Many "purists" argue that the spark assisted heavy fuel Wankels shown at Oshkosh
were not true "Diesels". The Diesel Cycle really has nothing to do with
compression ignition, the distinction being "constant pressure heat addition" That
means that fuel is injected over a period of time where the piston is moving away
such that the heat expansion is roughly matched by the increasing volume. This is
a less efficient cycle than the "Otto" where the description is  "constant volume
heat addition"  (IE the air/fuel mixture goes off with a bang while the piston is
stopped at TDC - which of course, is fortunately not true) Both engines operate on
a bastardized combination of the two cycles. In practice the "Diesel" provides
greater efficiency by the nature of the higher compression ratio (really higher
expansion ratio), which it both requires and permits. The full charge is not
present during the critical compression heating, so it does not destructively pre
ignite. Particularly at low power levels enough of the fuel is present in the
Diesel to accumulate, vaporize, and spontaneously ignite for the famous Diesel
"rattle". Virtually any direct injection engine can fulfill these requirements
with virtually any octane of cetane  rating, with a proper relationship of
injection and spark timing, and exploit low octane fuels at high compression
(expansion) ratios -  Almost any type of engine can be made to run on kerosine, or
almost any fuel. Vance

This is the prechamber on the jet A burning PATS apu based on the Norton Wankel.

Paul Lamar
 
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