Predicting performance of a methane-fueled HCCI engine with hydrogen addition considering knock resistance

The performance and knock-resistance characteristics of a homogeneous charge compression ignition (HCCI) engine fueled by methane and blends with hydrogen were investigated numerically using a one-dimensional cycle simulation. Parameters that affect combustion, such as intake temperature, intake pressure, excess air ratio (EAR), and mass fraction of hydrogen additive were selected as independent variables. The engine model was based on a Hyundai D6BT engine and the HCCI operation range was determined before the simulation. Modeling was performed based on the ranges found: intake temperatures of 443-493 K, intake pressures of 130-160 kPa, and EARs of 2.0-2.6. Within the operational ranges, the mass fraction of hydrogen added to the fuel was varied from 0 to 3%. The model was validated and calibrated by several sets of experimental data, under conditions of 0% and 1% hydrogen addition for various intake temperatures, pressures, and EARs. The results show that added hydrogen improved knock resistance under given conditions, and also slightly improved torque output, engine efficiency, and emissions. The peak of in-cylinder pressure decreased and was retarded, with slower combustion and heat release rates. That is, a wider operation range with a decreased risk of heavy knocking and enhanced ignition capabilities was achieved with hydrogen addition.