Hydrogen–Air–Steam Deflagration Experiment Simulated Using Different Turbulent Flame-Speed Closure Models

2018 ◽  
Vol 4 (3) ◽  
Author(s):  
Holler Tadej ◽  
Ed M. J. Komen ◽  
Kljenak Ivo
Keyword(s):  
Flame Propagation ◽  
Nuclear Power ◽  
Large Scale ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Energy Output ◽  
Combustion Model ◽  
Turbulent Flame Speed ◽  
Modeling Approach ◽  
Combustion Models

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.

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

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.

scholarly journals A Data-Driven Methodology for the Simulation of Turbulent Flame Speed across Engine-Relevant Combustion Regimes

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4210
Author(s):  
Alessandro d’Adamo ◽  
Clara Iacovano ◽  
Stefano Fontanesi
Keyword(s):  
Turbulent Combustion ◽  
Internal Combustion Engines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Data Driven ◽  
Combustion Model ◽  
Virtual Design ◽  
Turbulent Flame Speed ◽  
Combustion Models ◽  
Combustion Regimes

Turbulent combustion modelling in internal combustion engines (ICEs) is a challenging task. It is commonly synthetized by incorporating the interaction between chemical reactions and turbulent eddies into a unique term, namely turbulent flame speed sT. The task is very complex considering the variety of turbulent and chemical scales resulting from engine load/speed variations. In this scenario, advanced turbulent combustion models are asked to predict accurate burn rates under a wide range of turbulence–flame interaction regimes. The framework is further complicated by the difficulty in unambiguously evaluating in-cylinder turbulence and by the poor coherence of turbulent flame speed (sT) measurements in the literature. Finally, the simulated sT from combustion models is found to be rarely assessed in a rigorous manner. A methodology is presented to objectively measure the simulated sT by a generic combustion model over a range of engine-relevant combustion regimes, from Da = 0.5 to Da = 75 (i.e., from the thin reaction regime to wrinkled flamelets). A test case is proposed to assess steady-state burn rates under specified turbulence in a RANS modelling framework. The methodology is applied to a widely adopted combustion model (ECFM-3Z) and the comparison of the simulated sT with experimental datasets allows to identify modelling improvement areas. Dynamic functions are proposed based on turbulence intensity and Damköhler number. Finally, simulations using the improved flame speed are carried out and a satisfactory agreement of the simulation results with the experimental/theoretical correlations is found. This confirms the effectiveness and the general applicability of the methodology to any model. The use of grid/time resolution typical of ICE combustion simulations strengthens the relevance of the proposed dynamic functions. The presented analysis allows to improve the adherence of the simulated burn rate to that of literature turbulent flames, and it unfolds the innovative possibility to objectively test combustion models under any prescribed turbulence/flame interaction regime. The solid data-driven representation of turbulent combustion physics is expected to reduce the tuning effort in ICE combustion simulations, providing modelling robustness in a very critical area for virtual design of innovative combustion systems.

Three-dimensional computational fluid dynamics simulation of hydrogen engines using a turbulent flame speed closure combustion model

2012 ◽  
Vol 13 (5) ◽  
pp. 464-481 ◽  
Author(s):  
Udo Gerke ◽  
Konstantinos Boulouchos
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Three Dimensional ◽  
Flame Speed ◽  
Combustion Model ◽  
Laminar Flame Speed ◽  
Release Rates ◽  
Turbulent Flame Speed

The mixture formation and combustion process of a hydrogen direct-injection internal combustion engine is computed using a modified version of a commercial three-dimensional computational fluid dynamics code. The aim of the work is the evaluation of hydrogen laminar flame speed correlations and turbulent flame speed closures with respect to combustion of premixed and stratified mixtures at various levels of air-to-fuel equivalence ratio. Heat-release rates derived from in-cylinder pressure traces are used for the validation of the combustion simulations. A turbulent combustion model with closures for a turbulent flame speed is investigated. The value of the computed heat-release rates mainly depends on the quality of laminar burning velocities and standard of turbulence quantities provided to the combustion model. Combustion simulations performed with experimentally derived laminar flame speed data give better results than those using laminar flame speeds obtained from a kinetic scheme. However, experimental data of hydrogen laminar flame speeds found in the literature are limited regarding the range of pressures, temperatures and air-to-fuel equivalence ratios, and do not comply with the demand of high-pressure engine-relevant conditions.

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

2014 ◽  
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.

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

2013 ◽  
Vol 135 (11) ◽  
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.

scholarly journals Influence of Turbulent Scalar Mixing Physics on Premixed Flame Propagation

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
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.

Prediction of Ultra-Lean SI Engine Performance by QD-Combustion Model With an Improved Laminar Flame Speed

2020 ◽  
Author(s):  
Ratnak Sok ◽  
Jin Kusaka ◽  
Kyohei Yamaguchi
Keyword(s):  
Gasoline Engine ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Combustion Process ◽  
Combustion Characteristics ◽  
Flame Speed ◽  
Combustion Model ◽  
Lean Mixture ◽  
Turbulent Flame Speed

Abstract A quasi-dimensional (QD) simulation model is a preferred method to predict combustion in the gasoline engines with reliable results and shorter calculation time compared with multi-dimensional simulation. The combustion phenomena in spark ignition (SI) engines are highly turbulent, and at initial stage of the combustion process, turbulent flame speed highly depends on laminar burning velocity SL. A major parameter of the QD combustion model is an accurate prediction of the SL, which is unstable under low engine speed and ultra-lean mixture. This work investigates the applicability of the combustion model for evaluating the combustion characteristics of a high-tumble port gasoline engine operated under ultra-lean mixture (equivalence ratio up to ϕ = 0.5) which is out of the range of currently available SL functions initially developed for a single component fuel. In this study, the SL correlation is improved for a gasoline surrogate fuel (5 components). Predicted SL data from the conventional and improved functions are compared with experimental SL data taken from a constant-volume chamber under micro-gravity condition. The SL measurements are done at reference conditions at temperature of 300K, pressure of 0.1MPaa, and at elevated conditions whose temperature = 360K, pressure = 0.1, 0.3, and 0.5 MPaa. Results show that the conventional SL model over-predicts flame speeds under all conditions. Moreover, the model predicts negative SL at very lean (ϕ ≤ 0.3) and rich (ϕ ≥ 1.9) mixture while the revised SL is well validated with the measured data. The improved SL formula is then incorporated into the QD combustion model by a user-defined function in GT-Power simulation. The engine experimental data are taken at 1000 RPM and 2000 RPM under engine load IMEPn = 0.4–0.8 MPa (with 0.1 increment) and ϕ ranges are up to 0.5. The results shows that the simulated engine performances and combustion characteristics are well validated with the experiments within 6% accuracy by using the QD combustion model coupled with the improved SL. A sensitivity analysis of the model is also in good agreement with the experiments under cyclic variation (averaged cycle, high IMEP or stable cycle, and low IMEP or unstable cycle).

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