You may ask yourself, ``If the Wankel engine is so great, why isn't it still in use in consumer autos?'' There are two reasons.

The first is durability. For the proper operation of the combustion cycle, the chamber created between the rotor and the housing must be perfectly sealed. The problem is that, since the rotor barely brushes the housing, and does so only at three locations, there is little tolerance for error. Thus, normal wear and tear to the rotor and housing will relatively quickly lead to an incomplete seal, which is bad. Pistons last longer because they have a much better seal.

Second is fuel efficiency and emissions. Because the chamber has an odd triangular shape, fuel and air pulled into chamber in the intake stroke do not get mixed evenly within the chamber (i.e., there is bad swirl). Thus there is, compared to the reciprocating engine, a larger amount of fuel left incompletely burned. Thus, not only are you getting less energy out of each unit of fuel injected into the engine; but you are also emitting more unburned gunk, which is bad for the environment (and, incidentally, for emissions standards).

A friend of mine (Carl Arthur), who is a mechanical guru, had the idea of making a rotary diesel engine. This, he claims, would solve or at least ameliorate these problems. As far as the first problem goes, diesel fuel is thick enough to serve as a lubricant, thus reducing wear. As for the second problem, the injection valves atomize the fuel pretty thoroughly, giving you enough surface area to ensure a relatively clean burn. I do not know whether the peculiar operation of the Wankel engine is incompatible with the diesel cycle, or if there is another reason such engines are not made.


Stewacide informs me that a rotary engine may have problems providing the higher compression ratio that diesel engines require. I'll have to get back to Carl on this one.