Calculation of NOx formation using the detail kinetic mechanism

Combustion of complex hydrocarbons occurs by stages:

• the first stage is very fast disintegration of a fuel molecule on radicals and molecules with smaller number of atoms;

• further there is considerably slower process of delayed burning in which particles with one - two atoms of carbon participate.

For simplification of the description of the first stage of combustion for more complex, than methane, hydrocarbons (components of diesel fuel, biofuel, DME) gross-reactions which describe disintegration of the higher hydrocarbons and their derivatives up to simple molecules and radicals are entered.
Initial disintegration kinetic of a fuel molecule is described by 40 reactions with participation of 10 species.
It is supposed, that regardless of initial composition of hydrocarbon at its combustion in the second phase participate the same simple hydrocarbons. There-fore for the description of delayed burning process non-empirical detail kinetic mechanism of combustion of the elementary hydrocarbon – methane is used.
The kinetic scheme of NO formation at combustion of the methane is com-piled on the basis of the kinetic scheme by prof. Basevich V.J.:

CH₄ + O₂ Û   CH₃ + HO₂
CH₃ + O Û  H + H₂CO
. . . . . . . . . . . . . . . . . .
CH + N₂ Û  HCN + N
N + O₂ Û  NO + O.

The given scheme consists of 199 reactions and determines concentration of 33 species: CH₄, C₂H, C₂H₂, C₂H₃, C₂H₃O₂, C₂H₄, C₂H₅, C₂H₆, CH, CH₂, CH₃, CH₃O, CH₂O, CHO, CO, CO₂, H, H₂, H₂O, H₂O₂, HO₂, O, O₂, OH, N₂, N, NO, NO₂, N₂O, HNO, NH, HCN, CN.
The material balance of the species participating in chemical reactions, is described by system of the kinetic equations:
,
where: C_j, C_k ,… C_ζ are mole fraction of the appropriate substances; τ is time; k_i are the constant of chemical reaction rate, determined on Arrhenius equation:
,
where: A is pre-exponential factor, n are an exponent, Å is energy of activation, R is absolute gas constant.
The numerical solution of the differential equations system is carried out by Gear’s method with variable order of accuracy.

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