A DNS study of extreme and leading points in lean hydrogen-air turbulent flames – Part I: Local thermochemical structure and reaction rates
Journal article, 2022

A Direct Numerical Simulation (DNS) study of statistically one-dimensional and planar, lean complex-chemistry hydrogen-air flames characterized by a low Lewis number Le and three different Karlovitz numbersKa ranging from 3 to 33 is performed, with the same complex-chemistry flames being also simulated by setting molecular diffusivities of all species equal to the heat diffusivity of the mixture. The simulations predict a significant increase in a ratio of turbulent burning velocity to the laminar flame speed in the former (Le<1) flames when compared to the latter (equidiffusive) flames. Extreme points characterized by the peak (over the computational domain) Fuel Consumption Rate (FCR) or Heat Release Rate (HRR) are found at each instant. In the equidiffusive flames, such extreme FCR and HRR are close to their peak values in the unperturbed laminar flame. If Le is low, the former rates are significantly higher than the latter ones due to an increase in the local temperature, equivalence ratio, and radical mass fractions, caused by diffusive-thermal effects. While the studied extreme points may appear sufficiently far from the leading edge of the instantaneous flame brush, leading points characterized by a lower, but still high (Le<1) FCR or HRR are observed close to the leading edge at each instant. Various local characteristics (temperature, equivalence ratio, species mass fractions and their gradients, reaction rates, etc.) of the extreme and leading points are explored and significant differences between zones characterized by high FCR or HRR are revealed. For instance, in the latter zones, major chemical pathways are changed. Moreover, while the extreme HRRs strongly fluctuate in time, with their mean and rms values being significantly increased by Ka, the extreme FCRs fluctuate weakly and are close at different Ka, thus, implying that almost the same extreme FCR can be reached in substantially different local burning structures.

Turbulent consumption speed

Lewis number

Hydrogen

Leading point concept

Diffusive-thermal effects

DNS

Turbulent combustion

Author

Hsu Chew Lee

Southern University of Science and Technology

Peng Dai

Southern University of Science and Technology

Minping Wan

Southern University of Science and Technology

Andrei Lipatnikov

Chalmers, Mechanics and Maritime Sciences (M2), Combustion and Propulsion Systems, Combustions and Sprays

Combustion and Flame

0010-2180 (ISSN)

Vol. 235 111716

Subject Categories

Energy Engineering

Atom and Molecular Physics and Optics

Fluid Mechanics and Acoustics

DOI

10.1016/j.combustflame.2021.111716

More information

Latest update

1/19/2022