Investigation on the potential of using carbon-free ammonia and hydrogen in small-scaled Wankel rotary engines

As a zero-carbon fuel and hydrogen carrier, ammonia has received much attention for its excellent carbon reduction potential. To explore the feasibility of zero-carbon ammonia as fuel for in small-scaled Wankel rotary engines, a computational fluid dynamics model coupled with a kinetic mechanism was established and validated. It is found that the fuel mixture cannot be ignited when the hydrogen substitution ratio (HSR) is less than 5%. Increasing HSR shortens flame development period and intensifies combustion. When HSR is greater than 12.5%, the fuel can be burned up, and the position of peak heat release rate remains close to 20°EA aTDC. Elevated HSR leads to higher NO emissions but lower NO2 and N2O emissions. As expected, advancing ignition timing (IT) significantly enhances combustion efficiency and reduces emissions. Advancing the IT results in a slight increase in the unburned area at the rear of combustion chamber, coupled with a rapid decrease in the unburned area at the front, collectively reducing unburned fuel. When IT is advanced from −5 to −35°EA aTDC, emissions and performance increase rapidly, whereas when advanced to −45°EA aTDC, both are nearly unchanged and combustion efficiency decreases.