Rate coefficients of elementary processes in the hydrogen—nitrogen oxide systems

5 RATE COEFFICIENTS OF ELEMENTARY PROCESSES IN THE HYDROGEN-NITROGEN OXIDE SYSTEMS 

Data on the elementary steps in the H—N—O system is much less plentiful than in the case of the hydrogen—oxygen system, and for many reactions there is no reliable measurement available. Table 49 summarizes the data which are available. 

When small quantities of hydrocarbons and related compounds are added to hydrogen—oxygen mixtures at around 500 °C, one or more of three effects may be observed. 

there is an inhibiting effect of the additive on the low pressure explosions, so that the second limit pressure is reduced and the first limit is raised on addition of the hydrocarbon [329—331]. Secondly, there may be an increase in the maximum rate (of decrease of pressure) in the slow reaction [330]. Thirdly, induced explosions may occur in some cases (not with methane) at pressures outside the + O2 explosion peninsula. In most cases such induced explosions appear as one sharp explosive reaction. However, they are sometimes characterized (e.g. with CaHg at 560 °C) by an induction period during which there is a rapid pressure increase, and this is followed immediately by a very rapid pressure decrease in the system. It is probable that all the induced explosions follow this two-stage pattern. This type of explosion does not occur in H2—Oj—CH4 mixtures because methane is not as reactive as propane in 

Of greater interest here are the inhibition phenomena at the first and second explosion limits, and certain other experiments in which traces of hydrocarbons are added to slowly reacting H2 + N2 + O2 mixtures at around 773 K in aged boric acid coated vessels. Both types of measurement open up the possibility of examining the reactions of the radicals of the H2 + O2 system with the additive. 

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