Structure of n-heptane/air triple flames in partially-premixed mixing layers

Abstract

Results of a detailed numerical analysis of an n-heptane/air edge flame are presented. The equations of a low-Mach number reacting flow are solved in a two-dimensional domain using detailed models for species transport and chemical reactions. The reaction mechanism involves 560 species and 2538 reversible reactions. We consider an edge flame that is established in a mixing layer with a uniform velocity field. The mixing layer spans the equivalence ratios between pure air and 3.5. The detailed model enables us to analyze the chemical structure of the n-heptane edge flame. We identify major species profiles, discuss reactions causing the heat-release, and exploit Computational Singular Perturbation (CSP) to discuss the main fuel-consumption pathways and the structure of explosive modes in the edge flame. This analysis is performed for several regions in the edge flame to discuss the different processes at work in the premixed branches and the trailing diffusion flame. We compare different cuts through the 2D edge flame to canonical 1D premixed and diffusion flames. We also analyze the accuracy of a skeletal mechanism which was previously developed using CSP from homogeneous ignition calculations of n-heptane and show that a significant reduction in size of the mechanism can be achieved without a significant decrease in accuracy of the edge flame computation. This skeletal mechanism is then used to study the effects of increasing the equivalence ratio in the partially-premixed fuel stream.

Algorithmic Analysis of Chemical Dynamics of the Autoignition of NH3–H2O2/Air Mixtures

“…. , 2K [21,22,24,33,[48][49][50][51]. Since by definition f n > 0, positive (negative) values of P n k indicate a contribution of the k-th process towards strengthening (weakening) the impact of the n-th mode.…”

Autoignition dynamics of DME/air and EtOH/air homogeneous mixtures

“…(6)- (9) show that J e k ¼ ÀJ eþ1 k ; P e k ¼ ÀP eþ1 k and D e n ¼ ÀD eþ1 nþ1 ; k ¼ 1; 2K. The API and Po tools have been used extensively in the context of the CSP analysis; e.g., from the early studies of homogeneous methanol oxidation [40], of methane flames [45], of the transient flame-vortex interaction [46] and of the two-stage ignition of large hydrocarbons [47], to the more recent analysis of the methane-air edge flame structure [48], of the n-heptane/air triple flames structure in partially-premixed mixing layers [49] and of flame dynamics in a mesoscale channel [50]. These two tools were also employed along with TPI for the analysis of modes related to fast exhausted time scales or to the characteristic dissipative or explosive time scale [17][18][19][20][21][22][23][24].…”

A conservative, thermodynamically consistent numerical approach for low Mach number combustion. Part I: Single-level integration

“…Our definition of enthalpy includes the standard enthalpy of formation, so there is no net change to h due to reactions. Summing the species equations and noting that m Y m = 1 and mω m = 0, we see that (2) implies the continuity equation,…”

“…Step 4d: (Chemistry integration) Use the VODE [28] package to integrate species (2) and enthalpy (3) over t to advance (ρY, ρh) n to (ρY, ρh) (k) using the advection/diffusion source terms, Q…”

“…Low Mach number numerical simulation methodology provides a valuable tool for efficiently modelling reacting flow with detailed kinetics and transport; see [1][2][3][4][5][6][7][8] for a variety of recent studies. Low Mach number models are derived from fully compressible equations using low Mach number asymptotics [9,10] and do not include acoustic wave propagation, allowing for much larger time steps based on an advective CFL condition.…”