THE NECESSITY OF USING DETAILED KINETICS IN MODELS FOR PREMIXED COMBUSTION WITHIN POROUS-MEDIA

Models for premixed combustion within porous inert media (PIM) are com plicated by the highly nonlinear radiative exchange terms in the energ y equation for the solid matrix in addition to the stiffness of the se t of gas phase equations. Therefore, prior researchers have simulated the gas-phase reactions using single-step chemistry. In the present wo rk, predictions are made using both single-step and multistep kinetics mechanisms. It is concluded that it is essential to use multistep kin etics if accurate predictions of the temperature distributions, energy release rates, and total energy release are sought. Obviously, this i s also true if predictions of the composition profiles and emissions a re sought. Single-step kinetics is shown to be adequate for predicting all the flame characteristics except the emissions for the very lean conditions under which equilibrium favors the more complete combustion process dictated by global chemistry. The first predictions of NO and CO emissions from PIM burners are presented and compared with experim ental data. The model predicts the CO emissions very accurately and pr edicts the NO trend correctly but overpredicts the NO emissions for ph i > 0.8. The present multistep PIM burner model does not accurately re produce the data for the burning speed and NO emissions for nondilute mixtures. These discrepancies can be only partially attributed to expe rimental uncertainties and/or imprecise knowledge of the properties of the solid matrix. Thus, it is concluded that important aspects of the physical processes within PIM combustors are not well simulated at pr esent.