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The two newest internal combustion engine technologies which have demonstrated the most promise in the last 25 years are the direct-injection stratified-charge (DISC) rotary engine [1] and the adiabatic diesel engine [2]. The (DISC) engine is particularly attractive for aviation applications [3] because of its light weight, multi-fuel capability and potential for low fuel consumption. However, one disadvantage with the DISC engine is the weight and size of the liquid cooling system. NASA Lewis Research Center has supported a technology enablement program to advance the DISC rotary engine for general aviation applications and recognizes the importance of improvement in fuel consumption and reductions in the coolant system weight [4].

The single stage rotary Wankel engine is difficult to convert into a diesel version having an adequate compression ratio and a compatible combustion chamber configuration. Past efforts in designing a rotary-type Wankel diesel engine resorted to a two-stage design. Complexity, size, weight, cost and performance penalties were some of the drawbacks of the two-stage Wankel-type diesel designs. This paper presents an approach to a single stage low compression ratio Wankel-type rotary engine. Cold starting of a low compression ratio single stage diesel Wankel becomes the key problem. It was demonstrated that the low compression single stage diesel Wankel type rotary engine can satisfactorily be cold started with a properly designed combustion chamber in the rotor and a variable heat input combustion aid. A 10.5 compression ratio rotary Wankel-type engine was started in 15 secs at −10°C inlet air temperature. High cranking speeds and white smoke were the biggest drawbacks of this design.