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.