Extending ultra-lean burn performance of high compression ratio pre-chamber jet ignition engines based on injection strategy and optimized structure

Abstract

The pre-chamber jet ignition technology significantly enhances the thermal efficiency and lean burn limit of the engine. In this study, a single-cylinder pre-chamber engine is subjected to a performance limit test. Through optimization of the pre-chamber fuel injection strategy, enhancement of the pre-chamber nozzle structure, and implementation of adiabatic piston technology, the gross indicated thermal efficiency of the spark ignition gasoline engine has successfully exceeded 51%, and the lean burn limit has been extended to lambda values greater than 3.1. For the selection of pre-chamber injection parameters, high injection pressure, minimal enrichment, and injection timing in the middle of the compression stroke are found to achieve both high fuel economy and lean burn performance. Moreover, the orientation of the pre-chamber nozzle has a significant impact on the lean burn performance of the engine, with the nozzle aiming at the top of the piston and avoiding pointing towards the cylinder wall. Under the conditions of high compression ratio and ultra-lean burn, the jet ignition followed by end-mixture gas auto-ignition results in a double-peak heat release process. Additionally, adiabatic piston technology shows potential in expanding the lean burn limit of engines while simultaneously mitigating HC emissions and engine heat transfer losses.