Article
Thermodynamics
Benjamin W. Keeton, Keiko K. Nomura, Antonio L. Sanchez, Forman A. Williams
Summary: Axisymmetric numerical simulations are conducted to investigate the influence of swirl on the stabilization of non-premixed jet flames. The results show that the coupling between swirl and flame propagation velocity as well as air-jet velocity affects the liftoff and blowoff of the flame, and the rotational speed of the swirl also affects the liftoff height and stability of the flame.
COMBUSTION AND FLAME
(2023)
Article
Thermodynamics
Insong Kim, Jongchol Kim, Yongmin Choe, Kumsong Ryu, Jongchol Cha, Jonghyok Ri
Summary: This study investigates the effects of twisted and straight swirler vanes on the combustion characteristics in a swirl micro-combustor, and compares them under different inlet velocities, equivalence ratios, and wall materials. The results show that increasing the vane angle expands the recirculation zones in both types of swirler. The effect of vane angle on wall temperature is different for each type.
APPLIED THERMAL ENGINEERING
(2023)
Article
Mechanics
Rigoberto Ortega-Chavez, Lian Gan, Philip H. H. Gaskell
Summary: The controlled discharge of fluid with swirl promotes the breakdown of the leading vortex ring structure, resulting in significant negative azimuthal vorticity generation. The interaction between vortex breakdown and swirl increases the radius of the primary vortex core, decreases the self-induced propagation velocity of the leading ring, and increases vortex stretching along the circular primary vortex core. These effects lead to an increased dimensionless kinetic energy for the primary ring and a decrease in the circulation based formation number, F.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
Takashi Ohta, Yuta Onishi, Yasuyuki Sakai
Summary: This study investigated the mechanism of modulation of turbulent structures near a combustion engine wall through direct numerical simulations. The results showed that flame propagation influenced the turbulence and suppressed the turbulence vortices along the wall. Additionally, the study found that the vortex structure had a significant impact on the heat release rate distribution and concentration distribution of the chemical species.
COMBUSTION AND FLAME
(2022)
Article
Thermodynamics
Jianlong Wan, Haibo Zhao
Summary: This study investigated the laminar methane-air non-premixed flame patterns in a radial microchannel under the synergistic effect of heat and flow recirculation through numerical simulations. It found that the flame remained stable until extinguished, indicating strong flame stability. Different flame patterns were observed at small, moderate, and large Reynolds numbers, providing insights into flame propagation characteristics in a radial channel.
COMBUSTION AND FLAME
(2021)
Article
Thermodynamics
S. Herff, K. Pausch, S. Loosen, W. Schroeder
Summary: The study investigates the impact of confinement on a turbulent lean premixed swirl flame using numerical simulation methods. The results show good agreement between numerical and experimental data in symmetric confined configuration, where confinement defines the recirculation zones and turbulence intensity of swirling jets.
COMBUSTION AND FLAME
(2022)
Article
Energy & Fuels
Xiao Yang, Mohan Li, Ziyong Yin, Zhengchang Song
Summary: This study investigates the impact of swirler vane angle (beta) on the combustion behavior of premixed lean hydrogen-air flame in a swirl micro-combustor through numerical simulations. The findings reveal that a beta of 15 degrees results in a larger lower flammability limit (LFL) compared to a beta of 0 degrees. Additionally, beta values of 30 degrees, 45 degrees, and 60 degrees show minimal differences in LFL, with all values being lower than that of beta = 0 degrees. The anchoring of the flame is primarily influenced by the corner recirculation zone (CRZ) at beta values of 0 degrees and 15 degrees, while at beta values exceeding 30 degrees, flame anchoring is mainly determined by the inner recirculation zone (IRZ). The stabilization ability of the IRZ is stronger than that of the CRZ, but excessive swirling intensity leads to an increase in the length of the IRZ, resulting in a decrease in stabilization ability. Increasing the beta enhances the outer wall temperature at relatively low inlet velocities; however, at larger inlet velocities, a high beta reduces the thermal performance and combustion efficiency of the combustor due to the downstream movement of the flame root and reaction zone. This research improves our understanding of swirling flame characteristics in micro-combustors and offers valuable insights for the design and optimization of swirl micro-combustors.
CHEMICAL ENGINEERING AND PROCESSING-PROCESS INTENSIFICATION
(2023)
Article
Energy & Fuels
Siqi Cai, Wenquan Yang, Yan Ding, Qinghua Zeng, Jianlong Wan
Summary: The novel micro disc-burner shows high stability and thermal output power increases with Reynolds number. The combustion characteristics are affected by the thermal conductivity of the solid wall and surface emissivity.
Article
Thermodynamics
Raghul Manosh Kumar, Ianko Chterev, Danielle Stepien, Matthew Sirignano, Benjamin L. Emerson, Christopher A. Fugger, Naibo Jiang, Sukesh Roy, Timothy C. Lieuwen
Summary: This paper analyzes the flame dynamics of lean blowoff swirl stabilized flames using simultaneous OH and CH 2 O PLIF measurements. The study quantifies extinction spots along the flame edge and entrained reactants within the combustion product region, revealing surprising findings about the behavior of the flame near blowoff. The results suggest a striking similarity between the average composition of the wake and that of a stable flame, despite significant baseflow and flame position disruption.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2021)
Article
Engineering, Aerospace
Daniel Martinez-Sanchis, Andrej Sternin, Oskar Haidn, Martin Tajmar
Summary: Direct numerical simulations are used to investigate the turbulent mixing burning of fuel-rich methane-oxygen flames in rocket engines. The results show that a significant amount of premixed combustion occurs in the non-premixed configuration, and turbulence increases the fraction of propellants burnt in oxygen-rich and near-stoichiometric conditions, influencing combustion completion at downstream positions.
Article
Nanoscience & Nanotechnology
Yupeng Gao, Xiaoguang Zhang, Wang Han, Jingxuan Li, Lijun Yang
Summary: This study investigates the effects of swirl numbers and bluff body diameters on flow structure, Reynolds stresses, and turbulent kinetic energy transport through a series of direct numerical simulations. It is found that the change in swirl number affects the inner recirculation zone and momentum transport. The presence of a bluff body contributes to the formation of the inner recirculation zone and acts as a disturbance source for the flow, promoting the formation of large-scale vortex structures.
Article
Mechanics
Yuli Cao, Ruina Xu, S. He, Peixue Jiang
Summary: This research focused on studying turbulent dynamics and heat transfer mechanisms in accelerating flows with variations in thermophysical properties and pressure drops in micron tubes. Direct numerical simulations were conducted to investigate the behavior of turbulence at supercritical pressure CO2 in heated micron tubes. The results showed that pressure drop and scale effect played important roles in the development of turbulence flows, leading to prominent property change and flow acceleration. The acceleration suppressed the production of turbulence and decreased heat transfer.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
S. Weidner, R. Hruschka, F. Leopold
Summary: Wind tunnel experiments were conducted using cylindrical models with canted fins, showing different wake flow patterns at varying fin-cant angles. The results indicated that the rotation introduced by the fins led to distinct changes in the wake flow, with higher rotation resulting in more complex flow structures.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Thermodynamics
Askar Kazbekov, Adam M. Steinberg
Summary: This paper experimentally analyzes the simultaneous influence of combustion and large-scale vortex structures on the transfer of kinetic energy across scales around the laminar flame thickness in a turbulent premixed swirl flame and a non-reacting swirl flow. The results demonstrate the importance of kinetic energy back-scatter at scales around the flame thickness and the complicated relationship between back-scatter and local flame/flow structure; these results should be considered when modeling turbulence in flames.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Thermodynamics
Lei Jiang, Gang Li, Xi Jiang, Hongbin Hu, Bo Xiao, Yanji Xu, Zhijun Lei
Summary: The lobed swirl injector showed potential in controlling combustion by switching between attached and detached flames under different conditions. The flow direction of air and fuel through the internal and external channels of the injector influence the flame behavior, while the lobed structure guides airflow.
PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY
(2021)
Article
Thermodynamics
S. Yao, A. Kronenburg, O. T. Stein
Summary: This article discusses the use of an efficient ensemble learning approach to model the filtered density function of mixture fraction in turbulent evaporating sprays. The results show that this approach achieves high accuracy comparable to a deep neural network, while significantly reducing computational requirements. It provides an alternative solution for simulating FDF statistics.
COMBUSTION AND FLAME
(2022)
Article
Engineering, Aerospace
Jiarui Zhang, Oliver T. Stein, Tien D. Luu, Ali Shamooni, Zhixun Xia, Zhenbing Luo, Likun Ma, Yunchao Feng, Andreas Kronenburg
Summary: A numerical model for aluminum cloud combustion which incorporates various physical and chemical sub-models, such as inter-phase heat transfer, phase change, heterogeneous surface reactions, homogeneous combustion, oxide cap growth, and radiation, within the Euler-Lagrange framework is proposed. The model is validated through single particle configurations and shows good agreement with empirical correlations for larger particles. The model's predictive capabilities are further evaluated by simulating aluminum/air Bunsen flames, with consistent results compared to experimental data. The proposed model provides more reasonable burning rates compared to empirical correlations in combustion stages.
CHINESE JOURNAL OF AERONAUTICS
(2022)
Article
Chemistry, Physical
W. Yang, K. K. J. Ranga Dinesh, K. H. Luo, D. Thevenin
Summary: This study investigates the combustion characteristics of ammonia and ammonia-hydrogen fuel blends under engine-relevant conditions using direct numerical simulation and detailed chemistry. The results show that adding hydrogen to ammonia improves the reactivity of the flame and enhances the combustion process.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2022)
Article
Chemistry, Physical
C. J. Ramsay, K. K. J. Ranga Dinesh
Summary: Direct gaseous fuel injection in internal combustion engines has the potential to improve combustion processes, performance, and emissions, especially in transitioning away from fossil fuels. Computational fluid dynamic studies are necessary to optimize the combustion process, and this paper presents an improved Gaseous Sphere Injection (GSI) model for more efficient and accurate investigation of direct injection gaseous fuelled engines.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2022)
Correction
Energy & Fuels
M. Rieth, A. M. Kempf, A. Kronenburg, O. T. Stein
Article
Energy & Fuels
E. J. Fraser, J. P. Le Houx, L. F. Arenas, K. K. J. Ranga Dinesh, R. G. A. Wills
Summary: A novel numerical modelling framework is developed to simulate the behavior of soluble lead flow battery with reticulated vitreous carbon (RVC) electrodes. The model is validated with experimental results. The study also presents a method to estimate the geometry of RVC electrodes with different thicknesses of electrodeposited material. The model predicts the effects of different electrolyte regions on the behavior of the battery and shows that using 100 ppi RVC electrodes can improve the voltage efficiency.
JOURNAL OF ENERGY STORAGE
(2022)
Article
Thermodynamics
Jiarui Zhang, Zhixun Xia, Likun Ma, Oliver T. Stein, Yunchao Feng, Tien D. Luu, Andreas Kronenburg
Summary: Numerical investigation of aluminum dust counterflow flames is conducted using a two-stage model that considers the effects of interphase heat transfer, phase change, heterogeneous surface reaction, oxide cap growth, homogeneous combustion, and radiation. The model is validated by comparing the results with experimental data, and the flame structure and the role of different factors in the combustion process are analyzed. The study highlights the importance of particle size, interphase heat transfer, and heterogeneous surface reaction in the flame.
COMBUSTION AND FLAME
(2022)
Article
Thermodynamics
Nadezhda Iaroslavtceva, Andreas Kronenburg, Oliver T. Stein
Summary: A novel multiple mapping conditioning (MMC) mixing time scale model has been developed for turbulent premixed combustion. It combines time scales for different combustion regimes and uses a blending function to identify zones and reduce weighting according to the Karlovitz number. DNS simulations were used to validate the model and it was found that the new mixing time scale provides accurate predictions of flame speed and flame structure across all combustion regimes.
FLOW TURBULENCE AND COMBUSTION
(2023)
Article
Chemistry, Physical
F. S. Almutairi, K. K. J. Ranga Dinesh, J. A. van Oijen
Summary: In this study, Reynolds-Averaged Navier-Stokes simulations and a novel flamelet generated manifold (FGM) hybrid combustion model were used to investigate the combustion process of a hydrogen-blended diesel-hydrogen dual-fuel engine with high hydrogen energy share. The FGM model, which incorporates preferential diffusion effects, demonstrated better predictions and accuracy for the in-cylinder characteristics compared to experimental data. The inclusion of preferential diffusion effects in the flame chemistry and transport equations successfully predicted various characteristics of the diesel-hydrogen dual-fuel combustion process.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2023)
Article
Chemistry, Physical
W. Yang, K. K. J. Ranga Dinesh, K. H. Luo, D. Thevenin
Summary: This study investigated the auto-ignition characteristics of ammonia-air and ammonia-hydrogen-air mixing layers using numerical simulations. The results showed that elevated pressure and hydrogen addition accelerated the auto-ignition process, and the heat release rate had two distinct peaks corresponding to different stages of the process. Turbulence had an impact on both stages for pure ammonia-air mixing layers, while it only affected the thermal runaway stage for ammonia-hydrogen-air mixing layers.
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
(2022)
Article
Thermodynamics
M. Sontheimer, A. Kronenburg, O. T. Stein
Summary: In this study, simulations of spray combustion in statistically homogeneous turbulence were carried out using the MMC method. The results were compared with experimental data and a dense particle method, and good agreement was observed in terms of mean and rms of reactive scalars. Although MMC predictions of mixture fraction variance were superior, both MMC and the dense particle method underpredicted conditional fluctuations. Accurate predictions of conditional mean temperature and its variance were achieved with MMC when the droplet mass was preferentially distributed to particles closest to saturation conditions. Attempts to incorporate this approach into the one-to-one coupling strategy showed some improvement but only for transitional periods. Overall, the one-to-one coupling strategy currently seems to be the most appropriate choice for two-phase coupling in MMC.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Thermodynamics
Ali Shamooni, Oliver T. Stein, Andreas Kronenburg, Andreas M. Kempf, Paulo Debiagi, Tao Li, Andreas Dreizler, Benjamin Boehm, Christian Hasse
Summary: This study investigates the influence of oxygen level and temperature on single coal particle combustion characteristics and NO X formation using fully-resolved particle simulations. The results show that higher RFG temperatures result in faster temperature and species profile peaks, while decreasing O 2 prolongs fuel release period and increases volatile combustion time. The reduction of O 2 in RFG significantly decreases NO production, while the reduction of RFG temperature has a smaller effect.
PROCEEDINGS OF THE COMBUSTION INSTITUTE
(2023)
Article
Thermodynamics
Thorsten Zirwes, Marvin Sontheimer, Feichi Zhang, Abouelmagd Abdelsamie, Francisco E. Hernandez Perez, Oliver T. Stein, Hong G. Im, Andreas Kronenburg, Henning Bockhorn
Summary: This work provides a direct comparison between OpenFOAM's built-in flow solvers and its reacting flow extension EBIdnsFoam with four other high-fidelity combustion codes, demonstrating excellent agreement in incompressible flows and more complex cases. OpenFOAM performs slower in simulating incompressible non-reacting flows compared to other codes, but achieves similar performance and excellent parallel scalability in simulating reacting flows. The results contribute to the benchmark suite for reacting flow solvers and provide a guide for achieving high numerical accuracy in OpenFOAM.
FLOW TURBULENCE AND COMBUSTION
(2023)
Article
Energy & Fuels
Dominik Meller, Linus Engelmann, Oliver T. Stein, Andreas M. Kempf
Summary: Highly-resolved Large Eddy Simulations (LES) were conducted to investigate combustion characteristics and NOx formation in swirl-induced recirculation zones of the Brigham Young University (BYU) Burner Flow Reactor (BFR). The simulations utilized the in-house LES tool PsiPhi, employing a flamelet/progress variable (FPV) approach to model the reactive multiphase flow. A reduced CRECK mechanism with 120 species and 1551 reactions, including all NOx formation mechanisms, was used. Comparisons with experimental data showed good agreement in radial profiles of major gas species. Two variants of determining NO species were explored: direct extraction from the flamelet table and solving an additional transport equation for NO. The latter approach showed superior performance in predicting NO reactions within the furnace.
