Reciprocating piston designs that power the vast majority of internal combustion engines have several design shortcomings: low efficiency due to high friction and a limited revolution rate resulting in poor power density. Both the friction of piston/wall (due to piston side loading) and crank journal (due to maximum combustion pressure occurring at a locked crank state of TDC) and a limited RPM rate (due to forces of rapidly accelerating and decelerating pistons and valves) can be ameliorated in a rotating combustion arm type design.
The traditional reciprocating piston area path is turned into a circular combustion arm path as shown in Fig1. At the core, the engine has two gear synchronized rotors rotating in the same direction, each having two protruding block sections that sweep through a housing to form a compression and combustion stroke (exhaust and intake are handled by reciprocating valves). Fig2 shows the start of the compression stroke (1) with one block compressing air against the outer face of the second block which forms a compression chamber. Both blocks have sculpted faces to transition air (2) to the combustion chamber while continuing to compress it, at which point ignition would occur. At maximum compression (3), both blocks are aligned (equal to TDC on a reciprocating engine). The expansion stroke (4) is then carried out in the same fashion as the compression stroke.
As the rotors overlap in swept area, they are located facing each other shown in the exploded Fig4. Besides driving a synchronizing gear to ensure their precise alignment, they each drive an exhaust/intake valve. With the minimum of two rotors, this design achieves four power strokes per revolution (two simultaneously per block interaction).
Since the rotor blocks must seal against the housings as well as each other, sealing, as with all rotating designs, is a challenge. The three sides of the bock contacting the housing (the forth side is mated to the rotor) could be sealed using captured Wankel engine type apex seals, with careful lead-in provided at each transition. The rotor to housing interface could similarly be sealed with Wankel type face seals.