The internal combustion engine (ICE) is projected to remain the dominant technology in the transport sector over the short to medium term, and there exists significant potential for further improvements in fuel economy and emission reductions. One promising approach to enhancing the efficiency of spark ignition engines is the implementation of passive pre-chamber spark plugs.
The primary advantages of pre-chamber-initiated combustion include the mitigation of knocking, an increase in in-cylinder turbulence, and a combustion process that is both faster and more stable compared to that achieved with conventional J-gap spark plugs. Additionally, the higher ignition energy provided by pre-chamber spark plugs enables operation under higher intake pressures, maintains similar exhaust gas recirculation rates, and supports leaner combustion conditions. These benefits are predominantly attributed to volumetric ignition via hot, reactive jets. However, the pre-chamber spark plug also presents several challenges. Its drawbacks include suboptimal cold-start behavior, difficulties in catalyst heating when accompanied by aggressive spark retard, and inferior low-load performance resulting from reduced charge motion, elevated residual gas concentrations within the pre-chamber, and increased wall heat transfer at low loads. Furthermore, the challenge of adequately heating the catalytic converter persists due to delayed ignition timing.
In this study, various passive pre-chamber configurations were systematically investigated and evaluated based on key performance metrics. Engine operation was categorized into three specific regimes: catalyst heating on a cold engine (operated at 1200 rpm with an IMEP of 3 bar), the optimal efficiency point corresponding to a minimum brake specific fuel consumption (operated at 2000 rpm with an IMEP of 14 bar), and a high-speed load sweep conducted at 4000 rpm. The experimental campaign was executed in two phases, allowing for iterative design modifications informed by the findings of the initial phase. Ultimately, the optimized pre-chamber design successfully achieved a minimal specific exhaust heat flux (SEHF), maintained the desired combustion stability, and extended the high-load operating envelope up to an IMEP of 18.5 bar.