Potential of EGR and intake heating for load extension using gasoline-ethanol blends as low reactivity fuel in an intelligent charge compression ignition engine

Abstract

Uncontrollable ignition at high load and local misfire at low load limited the reasonable operation range of low-temperature combustion. The dual-fuel intelligent charge compression ignition (ICCI) combustion utilized two direct injectors organizing the flexible stratification through various injection strategies. Exhaust gas recirculation (EGR) delays the combustion phasing to keep the ignition under control, whereas the oxidation of incomplete products and the heat release at the late stage of combustion deteriorate. Intake heating provides the heat necessary to stabilize the ignition process at low load despite complicating the intake manifold. In this work, the load extension potential of different gasoline-ethanol blends as low reactivity fuel (LRF) was investigated, while the EGR dependence at high load and intake heating influence at low load were compared in ICCI mode. The misfire problem for 50% ethanol (E50) and 85% ethanol (E85) was solved at about 40 °C intake air temperature compared with 10% ethanol (E10). When the intake air temperature was about 60 °C, the combustion efficiency for pure ethanol (E100) reached the same level, compared with others. For the high load range, E10 faced uncontrollable ignition by the single diesel injection even with an ultra-high EGR rate, leading to the adoption of a two-stage diesel injection strategy. For E100 and E85, the ignition was highly associated with the single diesel injection even in the absence of EGR. Although E50 and E85 reached over 52% thermal efficiency under different EGR rates, E50 hardly illustrated the clean combustion features like pure ethanol and E85.