The science behind Rolls-Royce’s oddball four-rotor diesel rotary engine

This is the strangest engine you’ve likely never heard about. Back in the late 1960s and early ’70s, a number of automakers were experimenting with odd engine setups. Heck, that happens all the time, even today. This particular setup was quite odd, however, in that it was a diesel rotary. Making it odder still is that the automaker behind the madness was none other than Rolls-Royce.

Not only was Rolls-Royce experimenting with diesel burnt in rotary form, the British marque was making use of a quad-rotor setup. But the engine didn’t employ four rotors of the same size. For each pair of rotors, there was a small rotor above and a larger rotor located below. This means that the quad setup in use here was basically a doubled-up dual-stage rotary engine. 

The plan was to offer up this engine for military duty. Rolls-Royce is already well known for making aircraft engines, so spreading new engines to various markets wouldn’t be a strange business move. What’s weird is the engine itself. Even Mazda has to look upon this quad-rotor diesel drinker and take a step back.

Our friend Jason Fenske from Engineering Explained lays it all out for us in the video above. The larger rotors serve as forced induction units for the smaller rotors. In each chamber, a mixture of diesel and air is compressed below and then force fed to the rotor above. Jason goes into greater detail on how this mad motor worked. 

Sadly, this unique engine never made its way to production. Perhaps we’d be talking about a very different Rolls-Royce SUV if it had.

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