Rolls Royce made a diesel rotary engine with four rotors!

Rolls Royce Developed A 4 Rotor Diesel Wankel Engine.
It's as crazy as it sounds. Rolls Royce developed a diesel rotary engine for military applications. Because diesel engines require high compression ratios for compression ignition to occur, they used a second rotor to effectively multiply the compression ratio.

From the original Autocar article:
"The first Rolls—Royce development engine was the R1 which was conceived purely as a research tool. With a compressor stage of 1,126 c.c., and a combustion stage of 500 c.c., it produced over 50 bhp and achieved specific fuel consumptions of better than O.5lb/bhp/hour. Among other things, it was used to develop the best inter—porting arrangement between the two stages.

The R2 engine was the alternative three-stage layout, built but not investigated in detail. R3 refers to a combustion stage only, which is being used as a basic unit to build up a range of engines; it has a displacement of 1,216 c.c., and has produced 180 bhp at 4,500 rpm under test conditions.

The remaining engine of which details may be given is the 2—R6. This is a military engine formed of two banks of a two—stage engine. Each high pressure (combustion) stage has a displacement of 1,265 c.c., and is fed by a low-pressure stage of 3,250 c.c. The design power is 350 bhp at 4,500 rpm, for a weight of 939lb-a spectacular power-to-weight ratio for a diesel."