Flame propagation limits in H2+air mixtures in the presence of small inhibitor additives

Concentration limits of combustion in rich hydrogen–air mixtures in the presence of inhibitors

“…4,5 Our method is based on a narrow reaction zone model 6 accounting for the termination of active centers (atoms and radicals) by an inhibitor in the pre-flame zone. Such an approach provides a qualitative description of the experimentally observed features associated with hydrogen combustion in the presence of an inhibitor.…”

“…It is a reverse relationship between the combustion rate and the rate of active center termination by an inhibitor that leads to the formation of FPL at a small inhibitor content of the mixture. 4 An approximate analytical method 4 enabled one to formulate a formation mechanism of the upper FPL based on the account of effective heat losses in trimolecular chain-breaking steps. 5 The mechanism was presented for hydrogen oxidation in air and/or oxygen at atmospheric pressure.…”

“…[7][8][9] However, in this case, heat losses arise from the difference between the heat release in the overall reaction (Q/kcal mol -1 ), which would occur without an inhibitor, and heat release of active center (H atom) termination by an inhibitor (or chemical losses) Q 0 (~44 kcal mol -1 ) 10 for complete inhibitor regeneration. The value of b in equation (1) is defined as follows: 4 where l is the thermal conductivity of the gas mixture; q = (Q -Q 0 ) is the total heat loss in the reaction of H atom termination by an inhibitor; Q is the heat release of the H 2 + O 2 reaction; k 5 is the effective reaction rate constant of H atom with the inhibitor molecule; [O 2 ] 0 and [In] 0 are the initial oxygen and inhibitor concentrations, respectively; E is the activation energy of the chain-branching step (H + O 2 ® O + OH); R is the gas constant; T b and u are the adiabatic flame temperature and normal burning velocity in a hydrogen-air mixture in the absence of an inhibitor, respectively; C p is the thermal capacity at constant pressure; r is the density of a gas mixture at the initial temperature.…”

“…4 Experimental data 3,11,12 [Figures 1(a) and 2(a)] have been processed for a number of inhibitors, and the results are shown in Figures 1(b) and 2(b) in the [In] 0,FPL -u 2 T b 2 /[O 2 ] 0,FPL coordinates. In order to construct straight lines for the corresponding inhibitors on the basis of equation (3), we used the following effective values of reaction rate constants for a hydrogen atom and an inhibitor molecule: for CHF 3 , 0.1×10 -11 ; for C 2 F 4 Br 2 , 0.23×10 -11 ; for hexene, 0.47×10 -11 [ Figure 1(b)], for ethanol, 0.93×10 -12 ; for n-butanol, 0.27×10 -11 , for prop-2-en-1-ol, 0.45×10 -11 cm 3 molec -1 s -1 [ Figure 2(b)].…”

Features of initiation of spherical flames in mixtures of natural gas and isobutylene with oxygen in the presence of inert additives

“…In the mechanisms of hydrocarbons oxidation, the reaction of nonlinear branching, which can provide non-thermal flame propagation, is missing. [4][5][6] Therefore, the only feedback factor responsible for the occurrence of a stationary propagating flame is warming-up. Thus, the thermal theory 1 with regard to combustion kinetics 5,6 is applicable to the flame propagation processes.…”