Hydrocarbon Oxidation at High Temperatures

Abstract

Abstract The detailed knowledge of combustion mechanisms is important, for example for the control of (kinetically determined) pollutant formation (e.g. NO, hydrocarbons, soot), for ignition problems, or for the extrapolation to technologically important but experimentally inaccessible condition. – In this review it is described how by suitable separation and elimination of unimportant reactions a mechanism is developed with the aid of the present kinetic data for the elementary reactions involved. This mechanism explains, without fitting, the currently available experimental results for laminar premixed flames of alkanes, alkenes and acetylene (flame velocity and structure of free flames, concentration and temperature profiles in burner‐stabilized flames). These experimental results are simulated by the solution of the corresponding conservation equations with suitable models describing diffusion and heat conduction in the multicomponent mixture considered. – In lean and moderately rich flames the hydrocarbon is attacked by O, H, and OH in the first step. These radicals are produced by the chain‐branching steps of the oxyhydrogen reaction. The alkyl radicals formed in this way always decompose to smaller alkyl radicals by fast thermal elimination of alkenes. Only the relatively slow thermal decomposition of the smallest alkyl radicals (CH 3 and C 2 H 5 ) competes with recombination and with oxidation reactions by O atoms and O 2 . This part of the mechanism is rate‐controlling in the combustion of alkanes and alkenes, and is therefore the reason for the similarity of all alkane and alkene flames. – In rich flames of aliphatic fuels, acetylene becomes a very important intermediate leading to soot precursors and to Non‐Zeldovich‐NO. Details of the reaction mechanisms are not yet known.