Abstract
Opposed rotary piston engines are characterized by high power density, which makes them as an ideal power source for hybrid vehicles and range extended electric vehicles. Hydrogen applications can fully exhibit the merits of opposed rotary piston engines, and achieve zero carbon dioxide emissions; however, the applications seriously worsen the nitrogen oxides emissions. In this investigation, lean-burn was adopted to achieve low nitrogen oxides emissions using a three dimensional numerical simulation approach. The results indicated that engine speed of 3000 r/min presented the highest in-cylinder pressure during combustion among the given scenarios, and the pressure over 3000 r/min depended more on the equivalence ratio than that of 1000 r/min and 2000 r/min. Heat release rates were very sensitive to low equivalence ratio. Combustion duration over the equivalence ratio of 0.8 was the shortest among 1000 r/min cases; however, it decreased with equivalence ratio for 2000 r/min and 3000 r/min. Heat loss rates through cylinder walls increased significantly with engine speed, meanwhile they were more dependent on the equivalence ratio over higher engine speed. Maximum nitrogen monoxide formation rates over 3000 r/min occurred slightly earlier than those of 1000 r/min and 2000 r/min. Equivalence ratio of 0.8 showed the highest indicated thermal efficiency over corresponding engine speed, and nitrogen dioxide emission factors were quite low over the equivalence ratio of 0.7 for the given engine speed.
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•Start of hydrogen combustion was retarded with the increase of equivalence ratio.•3000 RPM presented the highest in-cylinder temperature and combustion efficiency.•Indicated thermal efficiency had the highest value over the equivalence ratio of 0.8.•Heat loss through cylinder walls depended on the engine speed and equivalence ratio.•NO emission factor was much low over the equivalence ratio of 0.7.