Comparison of Primary Sensitive Reactions on Fuel Reactivity between Detailed and Skeletal Mechanisms of Gasoline Surrogate

Combustion simulation is of great importance for internal combustion engine development. With the advance of fundamental combustion experiments and theoretical computation, detailed combustion mechanisms of gasoline surrogates have been enhanced with introduction of new reactions and updated reaction rate constants recently. However, detailed combustion mechanisms with tens of thousands of reactions are still not practical for engineering use in view of massive computation cost. As a practical alternative, skeletal mechanisms are usually developed to couple with three dimensional engine combustion simulations. As for skeletal mechanisms, rate constants of some important reactions have to be tuned to reproduce the experimental data due to the omission of intermediate reaction steps, thus are different from those applied in detailed mechanisms. However, whether the skeletal mechanism reproduces the combustion reaction process with similar major reactions as the detailed mechanisms is rarely studied. Therefore, the aim of this study is to investigate the different sensitive reactions between the detailed and skeletal mechanisms that affect the fuel reactivity with brute force sensitivity analysis. Results show that the detailed mechanism predicts more strong negative temperature coefficient behavior than the skeletal mechanism. Similar ignition delays were predicted by both mechanisms around 700 K, while the significant difference occurred around 825 K. For the skeletal mechanism, reactions with rate constants altered by one to three orders could change their role of controlling the fuel reactivity as in the detailed mechanism, and also substantially affect the first stage ignition process. Therefore, procedure for reaction rate constant tuning with optimization directions should be proposed in the future for constructing skeletal mechanisms that could reproduce the combustion characteristics of fuels with similar reactivity controlling reactions as in the detailed mechanisms.