HIGH-EGR DILUTION ENABLED BY DUAL MODE, TURBULENT JET IGNITION (DM-TJI) FOR HIGH-EFFICIENCY INTERNAL COMBUSTION ENGINES

To meet the increasingly stringent future fuel economy and CO2 emission reduction targets for light-duty vehicles, fast and reliable solutions with broader market acceptance are required. It is not about predicting which powertrain technology would have market dominance in future, rather what combination of technologies provides a more accessible and sustainable way to meet those targets. Underlined by the current and future high market share of the internal combustion engines in vehicles with either stand alone or hybridized application, it is still of utmost importance (and will continue to be so) that substantial efforts are rendered towards increasing the efficiency and reducing the regulatory emissions from combustion engines used in light duty vehicles. Pre-chamber ignition enhanced by active air/fuel scavenging can serve as a key technology towards enabling several efficiency improvement techniques for combustion engines such as increased compression ratio or high rate of charge dilution. The Dual Mode, Turbulent Jet Ignition (DM-TJI)/ Jetfire® ignition system is a leading pre-chamber combustion technology which not only offers higher thermal efficiency due to its distinct capability to operate with very high level of external EGR dilution (up to ~50%) but at the same time ensures that compatibility with existing cost-effective aftertreatment systems such as three-way-catalyst (TWC) can be maintained. Dual Mode, Turbulent Jet Ignition (DM-TJI) incorporates an auxiliary air supply apart from the auxiliary fuel injection inside the pre-chamber of a divided chamber ignition concept. The supplementary air supply to the pre-chamber enables effective purging and ignitable mixture formation inside the pre-chamber even with very high EGR dilution. The current work focuses on the testing and development of DM-TJI systems on single cylinder engine platforms. The first part of the study presents the experimental investigations carried out with an optical engine equipped with Prototype II DM-TJI system. This optical engine study reported the first published results with 40% external EGR dilution for a pre-chamber jet ignition engine. Both ultra-lean (up to λ ~ 2) and high EGR (up to ~40%) operation were demonstrated and a range of pre-chamber nozzle orifice diameters were tested. The relative timing between the auxiliary air and fuel inside the pre-chamber was found to be critical to maintaining successful operation at 40% EGR diluted condition. The latter part of the dissertation concerns experiments on Prototype III DM-TJI metal engine with ‘Jetfire’ cartridge design. A comparative analysis conducted on the relative effectiveness of excess air (lean) versus EGR dilution strategies indicated that compared to the lean burn operation, EGR dilution provided comparable thermal efficiency benefits with a marked improvement in NOx reduction, especially in a high compression, knock limited situation. This study showcased that high EGR dilution rates comparable to lean burn operation can be maintained with the DM-TJI system to achieve high thermal efficiency while still operating at stoichiometric air-fuel ratio. Finally, different pre-chamber scavenging/fueling strategies (active vs passive) were investigated in order to compare the EGR dilution tolerances between different scavenging strategies under identical pre-chamber design. The results were also compared with the conventional spark ignition (SI) configuration on the same engine. The analysis found that DM-TJI/Jetfire® ignition system becomes more advantageous in terms of thermal efficiency at higher loads and knock limited operation due to its considerably higher external EGR (up to ~50%) dilution tolerance. At 10 bar IMEPg and 1500 rpm with 13.3:1 compression ratio, DM-TJI/Jetfire delivered a maximum of 7 to 9% improvement in thermal efficiency compared to TJI mode of operation whereas the SI system failed to maintain stable operation at the same condition.