A 2-rotor, 11.6-liter rotary diesel engine was almost a thing

The rotary engine had its moment of automotive glory with Mazda, but while the Japanese automaker’s rotary engines where small-displacement, high-revving, buzz bombs, one American startup tried a very different approach, designing an 11.6-liter big-block rotary running on diesel for marine applications.

The company was Rotary Power International, and the engine was the Model 2116R. According to press materials dated August 2000 unearthed by Car Expert, the 2116R was a two-rotor engine with an aluminum block, 8.5:1 compression ratio, and a stratified direct injection system, as well as spark ignition. This would have allowed the 2116R to run on gasoline as well as diesel, or even kerosene or jet fuel, according to the company.

Rotary Power International quoted an output of 1,000 horsepower at 3,600 rpm and 1,550 pound-feet of torque at 2,400 rpm.

The company also discussed other, larger rotary marine engines, including the four-rotor, 23.1-liter 4231R and 6-rotor, 34.7-liter 6347R. These engines would have made 2,000 hp and 3,000 hp, respectively.

Rotary Power International Model 2116R rotary engine

The main advantage of a rotary engine, according to Rotary Power International, was power density. The company claimed its rotary engines achieved 2.5 pounds per horsepower, compared to four pounds per horsepower for contemporary marine piston engines. 

However, at $165,000 (in 2000 dollars), the 2116R was priced about $45,000 higher than a comparable piston engine, Rotary Power International acknowledged at the time. Like automotive rotaries, fuel economy wasn’t expected to be one of this marine engine’s strengths. It’s unclear if apex seals were a problem, too.

In the early 2000s, Rotary Power International talked up plans to use the 2116R in a “fast ferry,” but those plans seemingly fell apart. The company then proposed a hydrogen-powered rotary engine, and then a downsized engine called the Series 70. That apparently didn’t find any takers either, and the company appears to have dissolved sometime after 2005.

No automaker has sold a rotary-engined production car since the discontinuation of the Mazda RX-8 in 2012. Rumors of a Mazda rotary return have circulated since then, with the most recent reports claiming a rotary engine could be used as a range extender in future electric cars.

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