Numerical study of a butanol/heptane fuelled Homogeneous Charge Compression Ignition (HCCI) engine utilizing negative valve overlap

The calibration and comparison to experimental data of a parallel computing multi-zone combustion model for simulating operational characteristics of an n-butanol/n-heptane fuelled Homogeneous Charge Compression Ignition (HCCI) engine utilizing the negative valve overlap (NVO) technology is described. The model is calibrated using one experimentally characterized operating point and by taking into account the major features of NVO. The model simulations at other four operating points closely match the cylinder pressure trace and heat release rates of the experiments. The unburned hydrocarbon emission is predicted to a reasonable level while NOx (nitric oxide NO and nitrogen dioxide NO2) formation is under-predicted. The difficulty in mapping the NOx emission is attributed to the fact that the combustion model operates within the closed cycle period of engines and therefore does not capture the complexity of the charge stratification within the NVO equipped engine. Nevertheless, the trend of increasing NOx levels with the increasing fraction of butanol in the fuel mixture is captured and the model is able to predict the pressure, heat release rates, and combustion phasing for the three fuel blends tested.