HCCI mode has shown its potential to improve emissions and efficiency in internal combustion engines. In addition, it has open the possibility to use a wider range of fuels than in SI and CI engines. However, the engine running zone is still one of the main challenges that HCCI has to face. We have investigated this zone in the case of ethyl acetate using CFD simulations with a simplified combustion mechanism. This paper describes how ethyl acetate influences the running zone of HCCI engines compared to iso-octane.
Biochemical conversion of fermentable biomass can produce large quantities of esters by the reaction of ethanol with volatile organic acids. Among them, ethyl acetate has a low vaporization temperature and a high auto-ignition temperature. Preliminary experiments on SI engines have shown that it ignites more slowly than gasoline even if their physical properties are similar.
As fuel oxidation kinetics determine start of ignition, heat release rate and part of the emissions in HCCI engines, we used a detailed mechanism for ethyl acetate in a zero-dimensional analysis. Based on these results, we also developed a simplifed combustion mechanism for this molecule in order to simulate HCCI mode using a commercial CFD software (Fluent).
Different engine settings are investigated in an axisymmetric geometry. They are also studied with a simplified mechanism for iso-octane in order to compare the extents of the running zones. Using ethyl acetate, the knock limit is, as expected, expanded to higher loads.