OCR Text |
Show CH + N2 - HCN + N (R4) Under fuel-lean condition, HCN and N produced from R4 are rapidly converted to via the following principal reactions (see Miller and Bowman, 1989 and Glagborg et al., 1992), HCN + O -* NCO + H (R5) NCO + H - NH + CO (R6) NH + H -+ N + H2 (R7) N + OH *+ NO + H (K*) Under fuel-rich condition, the conversion of HCN and N to NO is no longer rapid. Instead the following reactions become dominant (see Miller and Bowman, 1989 and Glagborg etal, 1992): CH + NO - HCN + O (R8) CH2 + NO -+ HCN + OH (R9) N + NO - N2 + O (Rib) CH3 + N - HCN + 2tf (RIO) and cause a decrease in NO and N-atoms. (The reaction C + NO -» CN + O should included as part of the N O destruction mechanism. It is ignored here because the C-atom concentration is assumed to be negligible in the natural gas flames of this study.) Calculation of NO Source It should be noted that the above reactions represent only a fraction of the many overall N O formation mechanism. They were selected based on detailed kinetic studies (such as Miller and Bowman, 1989 and Glagborg et al., 1992 ) to provide only an approximate estimation of N O formation. As noted earlier, the essence of N O modelling is to calculate the source term of NO, SN0, due to the above N O reactions. Based on chemical kinetics, SN0 has the form: 3 |