Effect of pre-chamber scavenging strategy on EGR tolerance and thermal efficiency of pre-chamber turbulent jet ignition systems

Dual Mode, Turbulent Jet Ignition (DM-TJI) is an engine combustion technology that incorporates an auxiliary air supply apart from the auxiliary fuel injection inside the pre-chamber of a divided chamber ignition concept. Compared to other active (auxiliary fueled) and passive pre-chamber ignition technologies, the DM-TJI system has the distinct capability to operate with very high level (up to similar to 50%) of recirculated exhaust gas (EGR). Thus, unlike typical lean (excess air dilution) operated pre-chamber ignition technologies, the DM-TJI system enables the use of widely utilized low cost three-way-catalyst (TWC) while still running at high level of dilution (with EGR). The supplementary air supply to the pre-chamber enables effective purging and ignitable mixture formation inside the pre-chamber even with very high external EGR rate. The current work presents the results of experimental investigation conducted on a Prototype III Dual Mode, Turbulent Jet Ignition (DM-TJI) (or Jetfire ignition) single cylinder metal engine. Different pre-chamber scavenging/fueling strategies (active vs passive) were investigated in order to compare the EGR dilution tolerances between different scavenging configurations under identical pre-chamber design parameters (pre-chamber volume and nozzle configuration). Tests were conducted at two regularly encountered operating conditions (6 and 10 bar IMEPg at 1500 rpm) in typical drive cycles. Results are also compared with the conventional SI (spark ignition) configuration on the same engine. The results indicate that to maintain very high EGR diluted (up to similar to 50%) operation the auxiliary air supply to the pre-chamber is of paramount importance. The analysis found that DM-TJI/Jetfire ignition system is more effective in terms of thermal efficiency at high load knock limited situation due to its considerably higher external EGR dilution tolerance. Higher EGR rate offered better combustion phasing and improved thermal efficiency considerably. It was found that with the elevated 13.3:1 compression ratio and 10 bar load, SI could not maintain knock free stable operation and DM-TJI/Jetfire delivered 7%-9% improvement in thermal efficiency compared to TJI mode of operation with no air delivery to the pre-chamber.