Investigation of the correlation of sensitivity vectors of hydrogen combustion models

A well‐established method for the analysis of large reaction mechanisms is the calculation and interpretation of the sensitivity of the kinetic model output Y_i to parameter changes. Comparison of the sensitivity vectors s _i = {? Y_i/? p } belonging to different model outputs is a new tool for kinetic analysis. The relationship of the sensitivity vectors was investigated in homogeneous explosions, freely propagating and burner‐stabilized laminar flames of hydrogen–air mixtures, using either calculated adiabatic or constrained temperature profiles, for fuel‐to‐air ratios φ = 0.5–4.0. Sensitivity vectors are called locally similar, if the relationship s _i = λ_ij s _j is valid, where λ_ij is a scalar. In many systems, only approximate local similarity of the sensitivity vectors exists and the extent of it can be quantified by using an appropriate correlation function. In the cases of adiabatic explosions and burner‐stabilized flames, accurate local similarity was present in wide ranges of the independent variable (time or distance), and the correlation function indicated that the local similarity was not valid near the concentration extremes of the corresponding species. The regions of poor similarity were studied further by cobweb plots. The correlation relationships found could be interpreted by the various kinetic processes in the hydrogen combustion systems. The sensitivity vector of the laminar flame velocity is usually considered to be characteristic for the whole combustion process. Our investigations showed that the flame velocity sensitivity vector has good correlation with the H and H₂O concentration sensitivities at the front of the adiabatic flames, but there is poor correlation with the sensitivity vectors of all concentrations in homogeneous explosions. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 238–252 2004