Mechanism reduction without time-scale analysis

6 MECHANISM REDUCTION WITHOUT TIME-SCALE ANALYSIS 

The wording full mechanism and reduced mechanism suggests that there are full mechanisms which include all species present in the reactor, and that the model includes all significant reactions. It is easy to see that this is not true for several reasons. The quantum state of molecules and radicals is almost never considered in complex chemical models. Examples of rare exceptions are the distinctions between CH2(X Bi) and CH2(a Ai) in combustion and between 0( P) and 0( D) in atmospheric chemistry. All species in complex mechanisms are effectively lumped, since molecules are treated as single species with a Boltzman distribution of quantum states. In many cases isomers are also considered as identical species. 

Detailed kinetic models almost never include all species that are known to be present in the reactor. As an example, it is well known to everyone who has used a gas chromatograph with a flame-ionization detector, that ions are present in hydrocarbon flames. However, mechanisms for methane flames do not, in general, include the reactions of ions. The fact is that implicitly reduced mechanisms are used more often than not in modelling work understanding how objectively reduced mechanisms can be generated is, therefore, of primary importance. 

it is not true that full mechanisms are universally applicable. All detailed mechanisms have a domain of applicability in temperature, pressure and initial concentration space. They are constructed in such a way as to fulfil certain requirements. For example, they may be required to reproduce some experimental concentration or temperature profiles, or experimental features such as ignition times. Although the mechanisms claimed to be general or full are already tailored to a domain of assumed applications, they still usually contain many species and reactions. 

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Mechanism reduction without time-scale analysis... 

Mechanism reduction without time-scale analysis The normalized temperature rate sensitivity is given by... 

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