I'm a machining student, and for a project I'm making a nitro powered rotary engine to put on an RC car. I have the engine almost completely modeled, but I'm confused on the purpose of the combustion cavity on the rotary engine. Is it necessary for the engine to run or is it simply used to lower the compression ratio? If I can make an engine without the combustion cavity, I can get a compression ratio of 11:1, but creating the cavity drops the ratio to around 9:1-10:1 depending on the size of the cavity. Anyone who would know if this feature is necessary, please let me know. Thanks

 

the purpose is twofold. it can be used to manipulate compression ratio, but it also sort of functions as "the combustion chamber". it sort of controls the flame and helps drive the rotors.

i'm fairly sure i've seen some model rotary engines disassembled where the rotors did not have recesses. you should be fine without it.

 

I have seen some RC rotary engines, but nearly all of them lacked a combustion chamber.