This paper describes the development and characterisation of small-scale rotary engines with displacements in the range of 781500 mm for portable applications in the range of 10200 W of power output. Small-scale combustion engines present a number of research challenges including manufacturing tolerances, sealing, thermal management, ignition, combustion efficiency and porting. Four engines have been characterised using a custom test bench and show an increase in performance due to design changes that mitigate the challenges associated with small-scale engines. The volumetric power density has been increased from 11 W/cm in a 348 mm engine operating with a supercharged hydrogen/air mixture to 22 W/cm in a 1500 mm engine operating with naturally aspirated liquid hydrocarbon fuel. The thermal efficiency has also been increased from 0.2 to 4%. Continued improvements in sealing, thermal management, combustion efficiency and friction reduction will allow further increases in engine performance.
Keywords: small-scale rotary engines, meso-scale combustion, portable power, manufacturing tolerances, sealing, thermal management, ignition, combustion efficiency, porting, friction reduction, engine performance