A Computational Study of the Effect of Fuel Reforming, EGR and Initial Temperature on Lean Ethanol HCCI Combustion 2004-01-0556
Homogeneous charge compression ignition (HCCI) engines have great potential in ultra-low NOx emissions, high efficiency and low particulates. The major disadvantage of HCCI lies in a narrow operating range with low power output. We investigated the expansion of the acceptable operating range (AOR) using fuel reforming complemented by exhaust gas recirculation (EGR), to control the chemical kinetics which dominates HCCI combustion. The study is carried out using a single-zone well-stirred reactor model and established reaction mechanisms. The HCCI engine is fueled with ethanol of equivalence ratio (Ф) of 0.2, 0.4 and 0.5. The (AOR) must meet both the complete combustion and the maximum NOx limit. It is found that reforming enhances combustion and extends the complete combustion limit to lower initial temperatures, but also increases NOx emissions. For Ф's of 0.5 and 0.4, the NOx limit cannot be met without the complementary use of EGR to lower the NOx emission. It is found that reforming is not as effective as EGR in widening the operating range at the Ф's studied. However, reforming may still be useful in HCCI combustion, since hydrogen is reported by others to lower cycle-to-cycle variation .