Chemical dynamics of the autoignition of near-stoichiometric and rich methanol/air mixtures

The homogeneous, isochoric and adiabatic autoignition of rich methanol mixtures is analysed using algorithmic tools of Computational Singular Perturbation. It is shown that ignition delay decreases as the equivalence ratio ϕ increases, due to the faster production of OH radicals via the reactions CH (Formula presented.) OH + HO (Formula presented.) (Formula presented.) CH (Formula presented.) OH + H (Formula presented.) O (Formula presented.) and H (Formula presented.) O (Formula presented.) (+M) (Formula presented.) OH + OH (+M). After ignition and for sufficiently rich mixtures the phenomenon of super-adiabatic temperature (SAT) is observed; i.e. the temperature after ignition decreases with time. This feature is accompanied by the appearance of an explosive mode. With increasing values of ϕ, SAT becomes more pronounced and the explosive mode becomes faster; i.e. its time scale is shortened. SAT is due to the fact that as ϕ increases the role of hydrogen chemistry diminishes and the explosive character of the process is basically generated by endothermic dissociation reactions of carbon-containing species that cause an increase in number of molecules and a temperature decrease.