Federal Republic of Germany AND

A kinetic mechanism of 1011 elementary reactions with 171 chemical species for n-heptane ignition is analysed and reduced to 4 global steps with adjusted rate coefficients to describe ignition at pressures around 40 atm. Two of these steps account for the high temperature branch and the other two for the low temperature branch of the ignition mechanism. The ignition delay time passes through a negative temperature dependence during the transition between the two branches. This is accounted for by the reversible third reaction step, which models the first and second 02-addition in the degenerated chain branching mechanism at low temperatures. Ignition delay times calculated with the adjusted 4-step model are com-pared to those from the detailed kinetics and experimental data. Finally the 4-step mecha-nism is analysed by asymptotic methods and explicit ignition delay time formulas are derived. Introductíon Auto-ignition plays a central part in many prac-tical combustión systems burning hydrocarbon fuels. One example is the ignition of the fuel spray in a Diesel engine, another is the auto-ignition of th