Small-scale superadiabatic combustors with a two-step chain-branching chemistry model: Asymptotic models and the effect of two-dimensionality on lean mixtures burning

Abstract

Small-sized super-adiabatic combustion devices consisting of countercurrent channels with heat-exchange segments are investigated for their ability to burn ultra-lean mixtures. The study is carried out numerically using a two-step chain-branching kinetic model in which the flammability limit appears explicitly. Various asymptotic approximations for modeling the process are considered, together with the solution of the two-dimensional conservation equations for species and temperature in the gas and the solid walls. The influence of the width of the channels and the separating walls properties on the efficiency of the device in burning mixtures below the flammability limit is investigated. The main goal of the study is to determine the applicability of the considered asymptotic models for the effective prediction of the operation of such combustion devices. Novelty and significance statementThe study contains a demonstration of the possibility of burning ultra-lean mixtures in counterflow type combustion devices consisting of a system of parallel channels, using a two-step chain-branching kinetic model. A number of model asymptotic approximations and areas of their applicability are investigated. In particular, the present study considers finite width for the channels and the separating walls and the results are compared satisfactorily to previous papers of the same authors were the one-dimensional narrow channel approximation was used, validating in this way this approximation. The results of the study may be of importance for the design of small-scale combustion devices used for generating energy in remote conditions.