scholarly journals Influence flame speed and flame thickness on completeness of combustion hythane

2020 ◽  
Vol 734 ◽  
pp. 012188
Author(s):  
A P Shaikin ◽  
I R Galiev ◽  
V E Epishkin
Keyword(s):  
Flame Speed ◽  
Flame Thickness

Theory of premixed-flame propagation in large-scale turbulence

1979 ◽  
Vol 90 (3) ◽  
pp. 589-604 ◽  
Author(s):  
P. Clavin ◽  
F. A. Williams
Keyword(s):  
Diffusion Approximation ◽  
Laminar Flame ◽  
Turbulent Transport ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Longitudinal Displacement ◽  
Turbulent Fluctuations ◽  
First Order ◽  
Flame Thickness ◽  
Scale Ratio

A statistical theory is developed for the structure and propagation velocity of premixed flames in turbulent flows with scales large compared with the laminar flame thickness. The analysis, free of usual closure assumptions, involves a regular perturbation for small values of the ratio of laminar flame thickness to turbulence scale, termed the scale ratio ε, and a singular perturbation for large values of the non-dimensional activation temperature β. Any effects of the flame on the flow are considered to be given. In this initial study, molecular coefficients for diffusion of heat and reactants are set equal. The results identify convective-diffusive and reactive-diffusive zones in the flame and predict thickening of the flame by turbulence through streamwise displacement of the reactive-diffusive zone. Profiles for intensities of temperature fluctuations and for streamwise turbulent transport are obtained. A fundamental quantity occurring in the analysis is the longitudinal displacement of the reactive-diffusive zone in an Eulerian frame by turbulent fluctuations, and to first order in the scale ratio this equals the longitudinal displacement of fluid elements in an Eulerian frame by turbulent fluctuations, herein termed simply the Eulerian displacement. To first order in the scale ratio it is found that, if the Eulerian displacement experiences the same type of statistical non-stationarity as the corresponding Lagrangian displacement, then the diffusion approximation is valid for streamwise turbulent transport but the turbulent flame thickens as time increases, while if the Eulerian displacement is statistically stationary then the diffusion approximation necessitates a negative coefficient of diffusion in part of the flame but the flame thickness remains constant. By carrying the analysis to second order in the scale ratio it is shown that the turbulent-flame speed exceeds the laminar-flame speed by an amount proportional to the mean square of the transverse gradient of the Eulerian displacement. This result can be understood from the mechanistic viewpoint of a wrinkled laminar flame in terms of the increase in flame area produced by turbulence. Thus the theory provides a precise statistical quantification of the model of the wrinkled laminar flame for describing structures of turbulent flames.

Direct numerical simulations of a high Karlovitz number laboratory premixed jet flame – an analysis of flame stretch and flame thickening

2017 ◽  
Vol 815 ◽  
pp. 511-536 ◽  
Author(s):  
Haiou Wang ◽  
Evatt R. Hawkes ◽  
Jacqueline H. Chen ◽  
Bo Zhou ◽  
Zhongshan Li ◽  
...  
Keyword(s):  
Reference Frames ◽  
Flame Speed ◽  
Rate Of Change ◽  
Tangential Strain ◽  
Detailed Chemistry ◽  
Jet Flame ◽  
Flame Thickness ◽  
Flame Stretch ◽  
High Karlovitz Number ◽  
Good Agreement

This article reports an analysis of the first detailed chemistry direct numerical simulation (DNS) of a high Karlovitz number laboratory premixed flame. The DNS results are first compared with those from laser-based diagnostics with good agreement. The subsequent analysis focuses on a detailed investigation of the flame area, its local thickness and their rates of change in isosurface following reference frames, quantities that are intimately connected. The net flame stretch is demonstrated to be a small residual of large competing terms: the positive tangential strain term and the negative curvature stretch term. The latter is found to be driven by flame speed–curvature correlations and dominated in net by low probability highly curved regions. Flame thickening is demonstrated to be substantial on average, while local regions of flame thinning are also observed. The rate of change of the flame thickness (as measured by the scalar gradient magnitude) is demonstrated, analogously to flame stretch, to be a competition between straining tending to increase gradients and flame speed variations in the normal direction tending to decrease them. The flame stretch and flame thickness analyses are connected by the observation that high positive tangential strain rate regions generally correspond with low curvature regions; these regions tend to be positively stretched in net and are relatively thinner compared with other regions. High curvature magnitude regions (both positive and negative) generally correspond with lower tangential strain; these regions are in net negatively stretched and thickened substantially.

scholarly journals The influence of diffusion on flame propagation

1949 ◽  
Vol 196 (1044) ◽  
pp. 105-113 ◽  
Keyword(s):  
Reaction Zone ◽  
Flame Propagation ◽  
Exothermic Reaction ◽  
Flame Speed ◽  
Heating Zone ◽  
Hydrogen Atoms ◽  
Flame Thickness ◽  
Thermal Mechanism ◽  
Free Hydrogen ◽  
Experimental Values

In stationary pre-mixed flames of hydrocarbons at pressures between 1 atm. and a few mm. the thickness of the reaction zone varies approximately inversely with the pressure, and the flame speed is independent of pressure. Marked exothermic reaction begins around 700 to 800° C, and the time of passage through the pre-heating zone is very much less than the induction period for ignition at this temperature; a purely thermal mechanism of flame propagation is inadequate. The thickness of the reaction zone is related to the distance which free hydrogen atoms may diffuse against the gas stream. Calculations are made on the relation between rates of diffusion, flame thickness and flame speed, and are compared with experimental values. It appears that diffusion of free atoms or radicals can account for flame propagation satisfactorily; the correct relation that the flame speed is nearly independent of pressure is obtained.

Flame Speed and Deflagration-Detonation Analysis in Flare Stack and Header

2018 ◽  
Author(s):  
Philip Diwakar ◽  
Jaleel Valappil
Keyword(s):  
Ambient Air ◽  
Flame Speed ◽  
Safety Concerns ◽  
Deflagration To Detonation Transition ◽  
Detonation Transition

This paper examines safety concerns related to flame speeds when warm relief gas snuffs out the pilot at the flare stack and pulls in ambient air and a spark ignites the vapor in the header. The flame speed essentially determines if the propagating flame speed is a deflagration or a detonation based on whether its subsonic or supersonic. While pipes are sized for deflagrations, they need to be analyzed and tested for detonation pressures and temperatures. Transient CFD calculations help determine the flame speeds, deflagration to detonation transition, pressures and temperatures are compared to pipe specifications and help determine if a detonation leads to a Loss of Containment and suggests mitigations.

Quantifying the role of Darrieus–Landau instability in turbulent premixed flame speed determination at various burner sizes

2021 ◽  
Vol 33 (2) ◽  
pp. 025104
Author(s):  
Xin Wang ◽  
Xiaobei Cheng ◽  
Hao Lu ◽  
Yishu Xu ◽  
Yang Liu ◽  
...  
Keyword(s):  
Flame Speed ◽  
Premixed Flame ◽  
Turbulent Premixed Flame ◽  
Landau Instability ◽  
Turbulent Premixed

scholarly journals Numerical Investigation of Pressure Influence on the Confined Turbulent Boundary Layer Flashback Process

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 146 ◽  
Author(s):  
Aaron Endres ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Gas Turbines ◽  
Separation Zone ◽  
Turbulent Flame ◽  
Pressure Rise ◽  
Flame Speed ◽  
Zone Size ◽  
Detailed Chemical Kinetics ◽  
Turbulent Flame Speed ◽  
Quenching Distance

Boundary layer flashback from the combustion chamber into the premixing section is a threat associated with the premixed combustion of hydrogen-containing fuels in gas turbines. In this study, the effect of pressure on the confined flashback behaviour of hydrogen-air flames was investigated numerically. This was done by means of large eddy simulations with finite rate chemistry as well as detailed chemical kinetics and diffusion models at pressures between 0 . 5 and 3 . It was found that the flashback propensity increases with increasing pressure. The separation zone size and the turbulent flame speed at flashback conditions decrease with increasing pressure, which decreases flashback propensity. At the same time the quenching distance decreases with increasing pressure, which increases flashback propensity. It is not possible to predict the occurrence of boundary layer flashback based on the turbulent flame speed or the ratio of separation zone size to quenching distance alone. Instead the interaction of all effects has to be accounted for when modelling boundary layer flashback. It was further found that the pressure rise ahead of the flame cannot be approximated by one-dimensional analyses and that the assumptions of the boundary layer theory are not satisfied during confined boundary layer flashback.

The Influence of Singlet Oxygen and Ozone on the Combustion in Methane-Air Mixture

2013 ◽  
Vol 699 ◽  
pp. 111-118
Author(s):  
Rui Shi ◽  
Chang Hui Wang ◽  
Yan Nan Chang
Keyword(s):  
Singlet Oxygen ◽  
Chemical Kinetics ◽  
Mole Fraction ◽  
Ignition Delay ◽  
Delay Time ◽  
Ignition Delay Time ◽  
Laminar Flame ◽  
Combustion Products ◽  
Flame Speed ◽  
Air Mixing

Based on GRI3.0, we study the main chemical kinetics process about reactions of singlet oxygen O2(a1Δg) and ozone O3 with methane-air combustion products, inherit and further develop research in chemical kinetics process with enhancement effects on methane-air mixed combustion by these two molecules. In addition, influence of these two molecules on ignition delay time and flame speed of laminar mixture are considered in our numerical simulation research. This study validates the calculation of this model which cotains these two active molecules by using experimental data of ignition delay time and the speed of laminar flame propagation. In CH4-air mixing laminar combustion under fuel-lean condition(ф=0.5), flame speed will be increased, and singlet oxygen with 10% of mole fraction increases it by 80.34%, while ozone with 10% mole fraction increase it by 127.96%. It mainly because active atoms and groups(O, H, OH, CH3, CH2O, CH3O, etc) will be increased a lot after adding active molecules in the initial stage, and chain reaction be reacted greatly, inducing shortening of reaction time and accelerating of flame speed. Under fuel rich(ф=1.5), accelerating of flame speed will be weakened slightly, singlet oxygen with 10% in molecular oxygen increase it by 48.93%, while ozone with 10% increase it by 70.25%.

Sign in / Sign up

Export Citation Format

Share Document