Four-step and three-step systematically reduced chemistry for wide-range H2–air combustion problems

Abstract

a b s t r a c tThe feasibility of developing multipurpose reduced chemistry that is able to describe, with sufficient accuracy, premixed and non-premixed flames, one-dimensional detonations, high-temperature autoignition, and also low-temperature autoignition is explored. A four-step mechanism with O and OH in steady state is thoroughly tested and is shown to give satisfactory results under all conditions. The possibility of reducing this to a three-step mechanism, to decrease computation times without compromising the range of applicability is then investigated. The originality of this work resides in introducing a single species X, representing either HO 2 for high-temperature ignition or H 2 O 2 for low-temperature ignition. An algorithm is defined that covers the entire range without significant degradation of accuracy. Integrations show promising results for different laminar test cases, and applicability to turbulent flows is indicated.

The chemistry involved in the third explosion limit of H2–O2 mixtures

“…1, the temperature dependence of the critical explosion pressure is seen to be predicted remarkably well by the analytical expression (21). This agreement in slope is determined largely by the activation temperatures present in (14) and (17). The predicted slight curvature is of the opposite sign from that shown in the experimental curve, but Lewis and von Elbe [3] indicate that the experimental measurements are partly extrapolated to higher pressures, and therefore it is possible that more accurate measurements would have revealed a change in the sign of the curvature.…”

“…Besides the reduction on which the present analysis is based [12], recently employed in an investigation of diffusion-flame ignition in mixing layers [13], there now are three-step and four-step descriptions that apply to wide-ranging hydrogen applications [14]. The reductions to be applied in the present work are selected to be the simplest ones that can describe the third explosion limit with reasonable accuracy.…”

Explicit formulation of the reactivity of hydrogen, methane and decane

“…As presented in our previous papers [10][11][12]22], the simplification of the characteristic polynomial, responsible for the simplicity of the analytic expressions of the eigenvalue may seem to be a lucky coincidence. Figure 7 illustrates the physical reason in the case of hydrogen, by comparing the inverse kinetic times s 1 ; s 2 and s 3 from the A matrix of Eq.…”

“…This expression has been used in [10][11][12]24] to correct departures from steadystates of O and OH during autoignition processes, in explicit reduced chemistry formulations. The same expression has been also used in [22], to offer a post-processing solution for lifted flames, by readily identifying the most reacting zones, where autoignition occurs -a method very similar to CEMA [16].…”

“…This peculiarity allowed us in the past to develop reduced chemistry models for both hydrogen and syngas, able to reproduce most combustion processes, including autoignition [9][10][11][12].…”