auto makers.

Sections in this article:

• Introduction
• Evolution of the Internal-Combustion Engine
• Environmental Considerations in Engine Design
• Cooling and Lubrication of Engines
• The Two-Stroke Cycle
• The Four-Stroke Cycle
• Rotary Engines
• Reciprocating Engines
• Bibliography

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.

See more Encyclopedia articles on: Technology: Terms and Concepts