Experimental investigation on the combustion characteristics of ultra-lean premixed hydrogen/air using turbulent jet ignition

Amid growing environmental concerns, hydrogen (H₂) is emerging as a prospective alternative fuel for driving internal combustion engines. Employing lean combustion technology in tandem with turbulent jet ignition (TJI) has the potential to enhance combustion rates while mitigating NO_x emissions. Therefore, an experiment was developed to investigate the combustion characteristics of ultra-lean premixed H₂/air by TJI. An active pre-chamber (PC) with an additional H₂ supply was selected. Moreover, the effect of nozzle structures and equivalence ratio was discussed. The results show that with a nozzle diameter of 3 mm and an elevation of Φ_PC to 1.4, the lean flammability limit is extended to an equivalence ratio of 0.13, with a consistently stabilized ignition delay within 4 ms. Increasing the nozzle number also extends the lean flammability limit, but it incurs higher energy losses. Additionally, two ignition mechanisms exist in TJI: flame ignition and combined ignition. The transition from flame ignition to combined ignition commonly occurs when the equivalence ratio of the main chamber drops below 0.3. This transition typically results in higher peak pressures and burnt fuel ratio, lower combustion duration, and longer ignition delay.