Complex oscillatory ignition

Fig, 5.28. The p-T. ignition diagram for a stoichiometric 2H2 + O2 mixture with mean residence time fres = 2.0 0.2 s showing additional region of complex oscillatory ignition. (Reprinted with permission from reference [33], Royal Society of Chemistry.)... 

In order to model the oscillatory waveform and to predict the p-T locus for the (Hopf) bifurcation from oscillatory ignition to steady flame accurately, it is in fact necessary to include more reaction steps. Johnson et al. [45] examined the 35 reaction Baldwin-Walker scheme and obtained a number of reduced mechanisms from this in order to identify a minimal model capable of semi-quantitative p-T limit prediction and also of producing the complex, mixed-mode waveforms observed experimentally. The minimal scheme depends on the rate coefficient data used, with an updated set beyond that used by Chinnick et al. allowing reduction to a 10-step scheme. It is of particular interest, however, that not even the 35 reaction mechanism can predict complex oscillations unless the non-isothermal character of the reaction is included explicitly. (In computer integrations it is easy to examine the isothermal system by setting the reaction enthalpies equal to zero this allows us, in effect, to examine the behaviour supported by the chemical feedback processes in this system in isolation... 

Fig. 5.34. Traverse through region of complex ignition in Fig 5.33 for p = 40Torr (upper trace) and p = 20Torr (lower trace) showing evolution of complex oscillatory waveform. (Reprinted with permission from reference [67], American Institute of Physics.)...

Yet more complexity and variety of behaviour is found in the oxidation of hydrocarbons and related species. Such reactions again ndiibit multiplidty of ignition limits but in addition show oscillatory modes of reaction both in the slow reaction and in ignition phenomena. It is only within the past ten years that these systems have been successfully interpreted in the light of current theoretical ideas. These ideas we reserve until Section S. 

The operation of a pulse combustor is controlled by a complex interaction between an oscillatory combustion process and acoustic waves that are excited inside the combustor (Ligure 21.13). Ignition of the fuel-air mixture by a spark plug... 

The roots of spontaneous combustion studies are deeply seated in physico-chemical interactions due to non-linear kinetics, heat release and heat dissipation. Discontinuous responses to slowly varying conditions are features that are most familiar as ignition and extinction, but the transitions can also be between stationary or oscillatory states. This presentation is concerned with oscillations and multiple stabilities that owe their existence to complex thermoKinetic interactions. 

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