Development of Isooctane Skeletal Mechanisms for Fast and Accurate Predictions of SOC and Emissions of HCCI Engines based on LLNL Detailed Mechanism

Fast and accurate numerical analysis is not only important for studying Homogeneous Charge Compression Ignition (HCCI) technology but also critical for designing HCCI engines. Chemistry plays the major role in determining Start of Combustion (SOC) and emissions of HCCI engines. The Lawrence Livermore National Laboratory (LLNL) detailed isooctane mechanism contains 857 species and 3,606 reaction steps making the calculation too expensive. This work describes a recent development of isooctane skeletal mechanisms for speeding up numerical simulations of HCCI. By using the rate analysis, two skeletal mechanisms were constructed: one with 258 species and the other with 291 species. The former was developed for accurate predictions of SOC and the latter is an expanded version of the one with 258 species aiming at accurate predictions of both SOC and emissions. Validations of the performances of these two skeletal mechanisms were conducted extensively for the operation regimes anticipated by HCCI engine applications. Both skeletal mechanisms are found satisfactory in predicting SOC with a speeding up factor of 15-20. The expanded version is found necessary for accurate predictions of CO and unburned hydrocarbon emissions