A reduced thermokinetic model for the autoignition of fuels with variable octane ratings

Abstract

The autoignition characteristics of the reference fuels i-octane, n-heptane, and their mixtures at temperatures600–1500 K and pressures ranging 0.3–4.2 MPa are studied by means of a reduced kinetic mechanism comprising five species in six reactions altogether. The scheme is readily adaptable to mixtures of the primary reference fuels via input of an octane number between 0 (=n-heptane) and 100 (=i-octane). Emphasis is placed on the dependence of ignition delay on gas temperature, on the evolution of reaction as portrayed in the temperature-time records, and on the multitude of dynamic features, e.g., two-stage (or multistage) ignition and negative temperature coefficient characteristics inherent to alkane combustion. The reduced model was fitted to numerical results derived from quantitative kinetic modelling andvalidated against currently available data from experimental systems. It was originally designed for application in a computational fluid dynamics code based on a transport equation for the joint probability density function (PDF) of the reacting species. Flame propagation and engine “knock” may thus be described by one consistent model.