Effect of EGR Chemical Components and Intake Temperature on HCCI Combustion Development

In an optical Homogeneous Charge Compression Ignition (HCCI) engine, experiments were performed to study the combustion of different surrogate fuels (n-heptane, 75%n-heptane/25%isooctane, 80%n-heptane/20%toluene). The effect of laboratory simulated EGR rates, inlet temperatures and the presence of different chemical species in the EGR on the ignition combustion timings were analyzed at a fixed equivalence ratio (0.3). The mixture homogeneity was verified by Laser-Induced-Fluorescence on the toluene. The experimental results affirm that the EGR delays the combustion unlike the inlet temperature. Intake CO and CH₄ addition has no effect on ignition timings whereas a promoting effect of NO is checked. A zero-dimensional model was developed and offered encouraging tendencies by comparison with the experiments.