(2-10) Towards Evaluation of Turbulent Flame Speed((SI-4)S. I. Engine Combustion 4-Flame Propagation)

The paper presents the computational fluid dynamics (CFD) combustion modeling approach based on two combustion models. This modeling approach was applied to a hydrogen deflagration experiment conducted in a large-scale confined experimental vessel. The used combustion models were Zimont's turbulent flame-speed closure (TFC) model and Lipatnikov's flame-speed closure (FSC) model. The conducted simulations are aimed to aid identifying and evaluating the potential hydrogen risks in nuclear power plant (NPP) containment. The simulation results show good agreement with experiment for axial flame propagation using the Lipatnikov combustion model. However, substantial overprediction in radial flame propagation is observed using both combustion models, which consequently results also in overprediction of the pressure increase rate and overall combustion energy output. As assumed for a large-scale experiment without any turbulence inducing structures, the combustion took place in low-turbulence regimes, where the Lipatnikov combustion model, due to its inclusion of quasi-laminar source term, has advantage over the Zimont model.

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Large-Scale Homogeneous Hydrogen-Air-Steam Deflagration Experiment Simulated Using Two Turbulent Flame Speed Closure Models

Volume 5: Student Paper Competition ◽

10.1115/icone24-60134 ◽

2016 ◽

Author(s):

Tadej Holler ◽

Varun Jain ◽

Ed M. J. Komen ◽

Ivo Kljenak

Keyword(s):

Flame Propagation ◽

Nuclear Power ◽

Large Scale ◽

Turbulent Flame ◽

Turbulent Flames ◽

Flame Speed ◽

Energy Output ◽

Combustion Model ◽

Turbulent Flame Speed ◽

Combustion Models

The CFD combustion modeling approach based on two combustion models was applied to a hydrogen deflagration experiment conducted in a large-scale confined experimental vessel. The used combustion models were Zimont’s Turbulent Flames Speed Closure (TFC) model and Lipatnikov’s Flame Speed Closure (FSC) model. The conducted simulations are aimed to aid identifying and evaluating the potential hydrogen risks in Nuclear Power Plant (NPP) containment. The simulation results show good agreement with experiment for axial flame propagation using the Lipatnikov combustion model. However substantial overprediction in radial flame propagation is observed using both combustion models, which consequently results also in overprediction of the pressure increase rate and overall combustion energy output. As assumed for a large-scale experiment without any turbulence inducing structures, the combustion took place in low-turbulence regimes, where the Lipatnikov combustion model, due to its inclusion of quasi-laminar source term, has advantage over the Zimont model.

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Effect of Centrifugal Force on Conventional and Alternative Fuel Surrogate Turbulent Premixed Flames

Volume 3A: Coal, Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration ◽

10.1115/gt2014-27327 ◽

2014 ◽

Cited By ~ 1

Author(s):

Alejandro M. Briones ◽

Balu Sekar ◽

Timothy Erdmann

Keyword(s):

Flame Front ◽

Centrifugal Force ◽

Flame Propagation ◽

Propagation Velocity ◽

Turbulent Flame ◽

Premixed Flames ◽

Flame Speed ◽

Turbulent Premixed Flames ◽

Flame Propagation Velocity ◽

Turbulent Flame Speed

The effect of centrifugal force on flame propagation velocity of stoichiometric propane-, kerosene-, and n-octane-air turbulent premixed flames was numerically examined. The quasi-turbulent numerical model was set in an unsteady two-dimensional geometry with finite length in the transverse and streamwise directions but with infinite length in the spanwise direction. There was relatively good comparison between literature-reported measurements and predictions of propane-air flame propagation velocity as a function of centrifugal force. It was found that for all mixtures the flame propagation velocity increases with centrifugal force. It reaches a maximum then falls off rapidly with further increases in centrifugal force. The results of this numerical study suggest there are no distinct differences among the three mixtures in terms of the effect of centrifugal force on the flame propagation velocity. There are, however, quantitative differences. The numerical models are set in a non-inertial, rotating reference frame. This rotation imposes a radially outward (centrifugal) force. The ignited mixture at one end of the tube raises the temperature and its heat release tends to laminarize the flow. The attained density difference combined with the direction of the centrifugal force promotes Rayleigh-Taylor instability. This instability with thermal expansion and turbulent flame speed constitute the flame propagation mechanism towards the other tube end. A wave is also originated but propagates faster than the flame. During propagation the flame interacts with eddies that wrinkle and/or corrugate the flame. The flame front wrinkles interact with streamtubes that enhance Landau-Darrieus (hydrodynamic) instability, giving rise to a corrugated flame. Under strong stretch conditions the stabilizing equidiffusive-curvature mechanism fails and the flame front breaks up, allowing inflow of unburned mixture into the flame. This phenomenon slows down the flame temporarily and then the flame speeds up faster than before. However, if corrugation is large and the inflow of unburned mixture into the flame is excessive, the latter locally quenches and slows down the flame. This occurs when the centrifugal force is large, tending to blowout the flame. The wave in the tube interacts continuously with the flame through baroclinic torques at the flame front that further enhances the above mentioned flame-eddies interactions. Only at low centrifugal forces the wave intermingles several times with the flame before the averaged flame propagation velocity is determined. The centrifugal force does not substantially increase the turbulent flame speed as commented by previous experimental investigations. The results also suggest that an ultra-compact combustor (UCC) with high-g cavity (HGC) will be limited to centrifugal force levels in the 2000–3000g range.

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Turbulent Flame Speed as an Indicator for Flashback Propensity of Hydrogen-Rich Fuel Gases

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4025068 ◽

2013 ◽

Vol 135 (11) ◽

Cited By ~ 14

Author(s):

Yu-Chun Lin ◽

Salvatore Daniele ◽

Peter Jansohn ◽

Konstantinos Boulouchos

Keyword(s):

Gas Turbine ◽

Flame Propagation ◽

Carbon Capture ◽

Turbulent Flame ◽

Flame Speed ◽

Turbulent Flame Speed ◽

Velocity Gradients ◽

Fuel Mixtures ◽

Operational Range ◽

Rich Mixtures

The turbulent flame speed (ST) is proposed to be an indicator of the flashback propensity for hydrogen-rich fuel gases at gas turbine relevant conditions. Flashback is an inevitable issue to be concerned about when introducing fuel gases containing high hydrogen content to gas turbine engines, which are conventionally fueled with natural gas. These hydrogen-containing fuel gases are present in the process of the integrated gasification combined cycle (IGCC), with and without precombustion carbon capture, and both syngas (H2 + CO) and hydrogen with various degrees of inert dilution fall in this category. Thus, a greater understanding of the flashback phenomenon for these mixtures is necessary in order to evolve the IGCC concept (either with or without carbon capture) into a promising candidate for clean power generation. Compared to syngas, the hydrogen-rich fuel mixtures exhibit an even narrower operational envelope between the occurrence of lean blow out and flashback. When flashback occurs, the flame propagation is found to occur exclusively in the boundary layer of the pipe supplying the premixed fuel/air mixture to the combustor. This finding is based on the experimental investigation of turbulent lean-premixed nonswirled confined jet flames for three fuel mixtures with H2 > 70 vol. %. Measurements were performed up to 10 bar at a fixed bulk velocity at the combustor inlet (u0 = 40 m/s) and preheat temperature (T0 = 623 K). Flame front characteristics were retrieved via planar laser-induced fluorescence of the hydroxyl radical (OH-PLIF) diagnostics and the turbulent flame speed (ST) was derived, accordingly, from the perspective of a global consumption rate. Concerning the flashback limit, the operational range of the hydrogen-rich mixtures is found to be well represented by the velocity gradients prescribed by the flame (gc) and the flow (gf), respectively. The former (gc) is determined as ST/(Le × δL0), where Le is the Lewis number and δL0 is the calculated thermal thickness of the one-dimensional laminar flame. The latter (gf) is predicted by the Blasius correlation for fully developed turbulent pipe flow and it indicates the capability with which the flow can counteract the opposed flame propagation. Our results show that the equivalence ratios at which the two velocity gradients reach similar levels correspond well to the flashback limits observed at various pressures. The methodology is also found to be capable of predicting the aforementioned difference in the operational range between syngas and hydrogen-rich mixtures.

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Influence of Turbulent Scalar Mixing Physics on Premixed Flame Propagation

Journal of Combustion ◽

10.1155/2011/451351 ◽

2011 ◽

Vol 2011 ◽

pp. 1-8 ◽

Cited By ~ 6

Author(s):

H. Kolla ◽

N. Swaminathan

Keyword(s):

Direct Effect ◽

Flame Propagation ◽

Indirect Effect ◽

Turbulent Flame ◽

Quantitative Difference ◽

Flame Speed ◽

Premixed Flame ◽

Scalar Mixing ◽

Turbulent Flame Speed ◽

Reactive Scalar

The influence of reactive scalar mixing physics on turbulent premixed flame propagation is studied, within the framework of turbulent flame speed modelling, by comparing predictive ability of two algebraic flame speed models: one that includes all relevant physics and the other ignoring dilatation effects on reactive scalar mixing. This study is an extension of a previous work analysing and validating the former model. The latter is obtained by neglecting modelling terms that include dilatation effects: a direct effect because of density change across the flame front and an indirect effect due to dilatation on turbulence-scalar interaction. An analysis of the limiting behaviour shows that neglecting the indirect effect alters the flame speed scaling considerably when is small and the scaling remains unaffected when is large. This is evident from comparisons of the two models with experimental data which show that the quantitative difference between the two models is as high as 66% at but only 4% at . Furthermore, neglecting the direct effect results in a poor prediction of turbulent flame speed for all values of , and both effects are important for practically relevant values of this velocity ratio.

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Turbulent Flame Speed as an Indicator for Flashback Propensity of Hydrogen-Rich Fuel Gases

Volume 1B: Combustion, Fuels and Emissions ◽

10.1115/gt2013-95518 ◽

2013 ◽

Cited By ~ 1

Author(s):

Y.-C. Lin ◽

S. Daniele ◽

P. Jansohn ◽

K. Boulouchos

Keyword(s):

Gas Turbine ◽

Flame Propagation ◽

Carbon Capture ◽

Turbulent Flame ◽

Flame Speed ◽

Turbulent Flame Speed ◽

Velocity Gradients ◽

Fuel Mixtures ◽

Operational Range ◽

Rich Mixtures

The turbulent flame speed (ST) is proposed to be an indicator of flashback propensity for hydrogen-rich fuel gases at gas turbine relevant conditions. Flashback is an inevitable issue to be concerned about when introducing fuel gases containing high hydrogen content to gas turbine engines, which are conventionally fueled with natural gas. These hydrogen-containing fuel gases are present in the process of the integrated gasification combined cycle (IGCC) with and without pre-combustion carbon capture, and both syngas (H2 + CO) and hydrogen with various degree of inert dilution fall in this category. More understanding on the flashback phenomenon for these mixtures is thus necessary in order to evolve the IGCC concept (either with or without carbon capture) into a promising candidate for clean power generation. Compared to syngas, the hydrogen-rich fuel mixtures exhibit an even narrower operational envelope between the occurrence of lean blow out and flashback. When flashback occurs, the flame propagation is found to happen exclusively in the boundary layer of the pipe supplying the premixed fuel/air mixture to the combustor. This finding is based on the experimental investigation of turbulent, lean-premixed, non-swirled, confined jet flames for three fuel mixtures with H2 > 70 Vol. %. Measurements were performed up to 10 bar at fixed bulk velocity at the combustor inlet (u0 = 40 m/s) and preheat temperature (T0 = 623 K). Flame front characteristics were retrieved via OH-PLIF diagnostics, and turbulent flame speed (ST) was derived accordingly from the perspective of a global consumption rate. Concerning the flashback limit, the operational range of the hydrogen-rich mixtures is found to be well represented by the velocity gradients prescribed respectively by the flame (gc) and the flow (gf). The former (gc) is determined as ST/(Le × δL0), where Le is the Lewis number and δL0 is the calculated thermal thickness of the one-dimensional laminar flame. The latter (gf) is predicted by the Blasius correlation for fully developed turbulent pipe flow, and it indicates the capability with which the flow can counteract the opposed flame propagation. Our results show that the equivalence ratios at which the two velocity gradients reach similar levels correspond well to the flashback limits observed at various pressures. The methodology is also found to be capable of predicting the aforementioned difference in the operational range between syngas and hydrogen-rich mixtures.

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

Fluids ◽

10.3390/fluids4030146 ◽

2019 ◽

Vol 4 (3) ◽

pp. 146 ◽

Cited By ~ 2

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.

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