The quality of kinetic data

In the previous sections we have reviewed very briefly the main features of the techniques used to obtain kinetics data for modelling combustion processes, emphasizing the factors limiting their range and the quality of data derived from them. The same factors are among those that must be considered when the data are being assessed. 

The experimental techniques reviewed are potentially capable of producing good precision rate data from sub-ambient temperatures to 3000 K and beyond, and of covering a wide pressure range. Despite that, the quality of the data available for modelling leaves a lot to be desired. The main problems encountered are  

There are many reactions which, on good chemical grounds, are postulated to occur in combustion processes but for which there are no measured rate data. In some cases this may be due to the lack of a convenient source of the species involved but often this is not so. Techniques for studying the reactions exist but the financial resources have not been made available to do so. This same resource limitation often applies also to extending existing measurements into regions of temperature and pressure pertinent to combustion processes. 

When experimental data are lacking recourse must be made to theory and estimation methods (Section 3.4). 

Although a standard deviation of about 10% is now quite usual for rate constant measurements from fast-flow discharge and pulsed photolysis studies, it is still found that the same reaction studied in different laboratories by the same technique may give results of similar precision, but which differ by far more than would be expected on the basis of that precision. Potential sources of such discrepancies are many but, with experience, likely errors can sometimes be identified in particular cases. For example, reactions between short lived radical intermediates are common in combustion processes. The measurement of the rate constants of such reactions, where the reaction is second order with respect to the transient species, pose particular but well recognized difficulties stemming from the need to determine the absolute concentration of the reacting radical (Chapter 1). This is difficult to achieve and has been a common source of error in this type of determination as exemplified in the series of studies on the rate of the reaction CHO -I- CHO — CH2O -H CO. 

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