Abstract:  Jet ignition is an efficient way to achieve lean burn and improve thermal efficiency of the engine. Gas-jet ignition (GJI) combustion was studied with the designed jet igniter， and the characteristics of combustion and emission under passive jet ignition and active jet ignition strategies were investigated. The results show that active ignition extends the excess air ratio to 2 and thermal efficiency is improved 1.5% compared with passive ignition, and based on the active jet ignition, thermal efficiency is further improved to 44.5% when exhaust gas recirculation (EGR) is introduced. The NOx emission at the most efficient point decreases 66% with active jet ignition, whereas the combustion efficiency decreases 3% due to the increase of THC and CO emission. NOx emission further decreases 79% and combustion efficiency keeps stable at 96% with the introduction of EGR.

Key words: natural gas engine , gas-jet Ignition (GJI) ,  lean burn ,  exhaust gas recirculation (EGR)