AbstractPrechamber jet ignition can significantly enhance the progress of combustion and improve fuel consumption. Based on a single-cylinder gasoline engine and a small-volume prechamber, the prechamber local air-fuel equivalence ratio, ignition type, and compression ratio were examined under lean burn conditions. The results show that spray wetting the wall of the prechamber is inevitable. As the quality of the fuel injection increases in the prechamber, the quality of the spray wetting the wall also increases, and the particle number (PN) emissions increase significantly. A rich mixture in the prechamber can improve ignition and enhance the main chamber combustion process. However, an air-fuel equivalence ratio near 1 in the prechamber has a greater fuel saving potential and lower PN emissions. When the excess air coefficient in the main chamber is below 1.4, the gross indicated thermal efficiency (GITE) of the prechamber is lower than that of the spark plug ignition. When the excess air coefficient in the main chamber is above 1.4, the prechamber significantly improves the thermal efficiency of the lean burn. The prechamber achieves a maximum GITE of 48.5% when the excess air coefficient in the main chamber is 1.8. Moreover, a prechamber combined with a high compression ratio can further improve combustion and reduce fuel consumption in the lean burn engine. Prechamber ignition extends the lean burn limit to the excess air coefficient value of 2.1 in main chamber, and nitrogen oxides emissions are as low as 58 ppm. Furthermore, the higher the compression ratio, the more the mixture gas is pushed into the prechamber, which increases the prechamber ignition energy and enhances the combustion process of the main chamber.