| OCR Text |
Show 1.6.10 relatively small dependence on A of the reduction in NO at low temperatures (cf. Fig. 3 and Sec. III). 4. The rate at which H-atoms are destroyed by reactions other than (3a) was represented by -CH]/TH, where TJJ is a characteristic time for the destruction process. The corresponding term [H]eq/Tjj representing the reverse reaction was left out, because it is small whenever the H-atoms play a role of importance (i.e., when [H] »[H]eq). As was the case in the model considered in the previous two sections, reactions of NH2 with 0 and 02 are neglected with respect to that of N H 2 with OH (reaction 2). The basis for this neglect is the smallness of the corresponding reaction rates, as estimated from available rate constants together with relative equilibrium concentrations in typical post-flame gases generated by fuel-lean combustion. The revised model leads to the following equations: d[NH2] dt • k4[NH3][H] + k3[NH3][0H] - k j N H j H N O ] - k2[NHj[0H] d[0H] [OH]..- [OH] •^ + kjaCNHjHOH] - k2[NH2][0H] - k3[NH3][0H] dt T0H d[H] - [H] - = + kl0c[NH2][0H] - k4[NH3][H] dt TH Making use of the quasi-steady state approximation by setting each of these expressions equal to zero yields d[NH3] kjk3 l + rHk4[NH3] - ^ T ~ = " - £ N H 3 ] [ N 0 ] c " (i -oc)[NO] + [NO]r (21) 2 I + TUMNH,] r -, r -, C H 4L 3J [N0] + [ N 0]c ci[N0] _ [NO] - [N0]c d[NH3] (22) dt [NO] + [N0Jc dt where [NO]c is given by P , 2 a3 1/2 rl -b/2 , 1 [N0]_ = - ( > cosl-arc cos ? TTo J - P c 3 2? 3 <-a3/27)1 / 2 3 a = a - p2/3, b = <2p3 - 9pq • 2?r>/27, |
