Prediction of Preignition Reactivity for n-Butane and iso-Butane Blends Using a Reduced Chemical Kinetic Model

Recently, we reported the development of a new reduced chemical kinetic model for predicting reactivity and autoignition behavior of primary reference fuels in a motored research engine. The predicted oxidation behavior (ignition delay, preignition heat release, and evolution of key chemical species) is in fairly good agreement with experiments. In addition, the model reproduced the experimentally observed dependence of overall reactivity on charge density and manifold inlet conditions. This paper reports our initial effort to apply this new reduced chemical kinetic model to other fuels. Specifically, the model was tested using neat n-butane and n-butane/iso-butane blends (10, 20, and 48 percent by volume iso-butane) under skip fired conditions. The only adjustments made in the model were to the fuel specific rate parameters of the RO2· isomerization reaction, the reaction of aldehydes with OH·, and the reaction forming cyclic ethers. The ignition delay, heat release, fuel consumption and CO formation in the end gas were calculated using this model and were compared with predictions using the Hu and Keck reduced chemical kinetic model. Results showed that with adjustment of fuel specific rate parameters our model can predict the magnitude of cumulative heat release quite well with a 20 CAD discrepancy in the timing. The model can also generally predict the fuel consumption and CO formation, with the characteristic shapes of the profiles varying as the percentage of iso-butane increases in the blend. This demonstrates that the model has the potential to be applicable for a broader range of fuels.