Artigos de revistas: "Flame-Spray interaction"

1

Franzelli, Benedetta, Aymeric Vié e Matthias Ihme. "Characterizing spray flame–vortex interaction: A spray spectral diagram for extinction". Combustion and Flame 163 (janeiro de 2016): 100–114. http://dx.doi.org/10.1016/j.combustflame.2015.09.006.

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Sacomano Filho, Fernando Luiz, Louis Dressler, Arash Hosseinzadeh, Amsini Sadiki e Guenther Carlos Krieger Filho. "Investigations of Evaporative Cooling and Turbulence Flame Interaction Modeling in Ethanol Turbulent Spray Combustion Using Tabulated Chemistry". Fluids 4, n.º 4 (31 de outubro de 2019): 187. http://dx.doi.org/10.3390/fluids4040187.

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Evaporative cooling effects and turbulence flame interaction are analyzed in the large eddy simulation (LES) context for an ethanol turbulent spray flame. Investigations are conducted with the artificially thickened flame (ATF) approach coupled with an extension of the mixture adaptive thickening procedure to account for variations of enthalpy. Droplets are tracked in a Euler–Lagrangian framework, in which an evaporation model accounting for the inter-phase non-equilibrium is applied. The chemistry is tabulated following the flamelet generated manifold (FGM) method. Enthalpy variations are incorporated in the resulting FGM database in a universal fashion, which is not limited to the heat losses caused by evaporative cooling effects. The relevance of the evaporative cooling is evaluated with a typically applied setting for a flame surface wrinkling model. Using one of the resulting cases from the evaporative cooling analysis as a reference, the importance of the flame wrinkling modeling is studied. Besides its novelty, the completeness of the proposed modeling strategy allows a significant contribution to the understanding of the most relevant phenomena for the turbulent spray combustion modeling.

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Innocenti, Alessandro, Antonio Andreini, Bruno Facchini e Antonio Peschiulli. "Numerical analysis of the dynamic flame response of a spray flame for aero-engine applications". International Journal of Spray and Combustion Dynamics 9, n.º 4 (16 de maio de 2017): 310–29. http://dx.doi.org/10.1177/1756827717703577.

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Incoming standards on NO x emissions are motivating many aero-engine manufacturers to adopt the lean burn combustion concept. One of the most critical issues affecting this kind of technology is the occurrence of thermo-acoustic instabilities that may compromise combustor life and integrity. Therefore the prediction of the thermo-acoustic behaviour of the system becomes of primary importance. In this paper, the complex interaction between the system acoustics and a turbulent spray flame for aero-engine applications is numerically studied. The dynamic flame response is computed exploiting reactive URANS simulations and system identification techniques. Great attention has been devoted to the impact of liquid fuel evolution and droplet dynamics. For this purpose, the GE Avio PERM (partially evaporating and rapid mixing) lean injection system has been analysed, focussing attention on the effect of several modelling parameters on the combustion and on the predicted flame response. A frequency analysis has also been set up and exploited to obtain even more insight on the dynamic flame response of the spray flame. The application is one of the few in the literature where the dynamic flame response of spray flames is numerically investigated, providing a description in terms of flame transfer function and detailed information on the physical phenomena.

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Dressler, Louis, Fernando Luiz Sacomano Filho, Florian Ries, Hendrik Nicolai, Johannes Janicka e Amsini Sadiki. "Numerical Prediction of Turbulent Spray Flame Characteristics Using the Filtered Eulerian Stochastic Field Approach Coupled to Tabulated Chemistry". Fluids 6, n.º 2 (22 de janeiro de 2021): 50. http://dx.doi.org/10.3390/fluids6020050.

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The Eulerian stochastic fields (ESF) method, which is based on the transport equation of the joint subgrid scalar probability density function, is applied to Large Eddy Simulation of a turbulent dilute spray flame. The approach is coupled with a tabulated chemistry approach to represent the subgrid turbulence–chemistry interaction. Following a two-way coupled Eulerian–Lagrangian procedure, the spray is treated as a multitude of computational parcels described in a Lagrangian manner, each representing a heap of real spray droplets. The present contribution has two objectives: First, the predictive capabilities of the modeling framework are evaluated by comparing simulation results using 8, 16, and 32 stochastic fields with available experimental data. At the same time, the results are compared to previous studies, where the artificially thickened flame (ATF) model was applied to the investigated configuration. The results suggest that the ESF method can reproduce the experimental measurements reasonably well. Comparisons with the ATF approach indicate that the ESF results better describe the flame entrainment into the cold spray core of the flame. Secondly, the dynamics of the subgrid scalar contributions are investigated and the reconstructed probability density distributions are compared to common presumed shapes qualitatively and quantitatively in the context of spray combustion. It is demonstrated that the ESF method can be a valuable tool to evaluate approaches relying on a pre-integration of the thermochemical lookup-table.

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Lackmann, Tim, Andreas Nygren, Anders Karlsson e Michael Oevermann. "Investigation of turbulence–chemistry interactions in a heavy-duty diesel engine with a representative interactive linear eddy model". International Journal of Engine Research 21, n.º 8 (5 de dezembro de 2018): 1469–79. http://dx.doi.org/10.1177/1468087418812319.

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Simulations of a heavy-duty diesel engine operated at high-load and low-load conditions were compared to each other, and experimental data in order to evaluate the influence of turbulence–chemistry interactions on heat release, pressure development, flame structure, and temperature development are quantified. A recently developed new combustion model for turbulent diffusion flames called representative interactive linear eddy model which features turbulence–chemistry interaction was compared to a well-stirred reactor model which neglects the influence of turbulent fluctuations on the mean reaction rate. All other aspects regarding the spray combustion simulation like spray break-up, chemical mechanism, and boundary conditions within the combustion chamber were kept the same in both simulations. In this article, representative interactive linear eddy model is extended with a progress variable, which enables the model to account for a flame lift-off and split injection, when it is used for diffusion combustion. In addition, the extended version of representative interactive linear eddy model offers the potential to treat partially premixed and premixed combustion as well. The well-stirred reactor model was tuned to match the experimental results, thus computed pressure and apparent heat release are in close agreement with the experimental data. Representative interactive linear eddy model was not tuned specifically for the case and thus the computed results for pressure and heat release are in reasonable agreement with experimental data. The computational results show that the interaction of the turbulent flow field and the chemistry reduce the peak temperatures and broaden up the turbulent flame structure. Since this is the first study of a real combustion engine (metal engine) with the newly developed model, representative interactive linear eddy model appears as a promising candidate for predictions of spray combustion in engines, especially in combustion regimes where turbulence–chemistry interaction plays an even more important role like, example given, in low-temperature combustion or combustion with local extinction and re-ignition.

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Zhao, Wanhui, Haiqiao Wei, Ming Jia, Zhen Lu, Kai H. Luo, Rui Chen e Lei Zhou. "Flame–spray interaction and combustion features in split-injection spray flames under diesel engine-like conditions". Combustion and Flame 210 (dezembro de 2019): 204–21. http://dx.doi.org/10.1016/j.combustflame.2019.08.031.

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Senda, J., e H. G. Fujimoto. "Multidimensional Modeling of Impinging Sprays on the Wall in Diesel Engines". Applied Mechanics Reviews 52, n.º 4 (1 de abril de 1999): 119–38. http://dx.doi.org/10.1115/1.3098930.

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This article summarizes model analysis of the dispersion process of a Diesel spray on the wall surface in order to simulate the spray-wall interaction process in Diesel engines. The mixture formation process near the wall of the piston cavity affects the combustion process and the hydrocarbon or soot formation process through the quenching of the mixture and flame at the wall surface. In particular, mixture burning occurs mainly near the cavity wall through the whole combustion period in the case of high pressure fuel injection. In this article, representative modeling approaches on spray-wall interaction process including the film flow formation are summarized briefly. Then, our models of spray impingement for low/high-temperature models including the process of fuel film formation, film breakup, wall-drop/film heat transfer, and droplet breakup owing to the solid-liquid interface boiling are introduced with the comparison of experimental results. This review article includes 83 references.

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Santoro, Vito S., Dimitrios C. Kyritsis e Alessandro Gomez. "An experimental study of vortex-flame interaction in counterflow spray diffusion flames". Proceedings of the Combustion Institute 28, n.º 1 (janeiro de 2000): 1023–30. http://dx.doi.org/10.1016/s0082-0784(00)80310-0.

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Maes, Noud, Mark Hooglugt, Nico Dam, Bart Somers e Gilles Hardy. "On the influence of wall distance and geometry for high-pressure n-dodecane spray flames in a constant-volume chamber". International Journal of Engine Research 21, n.º 2 (17 de setembro de 2019): 406–17. http://dx.doi.org/10.1177/1468087419875242.

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To isolate the effect of flame–wall interaction from representative operating conditions of an internal combustion engine, experiments were performed in a constant-volume pre-burn vessel. Three different wall geometries were studied at distances of 32.8, 38.2, and 46.2 mm from a single-hole 0.09-mm orifice diameter fuel injector. A flat wall provides a simplified case of flame–wall interaction. To mimic the division of a jet into two regions by the piston bowl rim in an engine, a two-dimensional confined wall is used. A third, axisymmetric confined wall geometry allows a second simplified comparison to numerical simulations in a Reynolds-averaged Navier–Stokes framework. As a limiting situation for a free jet, the distance from the injector orifice to the end wall of the chamber is 95 mm. Thermocouples installed in the end wall provided insights into local heat losses for reference cases without a wall insert. The test conditions were according to the Engine Combustion Network Spray A guidelines with an ambient temperature of 900 K and an ambient density of 22.8 kg/m3 with 15% O2. Flame structures were studied using high-speed OH* chemiluminescence with integrated single-shot OH PLIF and combined with pressure-based apparent heat release data to infer combustion progress and spray behavior. Soot was studied in a qualitative manner using high-speed natural luminosity imaging with integrated high-speed laser-induced incandescence. Overall, increased mixing upon interaction with the surfaces is observed to increase early heat release rate and to significantly reduce soot, with the nearest wall distance showing most effect. The flat wall gives rise to the most significant effects in all cases.

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Venturi, F., e T. Hussain. "Radial Injection in Suspension High Velocity Oxy-Fuel (S-HVOF) Thermal Spray of Graphene Nanoplatelets for Tribology". Journal of Thermal Spray Technology 29, n.º 1-2 (14 de novembro de 2019): 255–69. http://dx.doi.org/10.1007/s11666-019-00957-y.

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AbstractFriction is a major issue in energy efficiency of any apparatus composed of moving mechanical parts, affecting durability and reliability. Graphene nanoplatelets (GNPs) are good candidates for reducing friction and wear, and suspension high velocity oxy-fuel (SHVOF) thermal spray is a promising technique for their scalable and fast deposition, but it can expose them to excessive heat. In this work, we explore radial injection of GNPs in SHVOF thermal spray as a means of reducing their interaction with the hot flame while still allowing a high momentum transfer and effective deposition. Feedstock injection parameters, such as flowrate, injection angle and position, were studied using high-speed imaging and particles temperature and velocity monitoring at different flame powers using Accuraspray 4.0. Unlubricated ball-on-flat sliding wear tests against an alumina counterbody ball showed a friction coefficient reduction up to a factor 10 compared to the bare substrate, down to 0.07. The deposited layer of GNPs protects the underlying substrate by allowing low-friction dry sliding. A transmission electron microscopy study showed GNPs preserved crystallinity after spray and became amorphized and wrinkled upon wear. This study focused on GNPs but could be relevant to other heat- and oxidation-sensitive materials such as polymers, nitrides and 2D materials.

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Jiang, Tsung Leo, e Huei-Huang Chiu. "Combustion of a Fuel Droplet Surrounded by Oxidizer Droplets". Journal of Heat Transfer 113, n.º 4 (1 de novembro de 1991): 959–65. http://dx.doi.org/10.1115/1.2911228.

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The interaction between a burning fuel droplet and satellite oxidizer droplets is studied analytically. The effects of droplet spacing and droplet size ratio on the flame configuration of a burning fuel droplet with a satellite oxidizer droplet are analyzed in a high-temperature oxidizing environment by using the bispherical coordinate system. Three combustion modes including normal combustion, conjugate combustion, and composite combustion are identified at appropriate droplet size ratio and droplet spacing. The burning rate of the fuel droplet is found to be greater than that of an isolated burning fuel droplet, and to increase with the decreasing distance between two droplets. This result has shown a positive effect on the interaction between fuel and oxidizer droplets, in contrast to that of two interacting fuel droplets where the burning rate decreases with decreasing droplet spacing. The combustion configuration of a fuel droplet surrounded by six satellite oxidizer droplets symmetrically is also examined by the method of images. The flame that encloses the fuel droplet is found to be “compressed” and distorted to a nonspherical shape due not only to the group effect among oxidizer droplets but also to the interaction of bipropellant droplets. The results indicate that the burning rate of a fuel droplet increases and the flame size decreases significantly as a result of an increased supply of oxidizer vapor provided by the surrounding oxidizer droplets. Therefore properly optimized bipropellant combustion is potentially able to achieve a desired combustion performance with a much smaller combustor than a conventional spray burner.

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Conte, Francesco, Serena Esposito, Vladimiro Dal Santo, Alessandro Di Michele, Gianguido Ramis e Ilenia Rossetti. "Flame Pyrolysis Synthesis of Mixed Oxides for Glycerol Steam Reforming". Materials 14, n.º 3 (31 de janeiro de 2021): 652. http://dx.doi.org/10.3390/ma14030652.

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Flame spray pyrolysis was used to produce nanosized Ni-based catalysts starting from different mixed oxides. LaNiO3 and CeNiO3 were used as base materials and the formulation was varied by mixing them or incorporating variable amounts of ZrO2 or SrO during the synthesis. The catalysts were tested for the steam reforming of glycerol. One of the key problems for this application is the resistance to deactivation by sintering and coking, which may be increased by (1) improving Ni dispersion through the production of a Ni-La or Ni-Ce mixed oxide precursor, and then reduced; (2) using an oxide as ZrO2, which established a strong interaction with Ni and possesses high thermal resistance; (3) decreasing the surface acidity of ZrO2 through a basic promoter/support, such as La2O3; and (4) adding a promoter/support with very high oxygen mobility such as CeO2. A further key feature is the use of a high temperature synthesis, such as flame spray pyrolysis, to improve the overall thermal resistance of the oxides. These strategies proved effective to obtain active and stable catalysts at least for 20 h on stream with very limited coke formation.

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Shinjo, J., e A. Umemura. "Droplet/turbulence interaction and early flame kernel development in an autoigniting realistic dense spray". Proceedings of the Combustion Institute 34, n.º 1 (janeiro de 2013): 1553–60. http://dx.doi.org/10.1016/j.proci.2012.05.074.

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Tianshui, Liang, Liu Mengjie, Wei Xinli e Zhong Wei. "An Experimental Study on the Interaction of Water Mist with Vertical/Horizontal Spray Flame". Procedia Engineering 84 (2014): 543–52. http://dx.doi.org/10.1016/j.proeng.2014.10.466.

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Gehre, Patrick, Anne Schmidt, Steffen Dudczig, Jana Hubálková, Christos G. Aneziris, Nick Child, Ian Delaney, Gilbert Rancoule e Duane DeBastiani. "Interaction of slip- and flame-spray coated carbon-bonded alumina filters with steel melts". Journal of the American Ceramic Society 101, n.º 7 (24 de janeiro de 2018): 3222–33. http://dx.doi.org/10.1111/jace.15431.

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Hulkkonen, Tuomo, Aki Tilli, Ossi Kaario, Olli Ranta, Teemu Sarjovaara, Ville Vuorinen, Martti Larmi e Kalle Lehto. "Late post-injection of biofuel blends in an optical diesel engine: Experimental and theoretical discussion on the inevitable wall-wetting effects on oil dilution". International Journal of Engine Research 18, n.º 7 (17 de agosto de 2016): 645–56. http://dx.doi.org/10.1177/1468087416663548.

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In a diesel engine, diesel particulate filter is used to reduce particle matter emissions. Diesel particulate filter requires periodic regenerations under high-temperature conditions in the exhaust pipe in order to oxidize the accumulated soot. A common strategy to produce high exhaust gas temperature is to inject late post-injections after the main injection. However, this practice may dilute the engine oil, causing engine wear. Biofuel addition to petroleum diesel may increase oil dilution even more. This is related to the fuel spray characteristics, the post-injection control and the vaporization process of fuel in engine oil. In this study, spray properties of late post-injection were studied with petroleum diesel and two types of transport biofuel blends containing 30% either fatty acid methyl ester or hydro-treated vegetable oil. Three different late post-injection timings were investigated. Image sequences of the main spray flame as well as the non-combusting late post-injection spray were extracted. In order to verify oil dilution during regeneration cycle and late post-injection, oil samples from six-cylinder test engine were analyzed. According to the present experiments, differences in the spray characteristics are not significant with the tested fuels. However, higher oil dilution rates were observed with fuel blend composed of 30% fatty acid methyl ester. All the studied late post-injection timings were noted to lead to the unwanted cylinder spray/wall interaction and wall-wetting consequently diluting the engine oil. The spray/wall interaction is thoroughly explained by introducing a theoretical/computational framework which characterizes any spray/wall interaction in terms of a phase diagram for any considered operation conditions. The novelty of this study arises from (1) first comparison of fatty acid methyl ester and hydro-treated vegetable oil blends in an optical engine, (2) strong evidence on the phenomena related to post-injection phase in six-cylinder and single-cylinder optical engine configurations and (3) the development of a single-droplet model showing inevitable wall-wetting.

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Tong, Xin, Jiafeng Yu, Ling Zhang e Jian Sun. "Fabrication of Stable Cu-Ce Catalyst with Active Interfacial Sites for NOx Elimination by Flame Spray Pyrolysis". Catalysts 12, n.º 4 (11 de abril de 2022): 432. http://dx.doi.org/10.3390/catal12040432.

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The complete conversion of NOx to harmless N2 without N2O formation is crucial for the control of air pollution, especially at low temperatures. Cu-based catalysts are promising materials due to their low cost and high activity in NO dissociation, even comparable to noble metals; however, they suffer from low stability. Here, we established a Cu-Ce catalyst in one step with strong metal–support interaction by the flame spray pyrolysis (FSP) method. Almost 100% NO conversion was achieved at 100 °C, and they completely transferred into N2 at a low temperature (200 °C) for the FSP-CuCe catalyst, exhibiting excellent performance in NO reduction by CO reaction. Moreover, the catalytic performance can stay stable, while 23% NO conversion was lost in the same condition for the one made by the co-precipitation (CP) method. This can be attributed to the synergistic effect of abundant active interfacial sites and more flexible surface oxygen created during the FSP process. The flame technology developed here provides an efficient way to fabricate strong metal–support interactions, exhibiting notable potential in the design of stable Cu-based catalysts.

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Han, Karam, Jaeyeob Seo e Kang Y. Huh. "Lagrangian conditional moment closure model with flame group interaction for lifted turbulent spray jet flames". Combustion Theory and Modelling 21, n.º 3 (24 de outubro de 2016): 419–39. http://dx.doi.org/10.1080/13647830.2016.1242780.

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Khalid, Amir, M. Jaat, Izzuddin Zaman, B. Manshoor e Mas Fawzi. "Effect of Pilot Injection on Mixture Formation, Ignition Process and Flame Development in Diesel Combustion". Applied Mechanics and Materials 390 (agosto de 2013): 327–32. http://dx.doi.org/10.4028/www.scientific.net/amm.390.327.

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The alternative combustion strategies with systematic control of mixture formation have provided new opportunities and considerable improvement in the combustion process and response to meet the stringent emissions standards. Purpose of this research is to investigate the influences of pilot injection on the fuel-air premixing especially during ignition delay period. During this period, the interaction between fuel spray and surrounding gas prior to ignition which linked to the improvement of mixture formation, ignition process and initial heat recovery thus predominantly influences the combustion process and exhaust emissions. This study investigates the effects of pilot injection using a rapid compression machine together with the schlieren photography and direct photography methods. The detail behavior of mixture formation during ignition delay period was investigated using the schlieren photography system with a high speed digital video camera. This method can capture spray evaporation, spray interference and mixture formation clearly with real images. Ignition process and flame development were investigated by direct photography method using a light sensitive high-speed color digital video camera. Pilot injection promotes mixture formation during ignition delay period and slower oxidation reaction and thus leads to earlier rise and lower peak heat release rate.

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Ozel Erol, Gulcan, e Nilanjan Chakraborty. "Effects of Mean Inflow Velocity and Droplet Diameter on the Propagation of Turbulent V-Shaped Flames in Droplet-Laden Mixtures". Fluids 6, n.º 1 (22 de dezembro de 2020): 1. http://dx.doi.org/10.3390/fluids6010001.

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Three-dimensional carrier phase Direct Numerical Simulations of V-shaped n-heptane spray flames have been performed for different initially mono-sized droplet diameters to investigate the influence of mean flow velocity on the burning rate and flame structure at different axial locations from the flame holder. The fuel is supplied as liquid droplets through the inlet and an overall (i.e., liquid + gaseous) equivalence ratio of unity is retained in the unburned gas. Additionally, turbulent premixed stoichiometric V-shaped n-heptane flames under the same turbulent flow conditions have been simulated to distinguish the differences in combustion behaviour of the pure gaseous phase premixed combustion in comparison to the corresponding behaviour in the presence of liquid n-heptane droplets. It has been found that reacting gaseous mixture burns predominantly under fuel-lean mode and the availability of having fuel-lean mixture increases with increasing mean flow velocity. The extent of flame wrinkling for droplet cases has been found to be greater than the corresponding gaseous premixed flames due to flame-droplet-interaction, which is manifested by dimples on the flame surface, and this trend strengthens with increasing droplet diameter. As the residence time of the droplets within the flame decreases with increasing mean inflow velocity, the droplets can survive for larger axial distances before the completion of their evaporation for the cases with higher mean inflow velocity and this leads to greater extents of flame-droplet interaction and droplet-induced flame wrinkling. Mean inflow velocity, droplet diameter and the axial distance affect the flame brush thickness. The flame brush thickens with increasing droplet diameter for the cases with higher mean inflow velocity due to the predominance of fuel-lean gaseous mixture within the flame. However, an opposite behaviour has been observed for the cases with lower mean inflow velocity where the smaller extent of flame wrinkling due to smaller values of integral length scale to flame thickness ratio arising from higher likelihood of fuel-lean combustion for larger droplets dominates over the thickening of the flame front. It has been found that the major part of the heat release arises due to premixed mode of combustion for all cases but the contribution of non-premixed mode of combustion to the total heat release has been found to increase with increasing mean inflow velocity and droplet diameter. The increase in the mean inflow velocity yields an increase in the mean values of consumption and density-weighted displacement speed for the droplet cases but leads to a decrease in turbulent burning velocity. By contrast, an increase in droplet diameter gives rise to decreases in turbulent burning velocity, and the mean values of consumption and density-weighted displacement speeds. Detailed physical explanations have been provided to explain the observed mean inflow velocity and droplet diameter dependences of the flame propagation behaviour.

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Raut, Ankit A., e J. M. Mallikarjuna. "Effects of direct water injection and injector configurations on performance and emission characteristics of a gasoline direct injection engine: A computational fluid dynamics analysis". International Journal of Engine Research 21, n.º 8 (2 de dezembro de 2019): 1520–40. http://dx.doi.org/10.1177/1468087419890418.

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In-cylinder water injection is a promising approach for reducing NOx and soot emissions from internal combustion engines. It allows one to use a higher compression ratio by reducing engine knock; hence, higher fuel economy and power output can be achieved. However, water injection can also affect engine combustion and emission characteristics if water injection and injector parameters are not properly set. Majority of the previous studies on the water injection are done through experiments. Therefore, subtle aspects of water injection such as in-cylinder interaction of water sprays, spatial distribution of water vapor, and effect on flame propagation are not clearly understood and rarely reported in literature due to experimental limitations. Thus, in the present article, a computational fluid dynamics investigation is carried out to analyze the effects of direct water injection under various injector configurations on water evaporation, combustion, performance, and emission characteristics of a gasoline direct injection engine. The emphasis is given to analyze in-cylinder water spray interactions, flame propagation, water spray droplet size distribution, and water vapor spatial distribution inside the engine cylinder. For the study, the water-to-fuel ratio is varied from 0 to 1. Various water injector configurations using nozzle hole diameters of 0.14, 0.179, and 0.205 mm, along with nozzle holes of 4, 5, 6, and 7, are considered for comparison in addition to the case of no_water. Computational fluid dynamics models used in this study are validated with the available data in literature. From the results, it is found that the emission and performance characteristics of the engine are highly dependent on water evaporation characteristics. Also, the water-to-fuel ratio of 0.6 with 6 number of nozzle holes and the nozzle diameter of 0.14 mm results in the highest indicated mean effective pressure and the lowest NOx, soot, and CO emissions compared to other cases considered.

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Friedman, J., M. Renksizbulut e A. Zaheer. "THE INTERACTION OF AN ANNULAR AIR JET WITH A METHANOL SPRAY FLAME IN A CYLINDRICAL COMBUSTION CHAMBER". Transactions of the Canadian Society for Mechanical Engineering 28, n.º 3-4 (setembro de 2004): 593–602. http://dx.doi.org/10.1139/tcsme-2004-0040.

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Winklhofer, E., B. Ahmadi-Befrui, B. Wiesler e G. Cresnoverh. "The Influence of Injection Rate Shaping on Diesel Fuel Sprays—An Experimental Study". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 206, n.º 3 (julho de 1992): 173–83. http://dx.doi.org/10.1243/pime_proc_1992_206_176_02.

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A current strategy in the development of direct injection (DI) diesel engine combustion systems is the control and limitation of the initial ‘premixed’ combustion heat release ensuing from the auto-ignition of the injected fuel. This requires control of the amount of fuel vaporization and mixing taking place during the ignition delay time. Since the latter is determined by the fuel composition and the in-cylinder gas temperature, development efforts have focused on the injection of well-controlled, portioned fuel quantities prior to the ignition as a means of achieving the desired goal. This practice is becoming known as ‘fuel rate shaping’. Consequently, the fuel spray penetration during this period, fuel evaporation and mixture preparation, as well as the influence of in-cylinder air motion on mixture distribution, are main subjects of interest in affording insight into fuel rate shaping attempts. These have been addressed through a combined experimental and theoretical investigation of the spray characteristics associated with different injection practices. The experimental investigations have been performed in an optically accessed spray research engine. Basic aspects of fuel spray tip penetration, time and location of auto-ignition and flame propagation have been recorded with a high-speed line-scan camera. The results provide the space and time-scale characteristics for the propagation, ignition and combustion of a selection of diesel fuel sprays. Investigations have been carried out for a conventional fuel injection system equipped with a set of different single-hole injector nozzles, as well as for a dual-spring injector and an injector with a split injection device. The experimental results provide an insight into the propagation of the fuel spray front, yield qualitative information about its spatial and temporal distribution, and, in the case of split injection, show the interaction of the initial pilot fuel portion with the main injection.

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Lucchini, Tommaso, Daniel Pontoni, Gianluca D’Errico e Bart Somers. "Modeling diesel combustion with tabulated kinetics and different flame structure assumptions based on flamelet approach". International Journal of Engine Research 21, n.º 1 (16 de julho de 2019): 89–100. http://dx.doi.org/10.1177/1468087419862945.

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Computational fluid dynamics analysis represents a useful approach to design and develop new engine concepts and investigate advanced combustion modes. Large chemical mechanisms are required for a correct description of the combustion process, especially for the prediction of pollutant emissions. Tabulated chemistry models allow to reduce significantly the computational cost, maintaining a good accuracy. In the present work, an investigation of tabulated approaches, based on flamelet assumptions, is carried out to simulate turbulent Diesel combustion in the Spray A framework. The Approximated Diffusion Flamelet is tested under different ambient conditions and compared with Flamelet Generated Manifold, and both models are validated with Engine Combustion Network experimental data. Flame structure, combustion process and soot formation were analyzed in this work. Computed results confirm the impact of the turbulent–chemistry interaction on the ignition event. Therefore, a new look-up table concept Five-Dimensional-Flamelet Generated Manifold, that accounts for an additional dimension (strain rate), has been developed and tested, giving promising results.

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Zhao, Feng, Shuangde Li, Xiaofeng Wu, Renliang Yue, Weiman Li, Xicuo Zha, Yuzhou Deng e Yunfa Chen. "Catalytic Behaviour of Flame-Made CuO-CeO2 Nanocatalysts in Efficient CO Oxidation". Catalysts 9, n.º 3 (13 de março de 2019): 256. http://dx.doi.org/10.3390/catal9030256.

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CuO-CeO2 nanocatalysts with varying CuO contents (1, 5, 9, 14 and 17 wt %) were prepared by one-step flame spray pyrolysis (FSP) and applied to CO oxidation. The inﬂuences of CuO content on the as-prepared catalysts were systematically characterized by X-ray diﬀraction (XRD), N2 adsorption-desorption at −196 °C, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen-temperature programmed reduction (H2-TPR). A superior CO oxidation activity was observed for the 14 wt % CuO-CeO2 catalyst, with 90% CO conversion at 98 °C at space velocity (60,000 mL × g−1 × h−1), which was attributed to abundant surface defects (lattice distortion, Ce3+, and oxygen vacancies) and high reducibility supported by strong synergistic interaction. In addition, the catalyst also displayed excellent stability and resistance to water vapor. Significantly, in situ diﬀuse reﬂectance infrared Fourier transform spectroscopy (in situ DRIFTS) showed that in the CO catalytic oxidation process, the strong synergistic interaction led readily to dehydroxylation and CO adsorption on Cu+ at low temperature. Furthermore, in the feed of water vapor, although there was an adverse effect on the access of CO adsorption, there was also a positive effect on the formation of fewer carbon intermediates. All these results showed the potential of highly active and water vapor-resistive CuO-CeO2 catalysts prepared by FSP.

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Ong, Jiun Cai, Kar Mun Pang, Mehdi Jangi, Xue-Song Bai e Jens Honore Walther. "Numerical Study of the Influence of Turbulence–Chemistry Interaction on URANS Simulations of Diesel Spray Flame Structures under Marine Engine-like Conditions". Energy & Fuels 35, n.º 14 (24 de junho de 2021): 11457–67. http://dx.doi.org/10.1021/acs.energyfuels.1c01091.

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Roque, Anthony, Fabrice Foucher, Quentin Lamiel, Bill Imoehl, Nicolas Lamarque e Jerome Helie. "Impact of gasoline direct injection fuel films on exhaust soot production in a model experiment". International Journal of Engine Research 21, n.º 2 (7 de outubro de 2019): 367–90. http://dx.doi.org/10.1177/1468087419879851.

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The fuel films that can be generated during the injection process in gasoline direct injection engines are the most important factor in carbon particle mass and number. They also have an influence on combustion chamber and injector tip deposits. A model experiment was set up to study a liquid film, its evaporation, and combustion with soot generation on a metal plate in realistic engine conditions. The experiment was conducted in a dedicated constant volume vessel. A liquid fuel injection system (with injection pressures up to 100 bar) directs the spray onto a plate with a controlled temperature in the range of 80 °C–200 °C. The resulting liquid film and vaporization process were studied when subjected to interaction with a laminar spherical flame. A blend of four components was used as a gasoline surrogate. The liquid film spreading, thickness, and evaporation rates were initially measured in ambient conditions. Mie scattering and schlieren measurements in the chamber conditions returned a qualitative correlation of the vaporized area with the surface temperature. Fluorescence of the light and heavy fuel components was used to quantify the influence of the vaporization process on soot production. Simultaneous measurements of natural luminosity and KL factor were analyzed to understand the process of soot production. The results showed a critical wall temperature of 120 °C at which the maximum quantity of soot is generated, which can be due to the quantity and composition of fuel film in interaction with the entrainment flows generated during combustion.

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Van Everbroeck, Tim, Aggeliki Papavasiliou, Radu-George Ciocarlan, Evangelos Poulakis, Constantine J. Philippopoulos, Erika O. Jardim, Joaquin Silvestre-Albero, Elias Sakellis, Pegie Cool e Fotios K. Katsaros. "Towards Highly Loaded and Finely Dispersed CuO Catalysts via ADP: Effect of the Alumina Support". Catalysts 12, n.º 6 (8 de junho de 2022): 628. http://dx.doi.org/10.3390/catal12060628.

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To meet current economic demands enforcing the replacement of platinum-group metals, extensively used in three-way-catalytic converters (TWC), research is driven towards low-cost and widely available base metals. However, to cope with their lower activity, high metal loadings must be coupled with increased dispersion. Herein, a series of CuO/Al2O3 samples is produced and the effect of different alumina supports’ properties on CuO dispersion, speciation and eventually on the TWC performance is studied. The alumina samples are synthesized via different methods, including soft-templating routes and flame spray pyrolysis, and compared with a commercial one, while CuO used as the catalytic active phase is added through ammonia-driven deposition–precipitation. As found, the large surface area and low crystallinity of the aluminas produced by soft-templating routes favor strong metal–support interaction, generating highly dispersed and strongly bonded CuO species at low loading and copper-aluminate phases at high loading. Notably, the use of amorphous mesoporous alumina completely prevents the formation of crystalline CuO even at 15 wt% Cu. Such high metal loading and dispersion capacity without the application of elevated calcination temperatures is one of the best reported for nonreducible supports. Catalytic evaluation of this material reveals a pronounced enhancement of oxidation activity with metal loading increase.

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Tommasi, Matteo, Davide Ceriotti, Alice Gramegna, Simge Naz Degerli, Gianguido Ramis e Ilenia Rossetti. "Oxidative Steam Reforming of Methanol over Cu-Based Catalysts". Catalysts 14, n.º 11 (28 de outubro de 2024): 759. http://dx.doi.org/10.3390/catal14110759.

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Several Cu and Ni-based catalysts were synthetized over Ce-based supports, either pure or mixed with different amounts of alumina (1:2 and 1:3 mol/mol). Different metal loadings (10–40 wt%) and preparation methods (wet impregnation, co-precipitation, and flame-spray pyrolysis—FSP) were compared for the oxidative steam reforming of methanol. Characterization of the catalysts has been performed, e.g., through XRD, BET, XPS, TPR, SEM, and EDX analyses. All the catalysts have been tested in a bench-scale continuous setup. The hydrogen yield and methanol conversion obtained have been correlated with the operating conditions, metal content, crystallinity of the catalyst particles, total surface area, and with the interaction of the metal with the support. A Cu loading of 20% wt/wt was optimal, while the presence of alumina was not beneficial, decreasing catalyst activity at low temperatures compared with catalysts supported on pure CeO2. Ni-based catalysts were a possible alternative, but the activity towards the methanation reaction at relatively high temperatures decreased inevitably the hydrogen yield. Durability and deactivation tests showed that the best-performing catalyst, 20% wt. Cu/CeO2 prepared through coprecipitation was stable for a long period of time. Full methanol conversion was achieved at 280 °C, and the highest yield of H2 was ca. 80% at 340 °C, higher than the literature data.

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30

Malkeson, S. P., U. Ahmed, A. L. Pillai, N. Chakraborty e R. Kurose. "Flame self-interactions in an open turbulent jet spray flame". Physics of Fluids 33, n.º 3 (1 de março de 2021): 035114. http://dx.doi.org/10.1063/5.0039155.

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Pera, C., e J. Reveillon. "Direct numerical simulation of spray flame/acoustic interactions". Proceedings of the Combustion Institute 31, n.º 2 (janeiro de 2007): 2283–90. http://dx.doi.org/10.1016/j.proci.2006.07.153.

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Özdemir, İ. Bedii, e Cengizhan Cengiz. "Use of Modified Temperature-Composition PDF Formulation in Modeling of Flame Dynamics in Diesel Engine Combustion". International Journal of Nonlinear Sciences and Numerical Simulation 19, n.º 6 (25 de setembro de 2018): 643–67. http://dx.doi.org/10.1515/ijnsns-2018-0023.

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AbstractIn the present work, the modified temperature-composition (MT-C) PDF formulation was embedded in the KIVA to study the characteristics of flame development and emissions in a diesel engine. The model uses a time scale defined by an energy balance on the flame surface and a new normalization scheme exploiting the maximum attainable mass fractions of progress variables. Development of the latter in the {\rm{T}} - {{\xi }} parameter space regulates the flame progress in the physical space and, thus, the approach presents some potential to capture the local flame extinction. The interactions of the swirl and spray penetration and their influence in the mixing process, combustion and emissions are also evaluated. Analyses of the temporal evolution of mixture fraction and temperature show that the swirl motion forms a homogeneous mixture on the lee sides of the spray jets where the ignition actually starts. Since the local time scales are considered in the model, the chemistry-controlled premixed combustion developing there is well predicted.

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Piatkowski, M., M. Taradaichenko e I. Zbicinski. "Energy Consumption and Product Quality Interactions in Flame Spray Drying". Drying Technology 33, n.º 9 (27 de maio de 2014): 1022–28. http://dx.doi.org/10.1080/07373937.2014.924137.

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Patel, Nayan, e Suresh Menon. "Simulation of spray–turbulence–flame interactions in a lean direct injection combustor". Combustion and Flame 153, n.º 1-2 (abril de 2008): 228–57. http://dx.doi.org/10.1016/j.combustflame.2007.09.011.

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Desantes, Jose M., Jose M. Garcia-Oliver, Ricardo Novella e Leonardo Pachano. "A numerical study of the effect of nozzle diameter on diesel combustion ignition and flame stabilization". International Journal of Engine Research 21, n.º 1 (19 de julho de 2019): 101–21. http://dx.doi.org/10.1177/1468087419864203.

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The role of nozzle diameter on diesel combustion is studied by performing computational fluid dynamics calculations of Spray A and Spray D from the Engine Combustion Network. These are well-characterized single-hole sprays in a quiescent environment chamber with thermodynamic conditions representative of modern diesel engines. First, the inert spray evolution is described with the inclusion of the concept of mixing trajectories and local residence time into the analysis. Such concepts enable the quantification of the mixing rate, showing that it decreases with the increase in nozzle diameter. In a second step, the reacting spray evolution is studied focusing on the local heat release rate distribution during the auto-ignition sequence and the quasi-steady state. The capability of a well-mixed-based and a flamelet-based combustion model to predict diesel combustion is also assessed. On one hand, results show that turbulence–chemistry interaction has a profound effect on the description of the reacting spray evolution. On the other hand, the mixing rate, characterized in terms of the local residence time, drives the main changes introduced by the increase of the nozzle diameter when comparing Spray A and Spray D.

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Raju, M. S., e W. A. Sirignano. "Spray Computations in a Centerbody Combustor". Journal of Engineering for Gas Turbines and Power 111, n.º 4 (1 de outubro de 1989): 710–18. http://dx.doi.org/10.1115/1.3240317.

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A hybrid Eulerian–Lagrangian method is employed to model the reactive flow field of a centerbody combustor. The unsteady two-dimensional gas-phase equations are represented in Eulerian coordinates and liquid-phase equations are formulated in Lagrangian coordinates. The gas-phase equations based on the conservation of mass, momentum, and energy are supplemented by turbulence and combustion models. The vaporization model takes into account the transient effects associated with the droplet heating and liquid-phase internal circulation. The integration scheme is based on the TEACH algorithm for gas-phase equations, the Runge-Kutta method for liquid-phase equations, and linear interpolation between the two coordinate systems. The calculations show that the droplet penetration and recirculation characteristics are strongly influenced by the gas- and liquid-phase interaction in such a way that most of the vaporization process is confined to the wake region of the centerbody, thereby improving the flame stabilization properties of the flow field.

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37

Franzelli, Benedetta, Philippe Scouflaire e Nasser Darabiha. "Using In Situ Measurements to Experimentally Characterize TiO2 Nanoparticle Synthesis in a Turbulent Isopropyl Alcohol Flame". Materials 14, n.º 22 (22 de novembro de 2021): 7083. http://dx.doi.org/10.3390/ma14227083.

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The objective of the present work is to show the potential of in situ measurements for the investigation of nanoparticles production in turbulent spray flames. This is achieved by considering multiple diagnostics to characterize the liquid break-up, the reactive flow and the particles production in a spray burner for TiO2 nanoparticle synthesis. The considered liquid fuel is a solution of isopropyl alcohol and titanium tetraisopropoxide (TTIP) precursor. Measurements show that shadowgraphy can be used to simultaneously localize spray and nanoparticles, light scattering allows to characterize the TiO2 nanoparticles distribution in the flame central plane, and spontaneous CH* and OH* chemiluminescences, as well as global light emission results, can be used to visualize the reactive flow patterns that may differ with and without injection of TTIP. Concerning the liquid, it is observed that it is localized in a small region close to the injector nozzle where it is dispersed by the oxygen flow resulting in droplets. The liquid droplets rapidly evaporate and TTIP is quasi-immediately converted to TiO2 nanoparticles. Finally, results show high interactions between nanoparticles and the turbulent eddies.

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Fossi, Alain, Alain DeChamplain e Benjamin Akih-Kumgeh. "Unsteady RANS and scale adaptive simulations of a turbulent spray flame in a swirled-stabilized gas turbine model combustor using tabulated chemistry". International Journal of Numerical Methods for Heat & Fluid Flow 25, n.º 5 (1 de junho de 2015): 1064–88. http://dx.doi.org/10.1108/hff-09-2014-0272.

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Purpose – The purpose of this paper is to numerically investigate the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor using the commercial computational fluid dynamic (CFD) software ANSYS FLUENT. The first scope of the study aims to explicitly compare the predictive capabilities of two turbulence models namely Unsteady Reynolds Averaged Navier-Stokes and Scale Adaptive Simulation for a reasonable trade-off between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium(NEQ) effects caused by turbulent strain such as flame stretching. Design/methodology/approach – Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases, respectively. The computing method includes a two-way coupling in which phase properties and spray source terms are interchanging between the two phases within each coupling time step. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane+toluene) are used as jet-A1 surrogates. The combustion model is based on the mean mixture fraction and its variance, and a presumed-probability density function is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the equilibrium (EQ) assumption and thereafter, detailed NEQ calculations through the steady flamelets concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1,045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0 using a sensitivity based method, Alternate Species Elimination. Findings – Numerical results of the gas velocity, the gas temperature and the species molar fractions are compared with their experimental counterparts obtained from a steady state flame available in the literature. It is observed that, SAS coupled to the tabulated flamelet-based chemistry, predicts reasonably the main flame trends, while URANS even provided with the same combustion model and computing resources, leads to a poor prediction of the global flame trends, emphasizing the asset of a proper resolution when simulating spray flames. Research limitations/implications – The steady flamelet model even coupled with a robust turbulence model does not reproduce accurately the trend of species with slow oxidation kinetics such as CO and H2, because of the restrictiveness of the solutions space of flamelet equations and the assumption of unity Lewis for all species. Practical implications – This work is adding a contribution for spray flame modeling and can be seen as an extension to the significant efforts for the modeling of gaseous flames using robust turbulence models coupled with the tabulated flamelet-based chemistry approach to considerably reduce computing cost. The exclusive use of a commercial CFD code widely used in the industry allows a direct application of this simulation approach to industrial configurations while keeping computing cost reasonable. Originality/value – This study is useful to engineers interested in designing combustors of gas turbines and others combustion systems fed with liquid fuels.

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Gallot-Lavallée, S., W. P. Jones e A. J. Marquis. "Large Eddy Simulation of an Ethanol Spray Flame with Secondary Droplet Breakup". Flow, Turbulence and Combustion 107, n.º 3 (1 de abril de 2021): 709–43. http://dx.doi.org/10.1007/s10494-021-00248-z.

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AbstractA computational investigation of three configurations of the Delft Spray in Hot-diluted Co-flow (DSHC) is presented. The selected burner comprises a hollow cone pressure swirl atomiser, injecting an ethanol spray, located in the centre of a hot co-flow generator, with the conditions studied corresponding to Moderate or Intense Low-oxygen Dilution (MILD) combustion. The simulations are performed in the context of Large Eddy Simulation (LES) in combination with a transport equation for the joint probability density function (pdf) of the scalars, solved using the Eulerian stochastic field method. The liquid phase is simulated by the use of a Lagrangian point particle approach, where the sub-grid-scale interactions are modelled with a stochastic approach. Droplet breakup is represented by a simple primary breakup model in combination with a stochastic secondary breakup formulation. The approach requires only a minimal knowledge of the fuel injector and avoids the need to specify droplet size and velocity distributions at the injection point. The method produces satisfactory agreement with the experimental data and the velocity fields of the gas and liquid phase both averaged and ‘size-class by size-class’ are well depicted. Two widely accepted evaporation models, utilising a phase equilibrium assumption, are used to investigate the influence of evaporation on the evolution of the liquid phase and the effects on the flame. An analysis on the dynamics of stabilisation sheds light on the importance of droplet size in the three spray flames; different size droplets play different roles in the stabilisation of the flames.

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Zhang, Yan, Hu Wang, Ambrus Both, Likun Ma e Mingfa Yao. "Effects of turbulence-chemistry interactions on auto-ignition and flame structure for n-dodecane spray combustion". Combustion Theory and Modelling 23, n.º 5 (1 de junho de 2019): 907–34. http://dx.doi.org/10.1080/13647830.2019.1600722.

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Gao, Wei, Jinhu Yang, Yong Mu, Fuqiang Liu, Shaolin Wang, Kaixing Wang, Cunxi Liu, Gang Xu e Junqiang Zhu. "Injector-injector interactions on the flow field, spray characteristics, and subsequent flame pattern in an annular combustor". International Journal of Heat and Fluid Flow 98 (dezembro de 2022): 109066. http://dx.doi.org/10.1016/j.ijheatfluidflow.2022.109066.

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42

Vinogradov, Viacheslav A., Yurii M. Shikhman e Corin Segal. "A Review of Fuel Pre-injection in Supersonic, Chemically Reacting Flows". Applied Mechanics Reviews 60, n.º 4 (1 de julho de 2007): 139–48. http://dx.doi.org/10.1115/1.2750346.

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Developing an efficient, supersonic combustion-based, air breathing propulsion cycle operating above Mach 3.5, especially when conventional hydrocarbon fuels are sought and particularly when liquid fuels are preferred to increase density, requires mostly effective mechanisms to improve mixing efficiency. One way to extend the time available for mixing is to inject part of the fuel upstream of the vehicle’s combustion chamber. Injection from the wall remains one of the most challenging problems in supersonic aerodynamics, including the requirement to minimize impulse losses, improve fuel-air mixing, reduce inlet∕combustor interactions, and promote flame stability. This article presents a review of studies involving liquid and, in selected cases, gaseous fuel injected in supersonic inlets or in combustor’s insulators. In all these studies, the fuel was injected from a wall in a wake of thin swept pylons at low dynamic pressure ratios (qjet∕qair=0.6–1.5), including individual pylon∕injector geometries and combinations in the inlet and combustor’s isolator, a variety of injection conditions, different injectants, and evaluated their effects on fuel plume spray, impulse losses, and mixing efficiency. This review article cites 47 references.

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43

Friedman, Jacob A., e Metin Renksizbulut. "Investigating a methanol spray flame interacting with an annular air jet using phase-Doppler interferometry and planar laser-induced fluorescence". Combustion and Flame 117, n.º 4 (junho de 1999): 661–84. http://dx.doi.org/10.1016/s0010-2180(98)00136-9.

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Yang, Jinhu, Cunxi Liu, Fuqiang Liu, Yong Mu e Gang Xu. "The quantitative characterization of the ignition process for a lean staged injector: Influence of the air split between pilot swirlers". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, n.º 5 (27 de dezembro de 2019): 1132–45. http://dx.doi.org/10.1177/0954410019896877.

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The ignition of a lean staged injector aimed at aeronautical application is a transient and complex phenomenon, which involves fluid dynamics, turbulent mixing, chemical kinetics, as well as their mutual interactions. In the present research, a staged injector, designed based on stratified partially premixed combustion concept, is introduced. The ignition performance of stratified partially premixed injectors with different air split ratios between pilot swirlers are experimentally acquired, which exhibits apparent distinctions. In order to make quantitative analyses, the classical physical ignition model is improved, in which the flame propagation process is further divided into the axial and radial propagation sub-processes. Nonreacting flow field and discrete phase simulations, validated by experiment results, are utilized to obtain the velocity and spray distributions. Physical parameters characterizing the ignition sub-processes are defined and calculated based on the numerical simulation results. Conclusions are made by comparing the physical parameters of the ignition sub-processes. The radial propagation of the ignition kernel is responsible for the ignition performance difference between the two injectors with different pilot air split ratios (PASR) in that the average equivalence ratio along the radial propagation route of PASR = 7:3 is one order richer than that of PASR = 2:8. The present ignition analysis and model can be further extended and developed for the optimization of ignition performance of lean staged injector.

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45

Lefebvre, A. H. "The Role of Fuel Preparation in Low-Emission Combustion". Journal of Engineering for Gas Turbines and Power 117, n.º 4 (1 de outubro de 1995): 617–54. http://dx.doi.org/10.1115/1.2815449.

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The attainment of very low pollutant emissions, in particular oxides of nitrogen (NOx), from gas turbines is not only of considerable environmental concern but has also become an area of increasing competitiveness between the different engine manufacturers. For stationary engines, the attainment of ultralow NOx has become the foremost marketing issue. This paper is devoted primarily to current and emerging technologies in the development of ultralow emissions combustors for application to aircraft and stationary engines. Short descriptions of the basic design features of conventional gas turbine combustors and the methods of fuel injection now in widespread use are followed by a review of fuel spray characteristics and recent developments in the measurement and modeling of these characteristics. The main gas-turbine-generated pollutants and their mechanisms of formation are described, along with related environmental risks and various issues concerning emissions regulations and recently enacted legislation for limiting the pollutant levels emitted by both aircraft and stationary engines. The impacts of these emissions regulations on combustor and engine design are discussed first in relation to conventional combustors and then in the context of variable-geometry and staged combustors. Both these concepts are founded on emissions reduction by control of flame temperature. Basic approaches to the design of “dry” low-NOx and ultralow-NOx combustors are reviewed. At the present time lean, premix, prevaporize combustion appears to be the only technology available for achieving ultralow NOx emissions from practical combustors. This concept is discussed in some detail, along with its inherent problems of autoignition, flashback, and acoustic resonance. Attention is also given to alternative methods of achieving ultralow NOx emissions, notably the rich-burn, quick-quench, lean-burn, and catalytic combustors. These concepts are now being actively developed, despite the formidable problems they present in terms of mixing and durability. The final section reviews the various correlations now being used to predict the exhaust gas concentrations of the main gaseous pollutant emissions from gas turbine engines. Comprehensive numerical methods have not yet completely displaced these semi-empirical correlations but are nevertheless providing useful insight into the interactions of swirling and recirculating flows with fuel sprays, as well as guidance to the combustion engineer during the design and development stages. Throughout the paper emphasis is placed on the important and sometimes pivotal role played by the fuel preparation process in the reduction of pollutant emissions from gas turbines.

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Pramanik, Santanu, e Achintya Mukhopadhyay. "Numerical Study of Counterflow Diffusion Flame and Water Spray Interaction". Journal of Thermal Science and Engineering Applications 8, n.º 1 (11 de novembro de 2015). http://dx.doi.org/10.1115/1.4030735.

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This paper reports numerical investigation concerning the interaction of a laminar methane–air counterflow diffusion flame with monodisperse and polydisperse water spray. Commercial code ansys fluent with reduced chemistry has been used for investigation. Effects of strain rate, Sauter mean diameter (SMD), and droplet size distribution on the temperature along stagnation streamline have been studied. Flame extinction using polydisperse water spray has also been explored. Comparison of monodisperse and polydisperse droplet distribution on flame properties reveals suitability of polydisperse spray in flame temperature reduction beyond a particular SMD. This study also provides a numerical framework to study flame–spray interaction and extinction.

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Ogawa, Hideyuki, Tomoki Ishikawa, Yoshimitsu Kobashi e Gen Shibata. "Influence of spray-to-spray interaction after wall impingement of spray flames on diesel combustion characteristics". International Journal of Engine Research, 25 de julho de 2024. http://dx.doi.org/10.1177/14680874241260363.

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The influence of spray-to-spray interaction after wall impingement of spray flames on the combustion characteristics in high pressure and high temperature ambient gas like in combustion chambers of diesel engines was examined with a constant volume vessel. Fuel was injected onto a flat wall from two nozzles to form two parallel, adjacent sprays in the vessel, causing the spray-to-spray interaction after the wall impingement. The combustion was analyzed with the rate of heat release calculated from the pressure transition in the vessel and the spray flame was visualized by high-speed video. The 310 nm UV light images of the chemiluminescence from OH radicals are recorded to demonstrate the reaction activity in the spray flame. The images of transmitted light throughout the constant volume vessel were recorded to visualize the soot formation and oxidation processes as well as to quantify the soot concentrations as the KL factors. The results showed that the rate of heat release from the main combustion decreases and the afterburning increases with the spray-to-spray interaction after the wall impingement of the spray flame. Combustion suppression with the spray-to-spray interaction occurred in all the conditions of the experiments here when changing the distance from the nozzle to the impinging wall between 25 and 40 mm and the fuel injection pressures between 100 and 200 MPa. Inside the spray-to-spray interaction zone, the chemiluminescence from OH radicals is weaker, supporting the inactive combustion due to difficulties of the air entrainment, and the lower transmitted light intensities with larger KL factors, indicating higher soot concentrations. The spray-to-spray interaction zone on the impingement wall advances toward the inside of the vessel between the sprays and it moves away from the wall, entraining the unutilized air and causing a relatively active combustion as well as rapid soot oxidation during the late afterburning stage.

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Bieber, M., M. Al-Khatib, F. Fröde, H. Pitsch, M. A. Reddemann, H.-J. Schmid, R. Tischendorf e R. Kneer. "Influence of angled dispersion gas on coaxial atomization, spray and flame formation in the context of spray-flame synthesis of nanoparticles". Experiments in Fluids 62, n.º 5 (17 de abril de 2021). http://dx.doi.org/10.1007/s00348-021-03196-6.

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Abstract Liquid atomization determines the initial conditions for flame formation and particle synthesis. Without a stable flame, high droplet velocities and thus short droplet residence time in the flame may lead to droplets being injected into an extinguished flame, which influences synthesis and final particle output. An experimental investigation of spray formation and flame stability is performed through high-speed visualization. Targeted variation of nozzle geometry is applied to improve spray-flame interaction and compared to a standardized burner. Timescales of spray density and flame fluctuations are quantified and compared, where the latter were significantly larger and hence not correlated. Instead, dispersion gas forms a barrier between spray phase and pilot flame; hence, ignition depends on large liquid lumps with high radial momentum to break through the dispersion gas for spray ignition. Angling of dispersion gas flow increases radial shear and turbulence and leads to refined atomization and improved flame stability. To investigate the nozzle influence on particle formation, particle characteristics are examined by online and offline analytics with focus on particle structures and product purity. The modified nozzle produced smaller primary particle sizes, thus indicating a sensitivity of sintering dominance on the nozzle geometry. Impurities impact the examination of particle structures and general particle functionality. Carbon contamination was apparent in synthesized particles and also indicated sensitivity to nozzle geometry. Discrepancies to literature data are discussed regarding differences in flame activity and droplet characteristics. The report highlights, how product characteristics can differ crucially due to changes in nozzle geometry despite comparable operating conditions. Graphic abstract

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Zhong, Lijia, Wanhui Zhao, Haiqiao Wei, Gequn Shu e Lei Zhou. "A novel concept of pre-chamber turbulent jet ignition-induced liquid ammonia spray flame". Physics of Fluids 36, n.º 12 (1 de dezembro de 2024). https://doi.org/10.1063/5.0239805.

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Ammonia is one of the most promising alternative fuels owing to its nature of zero-carbon emission. However, the weak ignition characteristic of ammonia imposes a great hindrance on its application on engines. In the present work, a novel concept of pre-chamber turbulent jet ignition (TJI) induced liquid ammonia spray flame based on a high-pressure injection in a constant-volume chamber is proposed. The ignition modes associated with flame development of the transient ammonia spray flame are investigated. The effects of mixture reactivity in the pre-chamber and turbulent jet velocity are investigated. During the TJI-induced ammonia spray flame process, the three distinguished stages, including pre-chamber combustion, partially premixed combustion, and mixing-controlled combustion, are observed. The ignition takes place in the jet-liquid ammonia spray interaction region, but the flame fails to stabilize and propagates downstream along the ammonia spray. However, a spray flame is ignited when the hot combustion products are re-entrained by the ammonia spray, with the liftoff length gradually decreasing. The effects of mixture reactivity are further explored by enriching the pre-chamber mixture to φp = 3. The results indicate that a richer mixture can extend the ignition ability, as the critical oxygen concentration necessary for successful ignition decreases. In addition, a combustion mode transition of extinction-re-ignition phenomenon of spray flame is observed. The fundamental mechanism for the extinction-re-ignition phenomenon is attributed to the cooling effect of flash boiling and re-entrainment of hot combustion products. Furthermore, different nozzle diameters are employed to study the effects of turbulent jet velocity on the ignition tolerance. It can be concluded that a lower turbulent jet velocity can extend the ignition ability in two aspects. On the one hand, the slower hot jet increases the ignition energy by enabling a sufficient mixing between the hot jet and the ammonia spray. On the other hand, the reduced turbulence intensity weakens the turbulent heat dissipation that suppresses ignition. This work provides insightful views for ammonia compression engines.

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Fan, Chengyuan, Daoyuan Wang, Keiya Nishida e Yoichi Ogata. "Visualization of diesel spray and combustion from lateral side of two-dimensional piston cavity in rapid compression and expansion machine". International Journal of Engine Research, 13 de outubro de 2020, 146808742096229. http://dx.doi.org/10.1177/1468087420962298.

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Effect of spray/wall interaction in a rapid compression and expansion machine on mixture formation, ignition location, and soot generation was investigated. A two-dimensional piston cavity designed as the cross section of a reentrant piston was utilized to observe the spray and combustion process from the lateral side. The experiment was conducted at 120 MPa injection pressure under single and split injection strategies with an ambient gas of 15% O2 concentration. A shadow methodology was applied to investigate the interaction between the fuel spray and the piston cavity. Combined with the natural flame luminosity captured by a high-speed color video camera, the behaviors of the impinging spray and the combustion process were studied. The combustion characteristics of the in-cylinder pressure, heat release and combustion phase were recorded and analyzed simultaneously. The results showed that the split injection strategies effectively softened the heat release trace and promoted the onset of the main combustion. The cool-flame phenomenon was captured by using the high-speed color video camera, and the intense ignition was observed when the pilot spray was controlled to impinge on the lower lip of the piston rim. Moreover, results also showed that further extending the mixing process of the pilot spray is inclined to form a homogeneous mixture which was beneficial for the promotion of low-temperature combustion and the reduction of soot generation. This research provides a detailed investigation on the spray and combustion process and it highlights the significant effect of spray/wall interaction on the subsequent combustion process.

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