| Overview | Intro |
| Concepts | Illustrated |
| Side View | Operation |
| Single Chamber | Rotary vs. Piston |
| Pollution | Seals |
| Applications |
To quote from Wikipedia:
| Generally internal combustion engines, particularly reciprocating internal combustion engines, produce moderately high pollution levels, due to incomplete combustion of carbonaceous fuel, leading to carbon monoxide and some soot along with oxides of nitrogen & sulfur and some unburnt hydrocarbons depending on the operating conditions and the fuel/air ratio. The primary causes of this are the need to operate near the stoichiometric ratio for petrol engines in order to achieve combustion (the fuel would burn more completely in excess air) and the "quench" of the flame by the relatively cool cylinder walls. |
In the piston engine, the fuel is injected slightly before the engine reaches maximum compression. If combustion occurs right after the fuel is injected, the engine will "knock" because the force exerted on the piston by the exploding fuel is directed against the rotation if the crankshaft. Instead of with the rotation of the crankshaft, the prematurely exploding fuel slows slows the engine down, robs power, and can damage the engine. To keep this from happening, the fuel must be blended with an anti-knock compound, and even then it is likely to happen if the engine is operated with a heavy load at low speed.
The fuel is injected before maximum compression in order to take full advantage of the 25% of the engine cycle that can be used to generate power.
In the rotary engine, around 90% of the engine cycle is available for power generation, so it is not as critical for fuel to be injected early. Thus there is no problem if the fuel ignites as soon as it is injected. The engine can be run with a leaner mixture leading to more complete ignition.
The "quench" of the flame by relatively cool cylinder walls might be more pronounced in the rotary engine. Since the rotary combustion chamber is not cylindrical, it would have more surface area per unit volume. This would be mitigated by the larger combustion chambers in the rotary engine. The square cube law dictates that making the same shape larger gives a smaller surface area to volume ratio because the volume increased as the cube of the linear dimensions and the surface area increase as the square of the linear dimensions.
The fact that a rotary engine does not need a fuel additive would greatly reduce it's polluting effect.
Since the rotary engine can auto start after a short period of non-use, the engine could be shut down while waiting for a stoplight, or traffic, etc. That would be a great boon to urban areas where such delays are more common and where pollution is more of a problem.
Combustion at higher temperatures produces more nitrogen oxides. Higher compressions mean higher temperatures, so the low-compression rotary engine should produce fewer nitrogen oxides.