Article
Thermodynamics
Shikhar Mohan, Moshe Matalon
Summary: This study investigates the propagation of outwardly expanding premixed flames in turbulent media. A manifold approach is used to couple the flow and flame evolution, and a sensitivity analysis is performed to understand the early flame kernel development. The study aims to quantify the influence of turbulent flow characteristics and flame instabilities on flame morphology and burning rate, and to establish scaling laws for turbulent flame speed.
COMBUSTION AND FLAME
(2022)
Article
Thermodynamics
Ruixue Feng, Andrea Gruber, Jacqueline H. Chen, Damir M. Valiev
Summary: This study investigates the interaction between periodic shear flow and laminar premixed flame through numerical simulation, revealing that the increase in the amplitude of periodic shear flow and gas expansion ratio leads to an increase in curved flame velocity, while the effect of periodic shear wavelength on flame velocity is non-monotonic.
COMBUSTION AND FLAME
(2021)
Article
Thermodynamics
Pasquale Eduardo Lapenna, Guido Troiani, Rachele Lamioni, Francesco Creta
Summary: Theoretical considerations and experiments show that there are two extreme regimes, stability-dominated and turbulence-dominated, in the competition between Darrieus-Landau hydrodynamic instability and turbulence timescales. It is found that turbulent fluctuations hinder the large scale, cusp-like structures of DL instability, leading to a unified regime where characteristics of unstable and stable flames become indistinguishable. Residual differences are still observed in some aspects, such as the power spectral density of flame front curvature, despite reaching a unified regime based on certain global indices.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Thermodynamics
Raheel Rasool, Nilanjan Chakraborty, Markus Klein
Summary: The structure of high pressure turbulent premixed Bunsen flames has been analyzed using a new Direct Numerical Simulation database, showing that flame morphology can be characterized by the skewness and kurtosis of the probability density function profiles of mean and Gaussian curvatures.
COMBUSTION AND FLAME
(2021)
Article
Thermodynamics
Hazim Shehab, Hiroaki Watanabe, Yuki Minamoto, Ryoichi Kurose, Toshiaki Kitagawa
Summary: Three-dimensional direct numerical simulations were used to investigate the influence of turbulence-flame interactions on flame structure and morphology. The most significant fuel consumption and heat release rates were found at negatively-curved flamelets. The shape of intense reaction zones was quantified and compared to planar flames, showing complex shapes like tubes and pancakes. As turbulence level increased, the number of intense reaction zones also increased, expanding to cover more parts of the flame front.
COMBUSTION AND FLAME
(2022)
Article
Thermodynamics
Xiao Cai, Jinhua Wang, Zhijian Bian, Haoran Zhao, Zhongshan Li, Zuohua Huang
Summary: The experimental study investigates the propagation of laminar and turbulent expanding flames under Darrieus-Landau instability using stoichiometric H-2/O-2/N-2 flames in a medium-scale, fan-stirred combustion chamber. It was found that turbulence accelerates the flame propagation and induces additional wrinkles, advancing the onset of acceleration stages. The interaction between DL instability and turbulence is identified as the corrugated flamelets regime, facilitating flame propagation even in intense turbulence.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Thermodynamics
Cheng Chi, Wang Han, Dominique Thevenin
Summary: Ammonia (NH3) shows promise as a carbon-free energy carrier and can be used as a fuel in gas turbines for power generation. This study investigates the impact of molecular diffusion modeling (MDM) on turbulent premixed NH3/H2/air jet flames, focusing on flame structure, NO production, and the combined role of MDM and stretch rate. The results show that MDM has a significant influence on NO production and turbulent flame speed, while having negligible impact on major species and NO distribution. Flame curvature and strain are found to be critical factors in accurately predicting NO emission and NH3/H2/air flame propagation.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Thermodynamics
Pasquale Eduardo Lapenna, Rachele Lamioni, Francesco Creta
Summary: This work investigates intrinsic flame instabilities occurring in the propagation of a deflagration wave, with a dedicated set of direct numerical simulations and coherent literature results used to develop scaling arguments for the propagation speed of self-wrinkled flames. The observed scaling is based on the number of unstable wavelengths in a reference hydrodynamic lengthscale, and an algebraic model for the wrinkling factor is developed based on this scaling, which correctly captures flame wrinkling at sub grid level. Additionally, a strategy to incorporate the self-wrinkling model into a turbulent combustion model is discussed based on the turbulence induced cut-off concept.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Thermodynamics
Victor Coulon, Jessica Gaucherand, Victor Xing, Davide Laera, Corentin Lapeyre, Thierry Poinsot
Summary: Three turbulent premixed flames, including methane/air, ammonia-hydrogen/air, and hydrogen/air flames, were analyzed and compared using 3D Direct Numerical Simulation. The results showed that the hydrogen flame exhibited significant alteration of its local flame structure, with decreased flame length and surface area, and increased burning rates. In contrast, the methane and ammonia-hydrogen flames behaved similarly.
COMBUSTION AND FLAME
(2023)
Article
Energy & Fuels
Yuzhou Cheng, Tai Jin, Kun Luo, Zongyan Li, Haiou Wang, Jianren Fan
Summary: The combustion instability in laminar premixed flames is influenced by flame holder temperature, with different instability modes at different temperatures being affected by flame characteristics, recirculation zones, and acoustic modes. ITA modes affect combustion instability in different ways, either causing intrinsic instability or coupling with acoustic modes to create new instability modes, highlighting the importance of considering ITA modes in the analysis of combustion instability in realistic systems.
Article
Chemistry, Physical
Jun Yaguchi, Wookyung Kim, Toshio Mogi, Ritsu Dobashi
Summary: This study investigates flame acceleration and blast wave of H-2-air and H-2-O-2-N-2-Ar mixtures, focusing on the effect of volumetric expansion ratio on flame acceleration. The critical Peclet number for flame acceleration decreases with decreasing equivalence ratio and increasing expansion ratio diluted with Ar.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2021)
Article
Thermodynamics
A. N. Lipatnikov, V. A. Sabelnikov
Summary: The study analyzes DNS data from a lean, complex chemistry, hydrogen-air flame to examine three different models for evaluating mean concentrations of various species in turbulent combustion research. The best predictions are obtained by using a Probability Density Function to average species mole fractions and density directly from laminar-flame profiles. This approach proves useful for evaluating mean mole fractions of different species in turbulent flames.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Thermodynamics
Jonathan F. MacArt, Jonathan M. Wang, Pavel P. Popov, Jonathan B. Freund
Summary: The ignition of a lean hydrogen-oxygen premixture and subsequent three-dimensional expanding-flame instabilities induced by focused laser breakdown are simulated in detail. Both diffusive-thermal and hydrodynamic instabilities play a role in accelerating flame expansion, with the global Karlovitz number serving as a measure of instability development. The study emphasizes the importance of vorticity production in destabilizing the flame propagation process.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Thermodynamics
Vladimir A. Sabelnikov, Andrei N. Lipatnikov, Nikolay Nikitin, Shinnosuke Nishiki, Tatsuya Hasegawa
Summary: The study reveals the different influences of thermal expansion on turbulence and the reaction zone at different density ratios, as well as the differing effects of potential and solenoidal velocity fields on the reaction zone.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Thermodynamics
Antonio Attili, Rachele Lamioni, Lukas Berger, Konstantin Kleinheinz, Pasquale E. Lapenna, Heinz Pitsch, Francesco Creta
Summary: The study investigates the effect of pressure on the hydrodynamic stability limits of lean methane-air premixed flames using Direct Numerical Simulation. Results show that increasing pressure causes a significant decrease in the cut-off length scale, which is not solely attributed to the reduced flame thickness due to elevated pressures. This decrease is linked to the increase of the Zeldovich number with pressure, impacting the chain termination reactions and influencing the flame dynamics.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Thermodynamics
A. N. Lipatnikov, V. A. Sabelnikov, N. V. Nikitin, S. Nishiki, T. Hasegawa
Summary: The study reveals that combustion-induced thermal expansion significantly affects the flow structure, especially in the local structure of unburned reactants. This effect is amplified by the density ratio and is present not only within the mean flame brush but also upstream.
FLOW TURBULENCE AND COMBUSTION
(2021)
Article
Mechanics
V. A. Sabelnikov, A. N. Lipatnikov, S. Nishiki, H. L. Dave, F. E. Hernandez Perez, W. Song, Hong G. Im
Summary: The study discusses the potential for dilatational dissipation to exceed solenoidal dissipation in different combustion conditions, and highlights that the effect of combustion-induced thermal expansion on dissipation rates is not solely due to an increase in mixture viscosity caused by temperature rise. Additionally, the mechanisms of dilatational dissipation are examined under high Karlovitz numbers, suggesting that molecular transport of species and heat has an increasing impact on dilatation with higher Karlovitz numbers.
Article
Mechanics
Hsu Chew Lee, Peng Dai, Minping Wan, Andrei N. Lipatnikov
Summary: Unsteady three-dimensional direct numerical simulations were conducted to study the effect of molecular transport coefficients on turbulent burning velocity in lean hydrogen-air flames. The results show that the differences in transport coefficients significantly impact the burning velocity, which is controlled by Lewis number effects rather than preferential diffusion effects. This impact is more pronounced in leaner flames.
Article
Mechanics
Andrei N. Lipatnikov, Vladimir A. Sabelnikov
Summary: This study explores the influence of flame folding on the local flame structure in a turbulent flow. The results show that flame folding does not significantly affect the validity of the flamelet paradigm, as analyzed using a new diagnostic technique.
Review
Energy & Fuels
Andrei N. Lipatnikov, Vladimir A. Sabelnikov
Summary: This paper aims to overview different definitions of Karlovitz number, compare them, and suggest the most appropriate choice of Karlovitz number for each combustion regime boundary. Moreover, the influence of complex combustion chemistry on the thickness and various Karlovitz numbers and their relations is explored based on simulation results of laminar premixed flames.
Article
Chemistry, Physical
Hsu Chew Lee, Peng Dai, Minping Wan, Andrei N. Lipatnikov
Summary: This study compares the roles played by the leading and trailing edges of a premixed turbulent flame brush in its propagation by analyzing the data obtained from 16 hydrogen-air flames in intense turbulence. The analysis shows that preferential diffusion of hydrogen significantly increases the local fuel consumption and heat release rates near the leading or trailing edges of the flame brushes. Furthermore, the turbulent burning velocities computed by activating preferential diffusion for hydrogen are higher than those computed for other species, indicating the important role of the leading edge in the propagation of turbulent flames.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2022)
Article
Mechanics
Vladimir A. Sabelnikov, Andrei N. Lipatnikov, Nikolay V. Nikitin, Francisco E. Hernandez-Perez, Hong G. Im
Summary: The influence of combustion-induced thermal expansion on turbulence in unburned gas was explored through analysis of two turbulent lean hydrogen-air flames. The study found significant effects of thermal expansion on potential structure functions in unburned reactants, emphasizing the importance of advanced turbulence models in flames.
Article
Energy & Fuels
HsuChew Lee, Abouelmagd Abdelsamie, Peng Dai, Minping Wan, Andrei N. Lipatnikov
Summary: This article uses numerical simulations to study the characteristics of seven highly turbulent lean hydrogen-air flames. The results show that using the mixture-averaged model significantly increases the turbulent burning velocity, especially in lean flames. The turbulence length scale also affects the burning velocity, and the fuel consumption rate exhibits universality in different cases.
Article
Mechanics
Vladimir A. Sabelnikov, Andrei N. Lipatnikov, Nikolay V. Nikitin, Francisco E. Hernandez-Perez, Hong G. Im
Summary: This study aims to analyze and numerically explore the influence of combustion-induced thermal expansion on turbulence in premixed flames. A new criterion for assessing the importance of the thermal expansion effects is introduced, and the direct numerical simulation (DNS) data supports the theoretical study.
Article
Mechanics
H. C. Lee, P. Dai, M. Wan, A. N. Lipatnikov
Summary: Direct numerical simulation data is used to analyze the effect of molecular diffusion on flame surface density, displacement speed, and flame surface density transport equation terms in turbulent lean hydrogen-air flames. The results show that the increase in turbulent burning rates is mainly due to an increase in local fuel consumption rate, rather than an increase in flame surface area. This phenomenon is more prominent in richer flames and particularly near the flame leading edges.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
V. A. Sabelnikov, A. N. Lipatnikov, N. V. Nikitin, F. E. Hernandez Perez, H. G. Im
Summary: The direction of inter-scale transfer of scalar variance between subgrid scale (SGS) and resolved scalar fields in turbulent flames is explored. The backscatter of scalar variance from SGS to resolved scales is observed, even in highly turbulent flames. This backscatter is primarily influenced by the potential velocity perturbations generated due to dilatation in instantaneous local flames and is substantially promoted by the alignment of spatial gradient and potential-velocity contribution to the local SGS scalar flux. These findings suggest the need for the development of SGS models capable of predicting backscatter in large eddy simulations of turbulent flames.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Andrei N. Lipatnikov, Vladimir A. Sabelnikov
Summary: This study focuses on the influence of the combustion progress variable on flame and flow characteristics in a lean hydrogen-air complex chemistry flame. It is found that as the combustion progress increases, the fluctuations of local flame characteristics decrease, but the turbulence characteristics and flame-turbulence interaction do not decrease significantly. This is hypothesized to be caused by the reduction of turbulence residence time due to combustion-induced acceleration of the local flow.
Article
Thermodynamics
Andrei N. Lipatnikov
Summary: In this study, unsteady three-dimensional DNS data obtained previously by Dave et al. (2020; J Fluid Mech 884. A46) is processed to test a perfectly stirred reactor model. The results indicate that it is difficult to satisfy the constraint of Delta 0.5dL in contemporary unsteady multidimensional numerical simulations.
INTERNATIONAL JOURNAL OF ENGINE RESEARCH
(2023)
Article
Physics, Fluids & Plasmas
Jerzy Chomiak, Andrei N. Lipatnikov
Summary: By comparing the effect of strain rates on laminar flame instabilities and the strain rates generated by small-scale turbulent eddies, this study suggests a simple criterion to evaluate the importance of instabilities in increasing the premixed flame surface area in turbulent flows.