Modeling and Experimental Validation of Prechamber Jet Penetration Considering Jet Density and Ejection Pressure Variations

Abstract

Although prechamber (PC) is regarded as a promising solution to enhance ignition in lean-burn gas engines, a lack of comprehensive understanding of PC jet penetration dynamics remains. This study proposed a zero-dimensional (0D) model for PC jet penetration, considering the mixing of combustion products and unburned gases in jets and the floating ejection pressure. A combustion completion degree was defined by employing fuel properties and heat release to estimate the time-varying jet density. Pressure differences between the PC and the main chamber (MC) were referred to as the ejection pressure. Then, this model was validated against experimental data from a constant volume chamber (CVC) and a rapid compression and expansion machine (RCEM) with CH4-H2 blends at different equivalent ratios. Results showed that the proposed model can provide a good prediction in stationary and turbulent fields with the calibrated model coefficient. The overall jet penetration exhibits a t0.5 dependence due to its single-phase characteristic and the relatively lower density compared to the ambient gas in MC. The flame propagation speed and heat release in PC influence the combustion completion degree at the start of jet ejection. The mass fraction of burned gas in the ejected jet grows in response to the mixture equivalent ratio. Jet penetration is primarily driven by ejection pressure, with tip dynamics barely affected by the pressure difference after peaks. Tip penetration intensity rises with increasing fuel equivalent ratio and H2 addition, owing to the faster flame propagation. These findings can offer useful suggestions for model-based design and combustion model development for gas engines.