Reduced reaction schemes for methane, methanol and propane flames

Recently proposed elementary reaction schemes are systematically reduced to the smallest number of steps that is algebraically tractable and still provides a realistic flame structure. The reduction uses steady state assumptions for all intermediates other than H 2 , CO and the H-radical. Furthermore, the steady state relations for O and OH are simplified by reatining only the largest terms. For the example of methane there results a quasi-global four-step mechanism, valid for flame calculations ( I ) C H 4 + 2 H + H 2 O = C O + 4 H 2 ( I I ) C O + H 2 O = C O 2 + H 2 ( I I I ) 2 H + M = H 2 + M ( I V ) O 2 + 3 H 2 = 2 H + 2 H 2 O The rates of these reactions are explicit expressions in terms of the concentrations of the seven reactive species in the system. They contain kinetic data exclusively from the original elementary reaction scheme that includes the C 1 - and the C 2 - chain. Similarly, for methanol flames we obtain a four-step mechanism where the first reaction is replaced by ( I ) C H 3 O H + 2 H = C O + 3 H 2 − . For propane the fuel consumption occurs through the two parallel steps ( I a ) C 3 H 8 + 2 H + 2 H 2 O + O 2 = 2 C O + 7 H 2 + C O 2 ( I b ) C 3 H 8 + 4 H + 3 H 2 O = 3 C O + 9 H 2 These represent the two parallel oxidation channels a ) via the n − propyl radical n − C 3 H 7 which procedes via C 2 H 4 to C H 2 and b ) via the iso − propyl radical i − C 3 H 7 which procedes via C 3 H 6 to C H 3 . Numerical calculations using Warnatz' program have been performed for the reduced schemes. The agreement with calculations using large reaction schemes for high temperature hydrocarbon flames is very good for lean and rich flames as far as the flame structure and flame velocities are concerned.