Evaluation of Pre-Chamber Orifice Orientation in an Ethanol-Fueled Spark-Ignition Engine for Passenger Car Applications

The combination of an alternative alcohol-based fuel and a pre-chamber (PC) combustion process in a spark-ignition (SI) engine allows for both an extension of the lean limit and an increase of the indicated efficiency, while simultaneously achieving low engine-out emissions. The orientation of the PC orifices is crucial for the flow field inside the PC. Orifices with different swirl angles have already been investigated. However, the influence of the orifice offset from the PC center with a fixed swirl angle has not been part of previous research. This study presents investigations of ethanol-fueled combustion systems on a thermodynamic SI single-cylinder engine (SCE) for passenger car applications with a compression ratio (CR) of 16.4. Three active PC layouts with different orifice offsets were investigated. Their combustion behaviors were compared to that of a conventional SI combustion concept. In particular, variations of the relative air/fuel ratio (λ) were performed at both part-load and high-load engine operations. The influence of the different orifice offsets in terms of both the maximum achievable lean limit and the indicated efficiency was found to be small since the combustion behavior was similar for all three PC layouts, and no significant differences in terms of both the lean limit and the indicated efficiency were observed. Compared to the SI configuration, the PC configurations achieved higher maximum indicated efficiencies. At an engine speed of 2000 1/min and an indicated mean effective pressure (IMEP) of 15 bar, a maximum indicated efficiency of 46.5% was achieved with a λ of 1.8. Moreover, a maximum λ of 2.0 was achieved with a PC configuration, while the maximum achievable λ with SI was 1.7. This work provides insights that help to understand the influence of the PC orifice offset on the combustion of an active PC application and shows approaches for future research.