Experimental data and kinetic modeling of primary reference fuel mixtures

This paper presents computations based on a semidetailed kinetic scheme for reference fuel (n-heptane and 2,2,4-trimethyl-pentane) mixtures. Model results are compared with several experimental data previously appearing in the literature and with data presented here for the first time. New data, obtained in a pressurized flow reactor at 12.5 atm, report the heat release and gas composition of various dilute, stoichiometric mixtures of primary reference, fuels and oxygen under fixed reaction time. New data from rapid compression machine experiments characterize cool flame phenomena in the low temperature range and define total ignition-delay times for stoichiometric mixtures of primary reference fuels and air mixtures at high octane number. The new data confirm that negative temperature coefficient (NTC) and hot ignition characteristics are a nonlinear function of octane number (ON). A previous kinetic model developed and tested for the oxidation of the individual pure reference fuel is shown to reproduce accurately the autoignition and the various oxidation characteristics of reference fuel mixtures in the earlier experiments, as well as in shock tubes and in a motored engine experiment. Moreover, the model is shown to unify the intrinsic information of the different experimental sources and data and provides a skeletal mechanism from which to derive and validate simpler empirical kinetic models for inclusion in engine design codes. Results also suggest that new studies and experiments are required for a deeper understanding of oxidation processes to include the effects of other molecular structure classes, particularly fuel additives (e.g., ethers, alcohols) and aromatics.

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