Kinetic Modeling Study of the Ignition Process of Homogeneous Charge Compression Ignition Engine Fueled with Three-Component Diesel Surrogate

An improved surrogate diesel fuel composition has been proposed to simulate the autoignition time of diesel fuel under homogeneous charge compression ignition (HCCI) engine conditions. The surrogate fuel is modeled as a blend of n-heptane, toluene, and cyclohexane. Detailed mechanisms consisting of 1140 species and 4590 reactions were constructed by merging well-developed available chemical kinetics substructures for each chemical species. The optimal ratio of the selected diesel surrogate fuel components, n-heptane/toluene/cyclohexane = 8:1:1, was determined using trial-and-error blend methods. Numerically, the modeled heat-release rate obtained from a zero-dimensional single-zone code for the proposed new model was intensively validated against detailed single- and two-component kinetic models together with the referenced experimental engine data. The obtained results show that the new model provides a remarkable agreement with the obtained experimental data and can capture the autoignition angle and the whole combustion process effectively. Sensitivity analysis and flux analysis were further conducted to understand the roles of the different hydrocarbon classes in diesel fuels, and the key elementary reactions involved in ignition inhibition upon the addition of cyclohexane were identified. It is demonstrated that cyclohexane is a highly reactive species and can be used as a tuning knob to control the delay between the two stages of combustion.