Academic literature on the topic 'Flame-Spray interaction'

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.

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.

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.

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.

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.

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.

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.

Les systèmes d'extinction incendie aujourd'hui employés pour la protection des véhicules militaires terrestres utilisent le gaz FM200, qui répond à une exigence du protocole de Montréal sur les espèces qui réduisent la couche d'ozone. Cependant, le potentiel de réchauffement global important de ce gaz appelle aujourd'hui à un remplacement urgent. En parallèle, la recherche sur le brouillard d'eau s'est intensifiée depuis les années 1990, en tant que dispositif d'extinction sans appauvrissement de la couche d'ozone, ni potentiel de réchauffement global. Dans le cadre de cette thèse, l'objectif est d'étudier la faisabilité d'un brouillard d'eau additivée comme système d'extinction incendie pour la protection des compartiments moteurs de véhicules militaires et civiles. En effet, l'eau pulvérisée sous forme de brouillard peut être additivée de substances qui modifient ses propriétés physico-chimiques et procurent à la solution résultante de meilleures caractéristiques et des performances d'extinction accrues. Une revue exhaustive de la littérature a notamment permis de mettre en évidence l'existence paradoxale des solvants, espèces hautement inflammables, comme additifs pour le brouillard d'eau. Afin de pouvoir quantifier l'ajout de ces espèces sur les performances d'extinction, une première étape a consisté à caractériser l'interaction entre une flamme et un brouillard d'eau, en présence d'une ventilation variable. Des mesures de vélocimétrie par imagerie de particules ont notamment permis d'identifier des valeurs critiques de ventilation et de pression d'injection. Dans un second temps, un brouillard d'eau additivée aux solvants, en concentrations variables, a été étudié au travers de sept alcools primaires linéaires, du méthanol à l'heptanol. Une analyse statistique a permis d'identifier le pentanol et le butanol comme les meilleurs alcools primaires linéaires en tant qu'additifs pour le brouillard d'eau. La diminution du temps d'extinction par rapport à l'eau seule provient du refroidissement accru de la zone de la flamme apporté par les additifs alcoolisés
The fire extinguishing systems currently used to protect military land vehicles use the gas FM200, which meets a requirement of the Montreal Protocol on species that deplete the ozone layer. However, its significant global warming potential means it urgently needs to be replaced. At the same time, research on water mist has intensified since the 1990s, as a fire extinguishing system that neither depletes the ozone layer nor has a global warming potential. The aim of this thesis is to study the feasibility of a water mist with additives as a fire extinguishing system for the protection of the engine compartments of military and civilian vehicles. The finely sprayed water can be added with substances that modify its physical and chemical properties and give the resulting solution improved characteristics and extinguishing performance. An exhaustive review of the literature has highlighted the paradoxical existence of solvents, highly flammable species, as additives for the water mist. In order to quantify the impact of these species on the extinguishing performance, the first step was to characterize the interaction between a flame and a water mist, in the presence of variable ventilation. Particle image velocimetry measurements were used to identify critical values for ventilation and injection pressure. Secondly, a solvent-added water mist in varying concentrations was studied using seven linear primary alcohols, from methanol to heptanol. A statistical analysis identified pentanol and butanol as the best linear primary alcohols as water mist additives. The reduction of the extinguishing time compared with only water is due to the increased cooling of the flame zone provided by the alcohol additives

[EN] The potential of diesel engines in terms of robustness, efficiency and energy density has made them widely used as power generators and propulsion systems. Specifically, fuel atomization, vaporization and air-fuel mixing, have a fundamental effect on the combustion process, and consequently, a direct impact on pollutant formation, fuel consumption and noise emission. Since the combustion chamber has a limited space respect to the spray penetration, wall impingement is considered to be a common event in direct injection diesel engines, having a relevant influence in the spray evolution and its interaction with both surrounding air and solid walls. This makes of spray-wall interaction an important factor for the combustion process that is still hardly understood. At cold-start conditions, the low in-chamber pressures and temperatures promote the deposition of fuel in the piston wall, which leads to a boost in the formation of unburned hydrocarbons. Additionally, modern design trends such as the increment of rail pressures in injection systems and the progressive reduction of the engine displacement, favor the emergence of spray collision onto the walls. In spite of the evident relevance of the comprehension of this phenomenon and the efforts of engine researchers to reach it, the transient nature of injection process, its small time scales and the complexity of the physical phenomena that take place in the vicinity of the wall, make challenging the direct observation of this spray-wall interaction. Even though computational tools have proven to be priceless in this field of study, the need for reliable experimental data for the development of those predictive models is present. This thesis is aimed to shed light on the fundamental characteristics of spray-wall interaction (SWI) at diesel-like chamber conditions. A flat wall was set at different impingement distances and angles respect to the spray. In this way, two different kinds of experimental investigations on colliding sprays were carried out: A transparent quartz wall was employed into the chamber to, in isolation, analyze the macroscopic characteristics of the spray at both evaporative inert and reactive conditions, which have been observed laterally and through the wall, thanks to the use of a high-pressure and high-temperature vessel with optical accesses. This same test rig was used in the second kind of experiments, where instead of the quartz plate, a stainless steel wall was used to capture the effect of the operating conditions on the heat flux between the wall and the spray during the injection-combustion events and to determine how spray and flame evolution are affected by realistic heat transfer situations. This wall was instrumented to control its initial in-chamber surface temperature and to measure its variation with time by using high-speed thermocouples. Tests at free-jet conditions were also performed in order to provide a solid comparative base for those experiments.
[ES] El potencial de los motores diesel en términos de robustez, eficiencia y la densidad de energía los ha hecho ser ampliamente usados como generadores de energía y sistemas propulsivos. Específicamente, la atomización de combustible, vaporización y mezcla de aire y combustible tienen un efecto fundamental en el proceso de combustión y, en consecuencia, un impacto directo en la formación de emisiones contaminantes, consumo de combustible y generación de ruido. Dado que la cámara de combustión tiene un espacio limitado con respecto la capacidad de penetración del chorro, el impacto de la pared se considera bastante común en motores de inyección directa diésel, que tienen una influencia relevante en la evolución del chorro y su interacción con el aire circundante y las paredes sólidas. Esto hace de interacción chorro-pared, un factor importante para el proceso de combustión que aún es dificilmente comprendido. En condiciones de arranque en frío, las bajas presiones y temperaturas en la cámara promueven la deposición de combustible en la pared del pistón, lo que conduce a un aumento en los niveles de formación de hidrocarburos no quemados. Además, las tendencias modernas de diseño como el incremento de las presiones de rail en los sistemas de inyección y la progresiva reducción en la cilindrada de los motores, favorecen la aparición de colisiones entre chorro y pared. A pesar de la evidente importancia en la comprensión de este fenómeno y los esfuerzos de los investigadores para alcanzarla, la transitoria naturaleza del proceso de inyección, sus pequeñas escalas de temporales y la complejidad de los fenómenos físicos que tienen lugar en las proximidades de la pared, hacen que la observación directa de esta interacción chorro-pared sea un desafío. Aunque las herramientas computacionales han demostrado ser invaluables en este campo de estudio, la necesidad de datos experimentales confiables para el desarrollo de esos modelos predictivos está muy presente. Esta tesis tiene como objetivo arrojar luz sobre las características fundamentales de la interacción chorro-pared (SWI por sus siglas en inglés) en condiciones de cámara similares a las de un motor diesel. Se colocó una pared plana a diferentes distancias de impacto y ángulos con respecto al jet. De esta manera, dos tipos diferentes de investigaciones experimentales sobre chorros en colisión se llevaron a cabo: se empleó una pared de cuarzo transparente en la cámara para, de forma aislada, analizar las características macroscópicas del chorro en condiciones evaporativas inertes y reactivas, que pueden observarse lateralmente y a través de la pared, gracias al uso de una instalación de alta presión y alta temperatura ópticamente accesible. Esta misma instalación se utilizó en el segundo tipo de experimentos en los que se introdujo una pared de acero inoxidable para capturar adicionalmente el efecto de las condiciones de operación en el flujo de calor entre ésta y el chorro durante los eventos de inyección y combustión y para determinar cómo la evolución del chorro y la llama son afectadas por una situación realista de transferencia de calor. Esta pared fue instrumentada para controlar la temperatura inicial de su superficie expuesta a la cámara y medir su variación con el tiempo, utilizando termopares de alta velocidad. Ensayos en condiciones de chorro libre también se realizaron para proporcionar una base comparativa sólida para esos experimentos.
[CA] El potencial dels motors dièsel en termes de robustesa, eficiència i la densitat d'energia els ha fet ser àmpliament usats com a generadors d'energia i sistemes propulsius. Específicament, l'atomització de combustible, vaporització i barreja d'aire i combustible tenen un efecte fonamental en el procés de combustió i, en conseqüència, un impacte directe en la formació d'emissions contaminants, consum de combustible i generació de soroll. Atès que la cambra de combustió té un espai limitat pel que fa la capacitat de penetració de l'raig, l'impacte de la paret es considera bastant comú en motors d'injecció directa dièsel, que tenen una influència rellevant en l'evolució del doll i la seva interacció amb el aire circumdant i les parets sòlides. Això fa d'interacció doll-paret, un factor important per al procés de combustió que encara és difícilment comprès. En condicions d'arrencada en fred, les baixes pressions i temperatures a la cambra promouen la deposició de combustible a la paret del pistó, el que condueix a un augment en els nivells de formació d'hidrocarburs no cremats. A més, les tendències modernes de disseny com l'increment de les pressions de rail en els sistemes d'injecció i la progressiva reducció en la cilindrada dels motors, afavoreixen l'aparició de col·lisions entre el doll i la paret. Tot i l'evident importància en la comprensió d'aquest fenomen i els esforços dels investigadors per aconseguir-la, la transitòria naturalesa de l'procés d'injecció, les seves petites escales de temporals i la complexitat dels fenòmens físics que tenen lloc en les proximitats de la paret , fan que l'observació directa d'aquesta interacció doll-paret siga un desafiament. Tot i que les eines computacionals han demostrat ser invaluables en aquest camp d'estudi, la necessitat de dades experimentals fiables per al desenvolupament d'aquests models predictius està molt present. Aquesta tesi té com a objectiu donar llum sobre les característiques fonamentals de la interacció doll-paret (SWI per les seues sigles en anglès) en condicions de cambra similars a les d'un motor dièsel. Es va col·locar una paret plana a diferents distàncies d'impacte i angles pel que fa al jet. D'aquesta manera, dos tipus diferents d'investigacions experimentals sobre dolls en col·lisió es van dur a terme: es va emprar una paret de quars transparent a la cambra per, de forma aïllada, analitzar les característiques macroscòpiques del doll en condicions evaporació inerts i reactives, que poden observar lateralment i a través de la paret, gràcies a l'ús d'una instal·lació d'alta pressió i alta temperatura òpticament accessible. Aquesta mateixa instal·lació es va utilitzar en el segon tipus d'experiments en els quals es va introduir una paret d'acer inoxidable per capturar addicionalment l'efecte de les condicions d'operació en el flux de calor entre aquesta i el dull durant els esdeveniments d'injecció i combustió i per determinar com l'evolució del doll i la flama són afectades per una situació realista de transferència de calor. Aquesta paret va ser instrumentada per controlar la temperatura inicial de la seua superfície exposada a la càmera i mesurar la seua variació amb el temps, utilitzant termoparells d'alta velocitat. Assajos en condicions de doll lliure també es van realitzar per proporcionar una base comparativa sòlida per a aquests experiments.
Peraza Ávila, JE. (2020). Experimental study of the diesel spray behavior during the jet-wall interaction at high pressure and high temperature conditions [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/149389
TESIS

Abstract This paper will outline the results of a study underway at Utah State University aimed at developing technology to alter the direction and profile of thermal spray flows using the Coanda effect. Coanda-assisted Spray Manipulation (CSM) makes use of an enhanced Coanda effect on axisymmetric geometries through the interaction of a high volume primary jet flowing through the center of a collar and a secondary high-momentum jet parallel to the first and adjacent to the convex collar. The control jet attaches to the convex wall and vectors according to Coanda effect principles, entraining and vectoring the primary jet, resulting in controllable r - θ directional spraying. The basic turning effect was investigated in a fundamental experimental study. The results of the fundamental study were applied to the design of an add-on CSM attached to a Metco 2P powder flame spray gun.

Abstract Lean premixed prevaporized combustors often feature staged combustion with a premixed main flame anchored by the nonpremixed pilot flame to obtain a wide operating range. Interaction between pilot flame and main flame is complex. The present article investigates the flame topologies and flame-fuel interactions in separated stratified swirl flames under various operating conditions (fuel to air ratio FAR and fuel stage ratio α) and injector designs (main stage swirl number Sm and fuel injection angle JA). Experiments are carried out in the centrally staged optical model combustor at inlet pressure P3 = 0.49–0.7 MPa and inlet temperature T3 = 539 K. At first, the flame structures obtained from OH-PLIF are investigated and discussed for the baseline injector (Sm = 0.9, JA = −50°). The V-shaped flame is stabilized in the inner shear layer (ISL) with the flame attachment point located at the lip for the pilot flame mode (α = 1). Dual flame is observed in the combustor for the fuel staged combustion (α < 1): the main flame stabilized in the outer shear layer (OSL) and the pilot flame stabilized in the inner shear layer (ISL). For increasing α from 0.15 to 0.25, gaps between the main flame and pilot flame are decreased, indicating a stronger interaction between the two flames. The flame structure for different injector geometries is then investigated. It is found that the higher main stage swirl number induces a larger flame opening angle, decreasing the interaction between two flames. Fuel injected into crossflow (JA = −50°) is found to generated a more separated flame, decreasing the flame interactions. Finally, fuel distribution measured by kerosene-PLIF is analyzed with the correlation to flame structure. Results show that the existence of a good mixing of fuel and fresh air in ISL and OSL provide favorable conditions for chemical reaction with high heat release. The OH distribution is highly correlated to fuel distribution. The fuel zone is located at the inner side of high OH region, indicating the reaction and heat release take place after the mixing of preheating of fuel-air mixture.

A numerical investigation of the interaction between a spray flame and an acoustic forcing of the velocity field is presented in this paper. The test-case which is the focus of this work is a non-confined flame1,2 burning at atmospheric pressure and therefore the velocity fluctuations play a key role. Acoustic waves will eventually affect the rate of combustion, and the oscillating fluctuation of the heat released by the flame might be increased by the evaporation process. The dynamic interaction between the evaporating fuel spray and the velocity fluctuations induced by an acoustic perturbation is investigated to understand the impact of the acoustic waves on the droplet dispersion and on the evaporation rate. The influence of the initial droplet diameter has been observed to be irrelevant, when two monodispersed sprays of 20 μm and 80 μm were numerically simulated. In this work the main question to address is how the interphase heat and mass transfer, and the momentum exchange are influenced, at low amplitude velocity fluctuations, by the forcing frequency, under two different imposed velocity profiles of the liquid fuel. A fast decay of the slip velocity is predicted under both steady and perturbed conditions. Thus, slip velocity fluctuations do not have a significant influence on the solved spray field. Finally, the impact of the forcing frequency and of the pilot are the main effects acting on the forced flame response. At low frequency, the entrainment of hot gases into the spray results in a clearly visible stretching of the flame which causes a high level of temperature fluctuation. At high frequency, despite the weak response of the gas velocity field, the dynamics of the combustion show a faster evaporation rate than the acoustic–free case.

Water injection is often used to control NOx emissions or to increase power output from non-premixed combustion of gaseous and liquid fuels. Since the emission level in premixed natural gas combustion is significantly lower than for non-premixed combustion, water injection for emission reduction is usually not an issue. However, the increasing share of fluctuating power output from renewables motivates research activities on the improvement of the operational flexibility of combined cycle power plants. One aspect in that context is power augmentation by injection of liquid water in premixed combustors without drawbacks regarding emissions and flame stability. For research purposes, water injection technology has therefore recently been transferred to premixed combustors burning natural gas. In order to investigate the influence of water injection on premixed combustion of natural gas, an atmospheric single burner test rig has been set up at Lehrstuhl für Thermodynamik, TU München. The test rig is equipped with a highly flexible water injection system to study the influence of water atomization behavior on flame shape, position and stabilization. Presented investigations are conducted at gas turbine like preheating temperatures (673K) and flame temperatures (1800–1950K) to ensure high technical relevance. In this paper, the interaction between water injection, atomization and macroscopic flame behavior is outlined. Favorable and non-favorable operating conditions of the water injection system are presented in order to clarify the influence of water atomization and vaporization on flame stability and the emission behavior of the test rig. Water spray quality is assessed externally with a Malvern laser diffraction spectrometer whereas spray distribution in the test rig is determined by means of Mie scattering images at reacting conditions. The flame shape is analyzed using time-averaged OH* chemiluminescence images while the efficiency of water injection at various operating points is evaluated using global emission concentration measurements. Finally, the important influence of the water injection system design on the combustor performance will be shown using combined Mie scattering and OH* chemiluminescence images. At constant adiabatic flame temperatures, a stable flame could be established for water-to-fuel ratios of up to 2.25. While only minor changes could be detected for the heat release distribution in the combustion chamber, the water distribution changes significantly while increasing the amount of water. Finaly, changes in NOx emission concentrations can directly be related to water droplet sizes and the global water distribution in the combustion chamber.

Abstract The various thermal spraying methods available include the plasma process, which uses a plasma flame to melt a fine powder before it is sprayed onto a substrate, and the High Velocity Oxy-Fuel (HVOF) spray process, in which the flame is made from the combustion of oxygen. These methods differ both in the temperature and velocity with which the molten particles impact the substrate, leading to different coating characteristics. This includes differences in splat morphology and the nature of microstructural interactions at the splat-substrate interface. That is, features such as local melting of the substrate, the existence of porosity and the presence of oxides. For this study a nickel-chromium powder was sprayed onto mirror-polished stainless steel substrates using both plasma spray and HVOF to form single splats. These splats, and their interface with the substrate, were characterized using a range of microstructural characterization techniques and the observed differences were correlated to the spray conditions used.

A two-staged swirling burner is numerically simulated through large eddy simulations. The impact of the liquid phase modeling approach is evaluated comparing the Eulerian and Lagrangian frameworks for two different operation points, full pilot injection and full multipoint injection. For the full multipoint injection, since the operation point is closer to a Lean Premixed Prevaporized (LPP) regime, both liquid phase models present similar flame structure (an M flame). For the full pilot injection, Eulerian and Lagrangian approaches result in different flames for equivalent boundary conditions: the Eulerian simulation produces a ‘tulip’ flame, while the Lagrangian spray forms a lifted flame. To assess the model sensitivity to boundary conditions parameters, complementary Lagrangian simulations are made varying injected droplets’ diameter and spray angle, this time resulting in a ‘tulip’ flame very similar to the Eulerian one. Finally, a last Eulerian simulation is made, where the injected droplets’ diameter is increased, still leading to a ‘tulip’ flame, showing that the strong interaction between liquid phase and flame highly impact the results.

Burners operating in lean premixed prevaporized (LPP) regimes are considered as good candidates to reduce pollutant emissions from gas turbines. Lean combustion regimes result in lower burnt gas temperatures and therefore a reduction on the NOx emissions, one of the main pollutant species. However, these burners usually show strong flame dynamics, making them prone to various stabilization problems (combustion instabilities, flashback, flame extinction). To face this issue, multi-injection staged combustion can be envisaged. Staging procedures enable fuel distribution control, while multipoint injections can lead to a fast and efficient mixing. A laboratory-scale staged multipoint combustor is developed in the present study, in the framework of LPP combustion, with an injection device close to the industrial one. Using a staging procedure between the primary pilot stage and the secondary multipoint one, droplet and velocity field distributions can be varied in the spray that is formed at the entrance of the combustion chamber. The resulting spray and the flame are characterized using OH-Planar Laser Induced Fluorescence, High Speed Particle Image Velocimetry and Phase Doppler Anemometry measurements. Three staging values, corresponding to three different flame stabilization processes, are analyzed, while power is kept constant. It is shown that mean values are strongly influenced by the fuel distribution and the flame position. Using adequate post-processing, the interaction between the acoustic field and the droplet behavior is characterized. Spectral analysis reveals a strong acoustic-flame coupling leading to a low frequency oscillation of both the velocity field and the spray droplet distribution. In addition, acoustic measurements in the feeding line show that a strong oscillation of the acoustic field leading to a change in fuel injection, and hence droplet behavior.

Abstract Spray impingement in internal combustion engines has received great attentions. Such a phenomenon is especially important for diesel spray because the spray and combustion characteristics are significantly altered by the impingement. In this study, numerical investigations of impinged reacting spray jets in a constant volume combustion chamber were performed to understand the spray and flame structure under high pressure and high temperature conditions. The 3-D computational fluid dynamics (CFD) CONVERGE code was selected as the numerical tool to perform Large-eddy simulations (LES) to understand the process of spray combustion-wall interaction. CFD models were validated against experimental results in terms of spray penetration and ignition delay at inert and reacting spray conditions. The temperature and soot mass fraction profiles near the impinging plate were investigated for 900 and 1000 K ambient conditions. It was found that soot mass fraction is generally increased near the impinging plate as the temperature is decreased. The heat transfer from the flame to the plate makes the temperature close to the wall more favorable for soot formation. A dense soot core was observed at the leading edge when the injection was still happening because the vortex there took the opportunity from existing burned gas to new fuel to meet the ambient air. A soot layer was observed stick on the wall as the air was hard to entrain the flame all the way to the plate side.

Abstract Recent investigations of combustion instabilities in annular systems indicate that considerable insight may be gained by using information gathered in single-sector experiments. Such experiments are, for example, employed to measure flame describing functions (FDFs), which represent the flame response to incident perturbations. These data may be used in combination with low-order models to interpret instabilities in multiple injector annular systems. It is known, however, that the structure and dynamical behavior of an isolated flame do not necessarily coincide with those of a flame placed in an annular environment with neighboring side flames. It is then worth analyzing effects that may be induced by the difference in lateral boundary conditions and specifically examining the extent to which the FDF data from single-segment experiments portrays the dynamical response of the flame in the annular environment. These issues are investigated with a new setup, named TICCA-Spray, that comprises a linear arrangement of three injectors. The central flame is surrounded by two identical side flames in a rectangular geometry with key dimensions, side-wall separation, and spacing between injectors identical to those of the annular system MICCA-Spray. The describing function of the central flame is determined with techniques recently developed in single sector experiments (SICCA-Spray). The FDFs obtained in the two configurations are compared for two swirler types having different swirl numbers and pressure drops. The effect of the swirl direction of the neighboring injectors is also explored by operating with co- and counter-swirl combinations. Differences between FDFs determined in the two test facilities, sometimes modest and in other cases less negligible, are found to depend on the flames’ spatial extension and interactions. The general inference is that the FDFs measured in a single-injector combustor are better suited if the flame-wall interaction is weak, and provided that the area is equivalent to that of a single sector of an annular combustor. Nonetheless, using a multi-injector system would be more appropriate for a more precise FDF determination.