Enhanced after-treatment warm up in diesel vehicles through modulating fuel injection and exhaust valve closure timing

Abstract

Exhaust after-treatment (EAT) units in diesel engine systems necessitate high exhaust temperature (above 250oC) to perform effectively and reduce the emission rates sufficiently during operation. Several methods such as exhaust throttling, early exhaust valve opening and late post fuel injection require high fuel penalty (mostly above % 10) to sustain EAT systems above 250oC. The aim of this numerical work is to combine delayed fuel injection and advanced exhaust valve closure in a diesel engine model to reduce the fuel penalty below % 10 as exhaust temperature is improved over 250oC. Fuel injection timing (FIT) is delayed up to 13oCA degrees from the nominal position. Exhaust valve closure is simultaneously advanced up to 30oCA degrees from the baseline as fuel injection is delayed in the system. Numerical results demonstrated that retarded fuel injection improved exhaust temperature moderately and needed relatively high fuel penalty. Unlike FIT modulation, early exhaust valve closure (EEVC) enhanced engine-out temperature effectively and required lower fuel penalty. However, EEVC caused a significant exhaust flow reduction, affecting EAT warm up negatively. Simultaneous application of EEVC and delayed FIT decreased the exhaust flow rate less than that in EEVC alone mode. Moreover, it kept fuel penalty below % 10, which was not found possible with RFI method alone in the system. EEVC + RFI combined method was also seen to heat up the EAT unit above 250oC in a fuel saving manner compared to RFI alone mode.