Liu, H., Wang, Z., Long, Y., Xiang, S. et al., "An Experimental Study Using Spark-Assisted Stratified Compression Ignition (SSCI) Hybrid Combustion Mode for Engine Particle Number (PN) Reduction in a High Compression Ratio Gasoline Engine," SAE Technical Paper 2016-01-0758, 2016, doi:10.4271/2016-01-0758.
Particle Number (PN) have already been a big issue for developing high efficiency internal combustion engines (ICEs). In this study, controlled spark-assisted stratified compression ignition (SSCI) with moderate end-gas auto-ignition was used for reducing PN in a high compression ratio gasoline direct injection (GDI) engine. Under wide open throttle (WOT) and Maximum Brake Torque timing (MBT) condition, high external cooled exhaust gas recirculation (EGR) was filled in the cylinder, while two-stage direct injection was used to form desired stoichiometric but stratified mixture. SSCI combustion mode exhibits two-stage heat release, where the first stage is associated with flame propagation induced by spark ignition and the second stage is the result of moderate end-gas auto-ignition without pressure oscillation at the middle or late stage of the combustion process. The experimental results show that SSCI is a potential combustion strategy to reduce PN while improving fuel economy of high compression ratio gasoline engine. Under 1600 rpm/WOT condition, the PN of SSCI combustion mode can reach 4*105 1/ml, a 97% reduction compared to the normal GDI spark ignition baseline of 152*105 1/ml.