Four-Stroke Engine
An engine operating on a cycle which is completed in four strokes, or two revolutions of the crankshaft.
- The four strokes are:
- Induction Stroke - The stroke where the fuel-air mixture is drawn into the cylinder.
- Compression Stroke - The stroke of the internal Combustion Engine where the piston moves into the cylinder, compressing this fuel-air mixture to high density, pressure and temperature.
- Ignition - An electric spark then ignites the mixture and converts it into extremely hot burned gas.
- Working Stroke - The piston stroke during which the combustion gases exert a pressure on the moving piston.
- Exhaust Stroke - The piston stroke during which the exhaust gases are expelled from the cylinder ready for the next induction stroke.
Advantages:
- Last longer than two stroke engines
- More efficient than two stroke engines
- Pollute less than two stroke engines
Disadvantages:
- More complicated. Many more parts to break or go wrong.
- Half as powerful as two stroke engines (for equivalent engines)
- Fires once every two revolutions.
Bore and Stroke
The bore and stroke of the piston sets the swept volume. The ratio of bore to stroke is a good indicator of the engine characteristic such as how high it will rev and basic fuel economy. More simply it also defines some of the basic dimensions of the engine such as height and length.
Bore versus stroke for a number of production engines.
Historical Notes
- 1877 Four stroke internal combustion engine invented by Nikolaus Otto.
- 1890 First four-cylinder, four-stroke engine built by Wilhelm Maybach.
See also: Internal Combustion Engine, Petrol Engine, Two-Stroke Engine, Working Stroke.
Subjects: Automotive Engines