Torque: Rotary Diesel No Pistons Needed

Diesel Power|December 2019

Torque: Rotary Diesel No Pistons Needed
Building a diesel engine that does not use traditional pistons may seem odd, but in today’s modern age of high efficiency, low emissions, and weight reduction, an engine with a nonconventional rotor may be the key to things to come.

A compression-ignition rotary powerplant is not a new concept; the idea dates back to around the same period when the first Wankel rotary gas engine was developed (Felix Wankel’s first working prototype was 1957). Sharing a basic design with its gas brethren, the Wankel diesel powerplant uses a triangular-like rotor in an oval epitrochoid-shaped housing. This design offers the proposition of an efficient engine with low mass and smooth operation.

The problem that has kept the engine from coming to fruition is the design of the Wankel rotary’s combustion chamber, which is elongated and convex. This shape makes it hard to get compression high enough for proper ignition, without excessive heat loss. A source of charged air is needed, but crankshaft or exhaust-driven superchargers draw too much power to be efficient. So, using externally fed compressed air is the only way to get the engine to function. Wankel conceptualized an external supercharger to try to solve the problem. Another issue with the design is getting the combustion chamber correctly angled toward the injection nozzle for a proper air/fuel mixture.

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December 2019