|An internal combustion engine burns a mixture of fuel and air. The most common type is a four-stroke, gasoline engine. A piston slides in and out of a cylinder. Two or more valves allow the fuel and the air to enter the cylinder and the gases that form when the fuel and air burn to leave the cylinder. As the piston slides back and forth inside the cylinder, the volume that the gases can occupy changes drastically.||
The power stroke is the only time when the gas does work on the engine.
|These four strokes repeat
over and over again. Most internal combustion engines have at least four
cylinders and pistons. There is always at least one cylinder going through the
power stroke and it can carry the other cylinders through the non-power
strokes. The maximum efficiency of such an engine is emax =(Tignition
- Tair)/Tignition where Tignition is the
temperature of the fuel-air mixture after ignition. To maximize the fuel
efficiency, you have to create the hottest possible fuel air mixture after
ignition. The highest efficiency that has been achieved is approximately 50% of
Link: The Otto Engine
engine is another type of internal combustion engine.
A gasoline engine takes in a mixture of gas and air, compresses it
and ignites the mixture with a spark. The fuel and air mixture
limits the compression ratio and therefore the temperature of the
fuel-air mixture. If the air is compressed to much then the
fuel spontaneously ignites and the engine "knocks". A diesel
engine takes in just air, compresses it and then injects fuel into
the compressed air. The compression ratio and therefore the
temperature can be much higher. The diesel engine uses less
refined fuel which ignites easier. It does not need a spark
plug, the heat of the compressed air lights the fuel spontaneously.
A higher temperature makes for a more efficient engine.
Link: The Diesel Engine
Link: Gasoline and Diesel Fuel