Development of a variational method for chemical kinetic sensitivity analysis

A new variational sensitivity analysis method has been developed and applied to chemical kinetic schemes in aeronautic combustion chambers. The method has been validated by comparison with the brute force method for hydrogen-oxygen combustion in a well stirred reactor assembly. Both methods agree very well as long as the nondimensional sensitivity coefficients are not too small. The variational method requires much less computational time than the brute force one. The method is then applied to complete kinetic schemes for methanol/oxygen and ethane/air combustion in a real well stirred reactor assembly. The reactions re-arrangement provided by the method is found to be a good tool for kinetic studies: the method may be used as a pre-processor for mechanism reductions. Results with reduced schemes for methanol (eleven reactions among the eighty-eight original ones) seems fairly good. For ethane, forty six reactions are needed for correct predictions, but the reduction could be carried out, using other chemical concepts. These results, together with the low computational times, are encouraging and the variational method may now be used to enhance kinetic studies.