Auswahl der wissenschaftlichen Literatur zum Thema „Optically Accessible Burners“

Direct-injection in spark-ignition engines has long been recognized as a valid option for improving fuel economy, reducing CO2 emissions and avoiding knock occurrence due to higher flexibility in control strategies. However, problems associated with mixture formation are responsible for soot emissions, one of the most limiting factors of this technology. Therefore, the combustion process and soot formation were investigated with different injection strategies on a gasoline direct injection (GDI) engine. The experimental analysis was realized on an optically accessible single cylinder engine when applying single, double and triple injection strategies. Moreover, the effect of fuel delivery phasing was also scrutinized by changing the start of the injection during late intake- and early compression-strokes. The duration of injection was split in different percentages between two or three pulses, so as to obtain close to stoichiometric operation in all conditions. The engine was operated at fixed rotational speed and spark timing, with wide-open throttle. Optical diagnostics based on cycle resolved digital imaging was applied during the early and late stages of the combustion process. Detailed information on the flame front morphology and soot formation were obtained. The optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. The results suggest that the split injection of the fuel has advantages in terms of reduction of soot formation and NOx emissions and a similar combustion performance with respect to the single injection timing. Moreover, an early injection resulted in higher rates of heat release and in-cylinder pressure, together with a reduction of soot formation and flame distortion. The double injection strategy with higher percentage of fuel injected in the first pulse and early second injection pulse showed the best results in terms of combustion evolution and pollutant emissions. For the operative condition studied, a higher time for mixture homogenization and split of fuel injected in the intake stroke shows the best results.

Abstract A detailed investigation on flame structures and stabilization mechanisms of confined high momentum jet flames by one-dimensional (1D)-laser Raman measurements is presented. The flames were operated with natural gas (NG) at gas turbine relevant conditions in an optically accessible high-pressure test rig. The generic burner represents a full scale single nozzle of a high temperature FLOX® gas turbine combustor including a pilot stage. 1D-laser Raman measurements were performed on both an unpiloted and a piloted flame and evaluated on a single shot basis revealing the thermochemical states from unburned inflow conditions to burned hot gas in terms of average and statistical values of the major species concentrations, the mixture fraction and the temperature. The results show a distinct difference in the flame stabilization mechanism between the unpiloted and the piloted case. The former is apparently driven by strong mixing of fresh unburned gas and recirculated hot burned gas that eventually causes autoignition. The piloted flame is stabilized by the pilot stage followed by turbulent flame propagation. The findings help to understand the underlying combustion mechanisms and to further develop gas turbine burners following the FLOX concept.

An optically accessible single-cylinder spark-ignition engine operated under homogeneous, part-load conditions is experimentally investigated using optical and spark diagnostics to evaluate the relationship between the spark, flow, and flame with increasing dilution using several levels of exhaust gas recirculation (EGR). Voltage and current measurements of the secondary spark circuit are compared with simultaneous high-speed spark plasma imaging, particle image velocimetry measurements of the flow field, and burned gas images. Specifically, characteristic restrike cycles and normal cycles are examined under the 0 % EGR and 12.9 % EGR conditions to reveal a relationship between the magnitude and direction of the velocity near the spark plug and the spark’s behavior coupled with that of the subsequent flame propagation. Through the use of conditional statistics and correlation analysis of data sets of all non-restrike and all restrike cycles, the horizontal velocity across the spark gap was identified as a critical quantity in facilitating more stable and faster combustion under diluted mixture conditions.

AbstractSoot formation and oxidation in high-pressure combustion is of high practical relevance but still sparsely investigated because of its experimental complexity. In this work we present a high-pressure burner for studying sooting premixed flames at pressures up to 30 bar. An optically accessible vessel houses a burner that stabilizes a rich premixed ethylene/air flame on a porous sintered stainless-steel plate. The flame is surrounded by a non-sooting rich methane/air flame and an air coflow for reducing temperature gradients, buoyancy-induced instabilities, and heat loss of the innermost flame. Spectrally-resolved soot pyrometry was used for determining gas temperatures. These were introduced into model functions to fit the temporal signal decay curves obtained from two-color time-resolved laser-induced incandescence (TiRe-LII) measurements for extracting soot volume fractions and mean particle size as a function of height above burner and gas pressure. The derived mean particle sizes and soot concentrations were compared against thermophoretically sampled soot analyzed via transmission electron microscopy (TEM) and laser extinction measurements at 785 nm, respectively. Soot volume fractions derived from LII peak signal intensities need to be corrected for signal attenuation at the high soot concentrations present in the investigated flame. From the various heat conduction models employed in deriving mean soot particle diameters from TiRe-LII, the Fuchs model gave remarkably good agreement with TEM on sampled soot at various heights above the burner.

A model FLOX® combustor, featuring a single high momentum premixed jet flame, has been investigated using laser diagnostics in an optically accessible combustion chamber at a pressure of 8 bar. The model combustor was designed as a large single eccentric nozzle main burner (Ø 40 mm) together with an adjoining pilot burner and was operated with natural gas. To gain insight into the flame stabilization mechanisms with and without piloting, simultaneous particle image velocimetry (PIV) and OH laser-induced fluorescence (LIF) measurements have been performed at numerous two-dimensional (2D) sections of the flame. Additional OH-LIF measurements without PIV particles were analyzed quantitatively resulting in absolute OH concentrations and temperature fields. The flow field looks rather similar for both the unpiloted and the piloted cases, featuring a large recirculation zone next to the high momentum jet. However, flame shape and position change drastically. For the unpiloted case, the flame is lifted and widely distributed. Isolated flame kernels are found at the flame root in the vicinity of small-scale vortices. For the piloted flame, on the other hand, both pilot and main flame are attached to the burner base plate, and flame stabilization seems to take place on much smaller spatial scales with a connected flame front and no isolated flame kernels. The single-shot analysis gives rise to the assumption that for the unpiloted case, small-scale vortices act like the pilot burner flow in the opposed case and constantly impinge and ignite the high momentum jet at its root.

Abstract The temperature distribution of a premixed methane air flame running at a Reynolds number of 1300 on a circular burner, 12.7mm diameter, enclosed in a fused silica cylindrical liner has been experimentally reconstructed using a non-invasive approach combining Background Oriented Schlieren (BOS) and Infrared (IR) thermography. BOS is used to characterize both the air ambient to the system, using an existing technique called 3D ray tracing, and the reactive flow inside the enclosure, with a novel modified version of 3D ray tracing. IR thermography is used to characterize the thermal/optical characteristics of the quartz glass enclosure itself since the information is required as BOS is a line of sight imaging technique. Out of necessity, an approximated species independent relationship is used to calculate flow temperature from refractive index. A simulation is used to show this error is in the range of 5.8%-7%. Additionally, it is found that drastically simplifying the approach by removing the IR thermography system entirely and using the near outer wall air temperature from BOS/3D ray tracing to characterize the internal temperature of the quartz liner itself only causes a 1.5%-3.8% degradation in the accuracy of the reconstructed temperature field. The technique as presented is a relatively inexpensive, experimentally simple approach capable of determining the steady state temperature characteristics of optically accessible axisymmetric reactive flows.

An experimental study was conducted on electrically controllable solid propellants (ECSPs) created using a polyethylene oxide polymer binder, lithium perchlorate, and multiwalled carbon nanotubes. The propellants decompose and ignite shortly after the application of a voltage potential and extinguish when the voltage is removed under atmospheric conditions. The ignition delay as a function of the applied voltage magnitude was determined for a range of ECSP compositions. Pressurized experiments were conducted in an optically accessible strand burner to characterize the burning properties of the ECSPs as a function of pressure and electrical power. Additional experiments were conducted at elevated pressures where the voltage potential was removed and reapplied to extinguish and reignite the propellant and determine the self-extinction limits of the ECSPs. The results demonstrate that small compositional changes can drastically impact the ability to extinguish the ECSPs at elevated pressures.

In support of the development of CFD for aeroengine combustion, quantitative measurements of spray properties and temperature were made. A generic swirling air blast injector was designed and built to produce well defined inlet conditions and for ease of numerical description for the CFD development. The measurements were performed in an optically accessible single sector combustor at pressures of 4 and 10 bar and preheat temperatures of 550 and 650 K, respectively. Jet A-1 was used as fuel. The burner air to fuel ratio was 20 and the pressure loss was set to 3%. Sauter mean diameter profiles and liquid mass flux distributions were generated from the phase Doppler anemometry measurements of the evaporating spray drop sizes and velocities. With planar measurements of Mie scattering and kerosene-LIF, the distribution of kerosene (liquid and vapor phase) was imaged. Temperatures were measured with OH-LIF. The burner was designed with a straight outlet to exhibit lifted flames. Hence initial distributions of size, velocity and density of the spray were measured before it entered the flame. Almost complete prevaporization was seen at least for the four bar flame. Compared with atmospheric investigations, the smaller diameters of the droplets and the small streamline curvature of the configuration led to a more uniform behavior of the spray.

Abstract Flashback with subsequent flame anchoring (FA) is an inherent risk of lean premixed gas turbine combustors operated with highly reactive fuel. The present study has been performed to characterize flame stabilization in the premixing zone of a lean premixed swirl stabilized burner and to identify critical combustion characteristics. An optically accessible burner was used for experimental investigations under atmospheric pressure and elevated preheat temperatures. The air mass flow rate, global equivalence ratio and preheat temperature were systematically varied to identify critical operating parameters. Hydrogen-natural gas mixtures with hydrogen mass fractions from 15 to 100 % were studied to evaluate the impact of fuel reactivity. The air-fuel mixture was ignited with a focused single laser pulse to trigger FA in the premixing zone during steady operation. High speed imaging with OH*-chemiluminescence were applied to observe flame characteristics and evaluate flame anchoring propensity. Flame anchoring limits (FAL) are reported in terms of the minimum global equivalence ratio at which the flame was blown out of the premixing zone within a critical time period. A comparison of characteristic time scales at FAL shows that the main impact during flame anchoring is given by the fuel reactivity and to some extent by preheat temperature. A Damköhler criterion is derived from the FAL that allows prediction of FA propensity based on operating conditions and 1-D reacting simulations.

Abstract The effects of partial premixing on a reacting jet-in-crossflow is investigated in a five atmosphere axially staged combustor at stationary gas turbine relevant conditions. The facility consists of a dump style headend burner that provides a crossflow with a quasi-uniform velocity and temperature profile to the axial stage to isolate the effects of the jet-in-crossflow. The headend burner is run with methane and air at a lean equivalence ratio to match industry emission standards. For this work, the total air to the headend and axial stage is kept constant, and fuel is split between the headend and axial stage to represent different gas turbine loading conditions. For the cases analyzed, the fuel split to the axial stage went up to 25%. The axial stage consists of an optically accessible test section with a coaxial injector that provides variability to how long the methane and air can mix before entering the facility. Three different premixed levels are studied: fully premixed, nonpremixed, and partially premixed. The flow-field characteristics of the reacting jet-in-crossflow are analyzed using particle image velocimetry (PIV), and flame behavior is quantified by employing CH* chemiluminescence. NO measurements are made at the exit of the facility using a Horiba emissions analyzer. Two different flames are observed: flames that burn in the leeward recirculation region and flames that burn at the core of the jet.

La transition vers une économie neutre en carbone est confrontée à deux défis majeurs : le stockage de l'excès d'énergie provenant des énergies renouvelables et la décarbonation des processus de combustion dans les secteurs difficiles à électrifier. La stratégie Power to Gas (P2G) propose de résoudre ces problèmes en substituant partiellement l'hydrogène dans le réseau actuel de gaz naturel. Cependant, cela nécessite le développement de brûleurs flexibles capables de s'adapter à des niveaux variables d'hydrogène dans le réseau. Cela est compliqué à cause des différences entre les propriétés de la flamme d’hydrogène et celles des combustibles hydrocarbonés. Les brûleurs poreux (PMBs) sont considérés comme une technologie prometteuse en raison de leurs propriétés uniques. Les PMBs utilisent la recirculation de chaleur pour stabiliser les flammes à l'intérieur de matrices poreuses inertes, incrémentant le taux de consommation de la flamme et atteignant des températures locales superadiabatiques. Cela permet des densités de puissance plus élevées et l’extension des limites d'inflammabilité, ce qui se traduit par des dispositifs compacts et une faible émission de NOx avec des efficacités radiatives élevées.Le mécanisme fondamental de fonctionnement des brûleurs poreux à l'échelle macroscopique, la recirculation de la chaleur, est bien compris. Cependant, il existe encore une connaissance limitée sur certains phénomènes à l'échelle des pores et de leur influence sur le comportement du système global. En raison de la non-linéarité de la combustion et du transfert de chaleur, la stabilisation de la flamme et les performances du brûleur dépendent fortement des détails à l'échelle des pores. Les modèles de bas ordre actuels n'incluent pas la modélisation des interactions flamme-paroi et des effets de diffusion préférentielle, ce qui entraîne une faible précision. Les diagnostics non intrusifs avancés pourraient être utilisés pour étudier la structure locale de la flamme et guider l'amélioration des modèles de bas ordre. Cependant, les mesures expérimentales dans les PMBs sont entravées par le manque d'accès optique à l'intérieur de la matrice poreuse. Malgré les efforts récents, l'application de diagnostics optiques et non intrusifs dans les PMBs est encore très rare. Cette thèse présente une étude expérimentale sur la combustion en milieu poreux et est consacrée au développement de diagnostics optiques. Des PMBs optiquement accessibles sont produits en combinant des topologies définies par ordinateur avec des techniques de fabrication additive. La méthodologie actuelle offre un accès optique étendu dans une configuration de brûleur 3D sans perturber la structure de la matrice. L'accès optique est utilisé pour appliquer une série de diagnostics optiques, y compris la chimiluminescence CH*, l'imagerie de diffusion de Mie et la micro-PIV. Nos résultats montrent les limites des VAMs actuels et de leurs méthodes de validation. La mise en œuvre de diagnostics novateurs a également révélé différentes tendances de stabilisation dans les flammes enrichies en H2, soulignant l'effet des mécanismes d'ancrage local sur les limites de fonctionnement du brûleur. Enfin, l'accès optique est exploité pour effectuer des diagnostics laser et étudier la structure de la flamme à l'échelle des pores. Nos résultats révèlent différents modes de stabilisation et mettent en évidence l'impact de l’écoulement interstitiel sur les performances du brûleur. Cette thèse ouvre de nouvelles voies pour l'application de diagnostics non intrusifs et plaide pour un développement supplémentaire des techniques expérimentales avancées dans les brûleurs poreux
Porous Media Burners (PMBs) are a combustion technology based on heat recirculation where a flame is stabilized within the cavities of an inert porous matrix. In PMBs, heat is transferred upstream from the burned to the unburned gas through the solid matrix yielding a preheating of the reactants.This increases their burning rate allowing for more compact combustion devices and the operation beyond conventional flammability limits. As a result, the stabilization of flames at ultra-lean equivalence ratios is possible, with the subsequent reduction of the flame temperature and NOx emissions. In these burners, a substantial fraction of the power is radiated by the hot solid phase, with radiated power fractions ranging between 20-30 %. This, together with their elevated efficiency and low pollutant emissions, has motivated their commercial use in various infrared heating applications.In the past years, PMBs have received renewed interest owing to their potential as fuel flexible burners. Their ability to stabilize flames over a wide range of burning rates makes them promising candidates to handle the uneven flame properties of hydrogen and hydrocarbon fuels.The mechanism of heat recirculation in PMBs is well understood. However, there is still limited knowledge about many pore-scale phenomena that have a critical impact on the macroscopic behavior of the system and its performance.Advanced nonintrusive diagnostics could be used to study local flame stabilization mechanisms and improve current models. However, experimental measurements in PMBs are hindered by the lack of optical access to the interior of the porous matrix.This dissertation presents an experimental study on porous media combustion and is devoted to the application of optical diagnostics. Optically accessible PMBs are produced by combining computer-defined topologies with additive manufacturing techniques. This methodology provides an extensive optical access in a 3D burner configuration without altering the matrix structure. Optical access is leveraged to apply CH* chemiluminescence, Mie-scattering imaging and micro PIV. Topology tailoring is exploited to analyze the influence of the geometrical parameters of the porous matrix. Direct flame visualization enables the tracking of the reaction region as a function of the operating conditions, which can be used for model validation. The present results bring to light several limitations of current low order models and highlight the influence of the pore size on flame stabilization. Flame-front tracking is also used to investigate the effect of H2-enrichment on the behavior of the flame. This technique reveals different stabilization trends in H2-enriched flames that are not well retrieved by current models. Mie-scattering permits the quantification of the re-equilibration distance and the analysis of the flame shape. Micro PIV measurements show the influence of the topology on the interstitial flow and on the contribution of hydrodynamic effects to flame stabilization.This PhD seeks to open new paths for the application of non-intrusive diagnostics in PMBs and to improve the current understanding of flame stabilization mechanisms

Abstract A detailed investigation on flame structures and stabilization mechanisms of confined high momentum jet flames by 1D-laser Raman measurements is presented. The flames were operated with natural gas (NG) at gas turbine relevant conditions in an optically accessible high pressure test rig. The generic burner represents a full scale single nozzle of a high temperature FLOX® gas turbine combustor including a pilot stage. 1D-laser Raman measurements were performed on both an unpiloted and a piloted flame and evaluated on a single shot basis revealing the thermochemical states from unburned inflow conditions to burned hot gas in terms of average and statistical values of the major species concentrations, the mixture fraction and the temperature. The results are supported by complementary measurement techniques that have been previously conducted and presented in the connected papers part A and B [1,2], such as OH*-chemiluminescence, planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV), that combine to a big picture of the flame structures and help to interpret the results. The results show a distinct difference in the flame stabilization mechanism between the unpiloted and the piloted case. The former is apparently driven by strong mixing of fresh unburned gas and recirculated hot burned gas that eventually causes autoignition. The piloted flame is stabilized by the pilot stage followed by turbulent flame propagation. The findings help to understand the underlying combustion mechanisms and to further develop gas turbine burners following the FLOX® concept. The combined results of all measurement techniques that have been applied to these two flames thus form a unique and comprehensive data set for the validation of numerical simulation models.

In this work, an atmospheric model combustion chamber was characterized employing Laser Vibrometry, chemiluminescence and Particle Image Velocimetry. The test object was a variable geometry burner enclosed with a liner, with the flame optically accessible through four fused silica windows. In this burner with adjustable flame conditions the cavity of the atmospheric model combustion chamber was excited at a frequency around 200Hz. Resonant and non-resonant flame conditions were investigated and compared by laser vibrometer interferometry, schlieren visualization and OH*/CH* chemiluminescence. Additionally, the velocity field was recorded with Particle Image Velocimetry, while the aerodynamics of the burner plenum was analyzed with Computational Fluid Dynamics.

For their application in a multisector combustor, several laser-based measurement techniques underwent further development to generate useful results in the demanding environment of highly luminous flames under elevated pressures. The techniques were applied to two burner configurations and the results were used to explain their respective behavior. Multisector combustors at elevated pressure present formidable difficulties to the operation of laser based techniques, as the optical path length is longer than for a single sector while the optical density of the flowing medium can be quite high. Hence, the techniques have to be set up to perform under low signal to noise levels. Nevertheless for a validation exercise geared at multidimensional simulation, quantitative results are requested. Here the modification of standard Laser Induced Incandescence as a means to measure soot concentrations with higher dynamic range is described. For situations where the optical density is too high for the application of imaging techniques, laser absorption was used and its application in the multisector combustor is presented. Since combustion and soot formation is closely coupled to flowfield and mixing, velocity measurements are highly desired for comparison with computed flowfields. Although with Laser-Doppler Anemometry a well-established technique is at hand, the high operating costs of a multisector combustor cannot be supported for the needed time of operation. Therefore an effort was made to make the Particle Imaging Velocimetry technique operable in highly luminous flames by using a second camera. The two-camera system and its operation are described in the paper. Finally the application on two different burner configurations is reported together with chemiluminescence as a tracer for heat release, and differences in soot production are related to the measured flow field.

In this work, results of comprehensive high-pressure tests and numerical simulations of high momentum jet flames in an optically accessible combustion chamber are presented. A generic single nozzle burner was designed as a full-scale representation of one duct of a high temperature FLOX® gas turbine combustor with a model pilot burner supporting the main nozzle. As an advanced step of the FLOX® gas turbine combustor development process, tests and simulations of the entire burner system (consisting of a multi nozzle main stage plus a pilot stage) are complemented with this work on an unscaled single nozzle combustor, thus supporting the development and testing of sub concepts and components like the mixing section and dual-fuel injectors. These injectors incorporate a gaseous fuel stage and a spray atomizer for liquid fuels, both separately exchangeable for testing of different fuel placement concepts. The combustor was successfully operated at gas turbine relevant conditions with natural gas including a variation of the Wobbe index, and with light heating oil with and without water admixture. The presented work is the first of two contributions and covers the description of the experimental setup, an overview of the numerical methods, high-pressure test results for different fuels and variations of the operating conditions including exhaust gas measurements and basic optical diagnostic methods, together with CFD results for several cases. The other part will present detailed and focused investigations of few conditions by complex and extensive optical and laser combustion diagnostics.

In this paper the development and the application of a numerical code suited for the simulation of gas-turbine combustion chambers is presented. In order to obtain an accurate and flexible framework, a finite-rate chemistry model is implemented, and transport equations for all species and enthalpy are solved. An assumed PDF approach takes effects of temperature and species turbulent fluctuations on the chemistry source term into account. In order to increase code stability and to overcome numerical stiffness due to the large-varying chemical kinetics timescales, an implicit and fully-coupled treatment of the species transport equations is chosen. Low-Mach number flow equations and k-ε turbulence model complete the framework, and make the code able to describe the most important physical phenomena which take place in gas-turbine combustion chambers. In order to validate the numerical simulations, experimental measurements are carried out on a generic non-premixed swirl-flame combustor, fuelled with syngas-air mixtures and studied using optical diagnostic techniques. The combustor is operated at atmospheric and high-pressure conditions with simulated syngas mixtures consisting of H2, N2, CH4, CO. The combustor is housed in an optically-accessible combustion chamber to facilitate the application of chemiluminescence imaging of OH* and planar laser-induced fluorescence (PLIF) of the OH-radical. To investigate the velocity field, particle image velocimetry (PIV) is used. The OH* chemiluminescence imaging is used to visualise the shape of the flame zone and the region of heat release. The OH-PLIF is used to identify reaction zones and regions of burnt gas. The fuel composition is modelled after a hydrogen-rich synthesis gas, which can result after gasification of lignite followed by a CO shift reaction and a sequestration of CO2. Actual gas compositions and boundary conditions are chosen so that it is possible to outline differences and similarities among fuels, and at the same time conclusions about flame stability and combustion efficiency can be drawn. A comparison between experimental and numerical data is presented, and main strengths and deficiencies of the numerical modelling are discussed.

Lean premixed dry low emission (DLE) combustion system in a gas turbine engine is a globally accepted concept to reduce pollutant emissions and to improve combustion efficiency. This study is focused on an industrial downscaled prototype burner (4th Generation Dry Low Emission Burner for SGT-750 designed and manufactured by Siemens Industrial Turbo machinery AB), which has been tested extensively at atmospheric conditions. To enhance the operability and alleviate flame dynamics behavior, multiple fuel and air circuits (i.e. Rich-Pilot-Lean (RPL), Pilot and Main) are engaged in the burner. Primarily, present study evaluates the RPL-Pilot interaction effect on the main combustion zone. A highly swirled flow from the burner exit produces a central recirculation zones (CRZ) to recirculate the hot vitiated gas for sustaining the combustion process. The main flame is stabilized in the inner shear layer (ISL), which is found in the diverging section (named as Quarl). The total power of the burner was varied between 70–140 kW and the fuel used for the experiment was 99.5% pure methane. A short length quartz liner was used for the experiment and the residence time of the combustor is 9 ms. At the liner exit, emission sampling (CO, NOx) has been conducted using a water-cooled emission probe. Optical measurements were permitted, as the Quarl and combustor liner were optically accessible. Planar laser-induced fluorescence of OH molecule (OH-PLIF) and natural chemiluminescence measurements were conducted to visualize the flame characteristics and its response by changing the RPL and Pilot fuel splits. A comprehensive study was performed by varying the RPL residence time to investigate the main flame stabilization and pollutant formation of the burner. Higher RPL residence time exhibits NOx benefits but at the same time flame instability was increased. Pilot fuel percentage modification demonstrate negative impact on NOx formation due to the limited mixing of fuel and air. With the increase of Pilot fuel split, CO emission decreases, which is advantageous for increasing the LBO margin. The study has identified a number of critical situations where the flame was stabilized without any RPL and Pilot combustion. Apart from the experimental results, a simple reactor network model has been applied for predicting NOx emission. Different kinetic mechanisms were assessed and the prediction results are compared to experimental results. Heat loss from the combustor wall played a significant role on emission formation and was included in the reactor model. This study provides a good understanding of the new DLE industrial burner concept and the RPL-pilot interaction effect on the emission.

A model FLOX® combustor, featuring a single high momentum premixed jet flame, has been investigated using laser diagnostics in an optically accessible combustion chamber at a pressure of 8 bar. The model combustor was designed as a large single eccentric nozzle main burner (Ø 40 mm) together with an adjoining pilot burner and was operated with natural gas. To gain insight into the flame stabilization mechanisms with and without piloting, simultaneous Particle Image Velocimetry (PIV) and OH Laser Induced Fluorescence (LIF) measurements have been performed at numerous two-dimensional sections of the flame. Additional OH-LIF measurements without PIV-particles were analyzed quantitatively resulting in absolute OH concentrations and temperature fields. The flow field looks rather similar for both the unpiloted and the piloted case, featuring a large recirculation zone next to the high momentum jet. However, flame shape and position change drastically. For the unpiloted case, the flame is lifted, widely distributed and isolated flame kernels are found at the flame root in the vicinity of small scale vortices. For the piloted flame, on the other hand, both pilot and main flame are attached to the burner base plate, and flame stabilization seems to take place on much smaller spatial scales with a connected flame front and no isolated flame kernels. The single shot analysis gives rise to the assumption that for the unpiloted case small scale vortices act like the pilot burner flow in the opposed case and constantly impinge and ignite the high momentum jet at its root.

Multiple, interacting flames in DLE systems can increase flame surface area and promote mixing of hot-products into the reactants — leading to an efficient usage of combustion volume and improved injector performance. An optically-accessible, confined, linear array of five swirl nozzles was recently built [1] to investigate flame dynamics and validate computational strategies. The present work focuses on modeling a dataset representative of lean gas turbine conditions, using a flamelet approach. A preheated (500K), premixed fuel-air mixture (ϕ = 0.55, Tflame = 1732K) at atmospheric pressure was injected through the swirlers at 40 m/s into a rectangular chamber. High-speed laser measurements of the flow (3 component velocity field from 10 kHz stereoscopic particle image velocimetry (S-PIV)) and flame (planar laser induced fluorescence of the hydroxyl radical (OH-PLIF)) were used for model validation. The objectives of this work: (1) Evaluate a flamelet-progress variable method based on flamelet-generated manifolds (FGM) and examine its sensitivity to models for micro (scalar dissipation) and large scale mixing (anisotropic RANS vs LES) and (2) Obtain insight into the velocity field and flame stabilization in an interacting system. Computations indicate that high-swirl nozzles produce bluff-body flames anchored to shear-layer vortices due to an arrested flow expansion. The anisotropic RANS turbulence model under-predicts the recirculation zone strength but predicts flow development and Reynolds stress profiles fairly well. While LES is more accurate overall, both models over-predict flow fluctuations in the transitional flow at the end of the recirculation bubble where flow becomes axially positive. The flamelet approach predicts the flame-shape and length correctly but over-predicts the reaction rate in-between swirlers. The effect of including a reactive SDR model is to significantly increase flame-flow interaction (higher scalar variance) but does not appear to influence the overall shape or location of the flame.

In support of the development of CFD for aeroengine combustion, quantitative measurements of spray properties and temperature were made. A generic swirling air blast injector was designed and built to produce well defined inlet conditions and for ease of numerical description for the CFD development. The measurements were performed in an optically accessible single sector combustor at pressures of 4 and 10 bar and preheat temperatures of 550 and 650 K, respectively. Jet A-1 was used as fuel. The burner air to fuel ratio was 20 and the pressure loss was set to 3%. Sauter mean diameter (SMD) profiles and liquid mass flux distributions were generated from the phase Doppler anemometry (PDA) measurements of the evaporating spray drop sizes and velocities. With planar measurements of Mie scattering and kerosene-LIF, the distribution of kerosene (liquid and vapor phase) was imaged. Temperatures were measured with OH-LIF. The burner was designed with a straight outlet to exhibit lifted flames. Hence initial distributions of size, velocity and density of the spray were measured before it entered the flame. Almost complete prevaporization was seen at least for the 4 bar flame. Compared with atmospheric investigations, the smaller diameters of the droplets and the small streamline curvature of the configuration led to a more uniform behavior of the spray.