Investigation of Alternative Ignition System Impact on External EGR Dilution Tolerance in a Turbocharged Homogeneous Direct Injected Spark Ignited Engine 2015-01-9043
Dilution of a stoichiometric spark ignited (SI) charge with exhaust gas recirculation (EGR) has been shown to improve thermal efficiency and fuel consumption through improved combustion phasing and heat transfer losses at the knock limit in conjunction with a reduction of heat transfer losses and pumping losses at throttled conditions. However, combustion stability can be adversely affected by EGR dilution. The degradation in combustion stability can be mitigated by selecting an ignition system that can successfully propagate a self-sustaining flame kernel in the presence of a high concentration of diluent and increase the apparent burn rate. This investigation examines improvements to EGR dilution tolerance and brake specific fuel consumption (BSFC) for multiple alternative ignition systems at various engine operating points while maintaining a stoichiometric air-fuel ratio. The work was performed on a high compression ratio (CR) turbocharged 4-cylinder direct injection (DI) engine with cooled external EGR. Two configurations of an inductive ignition system were evaluated in addition to four alternative ignition technologies with no attempt to optimize the combustion system hardware. The use of alternative ignition technologies in this investigation show the potential to realize improvements in EGR dilution tolerance and fuel consumption compared to current production technology, normalizing for the parasitic power loss of each ignition system. The results show that utilizing advanced ignition technologies can improve BSFC by 2.4% at the conditions tested.