Mechanistic interpretation and modelling

The ignition limit is a feature of systems containing approximately 0.5% H2 or more. If we begin the discussion by imagining a pure H2 -I- O2 system in which the H2 is then systematically replaced by CO, we find initially that the (second) limit moves to lower ambient temperatures and higher pressures. This feature can be modelled quantitatively simply by including the relative third body effect of CO, which is less than 1 (i.e., CO is a less 

A further replacement of H2 with CO sees the limit moving back to higher ambient temperature, as indicated in the figure. This inhibitory effect arises for systems with low [H2] for which the extra termination step (10) involving CO becomes able to compete with the branching process (3). Using the reactions 

The complex periodicities in the CO + O2 reaction are only now yielding to simulation, but are again arising from a mechanism based on an H2 -I- O2 scheme with the few steps involving CO described above. 

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