1. Two Stroke Internal Combustion Engines
*How a two stroke engine works
*Advantages/Disadvantages
From foukeffa.org
GA Ag Ed Curriculum Office
To accompany Georgia Agriculture Education Curriculum Lesson
July 2002

2. About this lesson.
This lesson contains hypertext links to
If you are connected to the internet, click on the link icon and scroll to the animation at the sight.

3. Introduction to the Two Stroke Engine
This type of engine is commonly found in applications such as;
lawn and garden equipment
dirt bikes
small outboard motors

4. Introduction to the Two Stroke Engine
Two stroke engines have advantages over four stroke:
simplified construction (no valves)
fire once every revolution for a significant power boost
Great power to weight ratio

5. The two stroke cycle
The two stroke engine ignites every revolution of the crankshaft. These engines overlap operations to reduce parts while maintaining power.

6. The two stroke cycle
After the fuel air explosion, the piston is driven down. As the piston reached the bottom of it’s stroke, the exhaust port is uncovered. Most of the gases are driven out.

7. The two stroke cycle
When the piston has bottomed out, the intake port is uncovered. The new fuel enters and is ready for compression and combustion.

8. The two stroke cycle
When the fuel mixture is being compressed a vacuum is created in the crankcase. The vacuum opens a reed valve and sucks air/fuel/oil in from the carburetor.

9. The two stroke cycle Simply put, in a two stroke engine you have only:
Compression
Combustion
Thus, Two Strokes.

10. 2 stroke compared to 4 stroke
In two stroke engines the crankcase is a pressurization chamber to force fuel/oil/air into the cylinder. Here you mix oil and gas to lubricate internal parts.
In four stroke engines the crankcase is separate from the compression chamber. This allows the use of heavy oil for lubrication.

11. Disadvantages of a two stroke
The engines do not last as long due to poor lubrication.
You have to mix two cycle engine oil with gasoline. $$$$$
The engines do not use fuel efficiently.
These engines produce a lot of pollution.

12. Summary
Two stroke engines are great for the power to weight ratio and their simple design, however, due to there pollution concerns these engines will be harder to find.

13. Source