Effect of Passive Prechamber and Direct Water Injection on Performance and Efficiency Improvement within a Gasoline Engine

With the increasingly stringent global energy-saving policies, gasoline engines are facing great challenges, and how to achieve high efficiency in gasoline engines has become an urgent technical challenge. Passive prechamber technology can partially enhance the thermal efficiency of high-load, high-compression-ratio engines under lean-burn conditions, but its effectiveness in reducing NOx emissions is limited. In contrast, the introduction of direct water injection (DWI) technology can further optimize thermal efficiency under lean-burn conditions while significantly lowering NOx emissions. Through three-dimensional flow simulation analysis coupled with detailed chemical reaction mechanism, the engine combustion characteristics under stoichiometric conditions and lean-burn conditions are systematically investigated in this paper by the effect of passive prechamber jet ignition combined with direct water injection. It is shown by the results that CA50 can be effectively advanced, degree of constant-volume combustion can be improved, and efficiency improvement can be realized by this technical solution. Under stoichiometric conditions, optimization of the spark timing increased the indicated thermal efficiency from the baseline value of 34.69% to 39.75%; however, the NOx emissions under this condition increased by 26.01% compared with the baseline. At λ = 1.4, optimization of the spark timing increased the indicated thermal efficiency from the baseline value of 34.69% to 44.82%, while the NOx emissions were reduced by 67.28% relative to the baseline. Compared with stoichiometric operation, the combination of a passive PC and DWI under lean-burn conditions substantially reduces the knock tendency, enabling higher thermal efficiency together with lower emissions.