Exploring flux representations of complex kinetics networks

Abstract

in Wiley Online Library (wileyonlinelibrary.com).To extract meaningful information from complex kinetic models involving a large number of species and reactions, advanced computational techniques are required. In this work, new approaches have been proposed based on element flux calculations for systematic kinetic analysis of complex reaction models. These approaches quantify element transformation flux between species to determine a metric that accurately captures the production and consumption of species. Furthermore, a graph searching procedure is employed to retrieve all possible reaction pathways from the highly complex reaction networks. Element fluxes involved in these pathways provide an indicator to quantitatively evaluate pathway activities. Based on pathway activities, a novel approach is proposed to project the totality of the information contained in pathway weights onto a single scalar, reactivity status indicator, which enables a compact representation of local chemistry. The proposed approaches are illustrated with highly complex kinetic mechanisms describing oxidation of n-pentane, n-heptane, and a biodiesel surrogate methyl-butanoate.

Skeletal Mechanism Generation for High-Temperature Combustion of H2/CO/C1–C4 Hydrocarbons

“…In element flux analysis, the instantaneous element flux for each element (such as C) from species k 1 to k 2 through reaction i , denoted as Ȧ i , k 1→ k 2 ( t ), is calculated via Ȧ i , k 1 → k 2 ( t ) = q i ( t ) N A , k 1 N A , k 2 N A , i where q i ( t ) is the instantaneous reaction rate of reaction i at time t , N A , k 1 , N A , k 2 , and N A , i are the number of atom A in species k 1, species k 2, and reaction i , respectively. For a mechanism consisting of I elementary reactions and K species, the total transformation for element A from species k 1 to k 2 at instantaneous time t can be obtained via the summation of contributions from all reactions. Ȧ k 1 → k 2 ( t ) = prefix∑ i = 1 I Ȧ i , k 1 → k 2 false( t false) To derive global reaction path information, a time- or space-integrated flux indicator should be used, e.g., the time-integrated flux during ignition simulations in the present work A ̇ ̅ k 1 → k 2 = prefix∫ 0 τ Ȧ k 1 → k 2 false( t false) …”

“…Figure 7. Predicted laminar flame speed versus equivalence ratio for nheptane and n-dodecane using the reduced mechanism (the simplified model proposed by You et al36 combined with the resulting skeletal mechanism in the present work). Lines represent numerical simulation results, and symbols represent experimental results from Ji et al45 …”

Analysis of Combustion Characteristics When Adding Hydrogen and Short-Chain Hydrocarbons to RP-3 Aviation Kerosene Based on the Variation Disturbance Method

“…Time-Integrated Element Flux Analysis. Element flux analysis was developed by Revel et al, 33 and Androulakis et al 34,35 proposed a time-integrated element flux analysis for analyzing the reaction path during the combustion process of the fuel. The method has been widely used in the analysis of combustion dynamics.…”

Skeletal Kinetic Model Generation for the Combustion of C₁-C₂ Fuels

“…Time-integrated element flux analysis provides a simple method to identify reaction paths connecting different species 36,37 . The method is briefly outlined as following.…”

“…Mechanism reductions are carried out with an automatic mechanism reduction program ReaxRed 39 , to generate skeletal mechanisms with a given simulation error. To achieve a skeletal mechanism that is able to describe ignition delay times of CH4, CH3OH, CH2O, C2H2, C2H4, C2H6, C2H5OH, and CH3CHO, auto-ignition processes with constant pressure in a homogeneous reactor for a mixture of these eight fuels with equal proportion are simulated with SENKIN 37 . Sampling points required in mechanism reduction are taken from simulation results near ignition time with pressure from 1.01 × 10 5 to 3.04 × 10 6 Pa, equivalence ratio from 0.5 to 2.0, and initial temperature from 800-1600 K. H radical is selected as the target species in the employed reduction methods following Ref.26 since it is one of the most important species in combustion processes of all these fuels.…”