Performance explorations of a naturally aspirated opposed rotary piston engine fuelled with hydrogen under part load and stoichiometric conditions using a numerical simulation approach

Highlights: • Few studies are available for hydrogen fuelled opposed rotary piston engines. • This engine is characterized by high power density and simple structures. • Impacts on engine performance by engine load are investigated in detail. • Engine power density and exhaust energy loss are higher than reciprocating engines. • Performance changes by engine load significantly depend on the engine speed. Opposed rotary piston (ORP) engines are characterized by high power density, compact designs, and smooth operations which meet the requirements of the power source for hybrid vehicles. Hydrogen fuel applications will fully present ORP engines' advantages due to the short cyclic period. Internal combustion engines mainly operate under part load conditions over real world driving, the performance of hydrogen ORP engines over part load needs to be addressed in order to promote the applications to hybrid vehicles. In this paper, combustion and nitrogen oxides emission of this ORP engine under part load and stoichiometric conditions were investigated using a 3D numerical simulation approach. The results indicated that peak in-cylinder pressure during combustion was significantly dependent on the intake manifold pressure, and the corresponding crank angle (CA) was almost kept the same for 1000 RPM and 3000 RPM. Heat release rates for hydrogen combustion presented double-peak under high intake manifold pressure scenarios. Combustion durations over 1000 RPM increased with intake manifold pressure; however, they changed slightly for 3000 RPM. Nitrogen oxides (NO_x) emission concentration increased with intake manifold pressure for 3000 RPM and 5000 RPM; however, intake manifold pressure of 0.6 bar presented the highest value for 1000 RPM. Indicated thermal efficiency was higher than 30% for 1000 RPM and 3000 RPM; and the minimum value was approximately 21% over 5000 RPM and 0.4 bar.