Numerical study on the load-range extension of gasoline-fueled homogeneous charge compression ignition combustion in a light-duty diesel engine

Abstract

Recent research on homogeneous charge compression ignition (HCCI) engines has demonstrated that these engines can complement traditional compression-ignition engines. The higher octane number and vapor pressure make gasoline-like fuels more suitable for port fuel-injected HCCI engines. Doping gasoline with ignition promoters eliminates intake charge preheating or turbocharging requirements and reduces cyclic variations in combustion, especially at lower engine loads. Seeding the intake charge with suitable diluents enables higher load extension of doped gasoline-fueled HCCI engines by preventing knocking. In the present study, HCCI experiments in a 0.662-litre, light-duty diesel engine using 2-Ethylhexyl nitrate (EHN)/gasoline blends formed a database for validating computational fluid dynamic (CFD) simulations. The CFD tool could capture the qualitative trends of HCCI combustion, performance, and emission parameters. The validated CFD tool was then used to investigate a suitable ignition promoter other than EHN to blend with gasoline such that a constant combustion phasing was achieved. Di-tert butyl peroxide (DTBP), hydrogen peroxide, nitric oxide, nitrogen dioxide (NO2), and ozone were the investigated ignition promoters. Further, the effects of adding diluents, including exhaust gas recirculation, nitrogen, carbon dioxide (CO2), and water vapor (H2O) on EHN-gasoline HCCI combustion, were studied for a constant combustion phasing retardation of 5 °CA towards aTDC. The primary objective of the present study was to select the most suitable ignition promoter and diluent for gasoline-fueled HCCI combustion. The results show that the least quantity of EHN and CO2 was required to control HCCI combustion phasing among the tested ignition promoters and diluents. Using NO2 as an ignition promoter and H2O vapor as a diluent improved the gross indicated thermal efficiency by 24% and 17%, respectively, compared to DTBP and EGR, which produced the lowest gross indicated thermal efficiency.