A Clean Lightweight Engine
It is only a matter of time until 2-stroke engines
will be banned, because there are no further options to reduce their emissions.
Especially the amount of unburnt hydrocarbons is much too high.
But in some areas the most common alternative, a 4-stroke reciprocating piston engine,
only meets market requirements insufficiently, because it generally has a worse
power-to-weight ratio and a more narrow power band. For example the regulations for 4-stroke engines in karting have been widely
released, probably with the insight that the engines on the market are no true
alternative to the existing 2-stroke racing engines.
Contrary to this, the power-to-weight ratio of a Wankel rotary engine exceeds that of the 2-stroke engine. Due to the processes within the engine, especially the long timings and high exhaust temperature,
any oil entering the combustion chamber burns almost without residue. Despite the good power-to-weight ratio this leads to very favourable emissions, which can be as low as 1% of comparable 2-stroke engines and reach best 4-stroke levels in the driving cycle.
A rotary engine with fuel lubrication can be operated with a (unregulated) catalytic converter.
Production cars like the Mazda RX-8, which are operated with a separate oil supply, meet
current automotive emission standards and can even be operated with hydrogen.