Numerical study on the improvement of combustion behavior using passive turbulent jet ignition in a small turbocharged port fuel injection engine fueled with ammonia

The combustion characteristics and performance of a small internal combustion engine fueled exclusively with liquid ammonia using a passive turbulent jet ignition system were investigated numerically. Ammonia under conventional spark ignition shows long ignition delay, slow flame propagation, and unstable operation because of its low reactivity and high ignition energy demand. The passive turbulent jet ignition system introduces a pre-chamber of 5.2% clearance volume with six orifices of 1.5 mm, discharging high-velocity jet flames into the main chamber. These jets generate strong turbulence, initiate multiple ignition kernels, and accelerate flame propagation. A one-dimensional model provided system-level conditions for three-dimensional simulations. At 1600 rpm, the optimal ignition timing occurred at −10° after top dead center (aTDC), producing 148.8 Nm torque, 35.3% brake thermal efficiency, and 582.5 g/kWh brake specific fuel consumption. At 3000 rpm, the optimal spark timing advanced to −20° aTDC, yielding 142.5 Nm torque, 36.2% brake thermal efficiency, and 568.1 g/kWh fuel consumption. Across operating conditions, the passive turbulent jet ignition system reduced combustion duration, improved efficiency, and promoted uniform premixed flame formation. Numerical simulations demonstrate that passive turbulent jet ignition significantly enhances ammonia combustion stability and efficiency, even under high-speed operation. These results suggest the technology could serve as a practical retrofit solution for small internal combustion engines to address combustion efficiency challenges in advancing carbon-neutral mobility.