Literatura científica selecionada sobre o tema "Rich-Quick Quench-Lean (RQL)"

Combustion tests on SiC/SiC CMC components were performed in an aircraft combustion environment using the rich-burn, quick-quench, lean-burn (RQL) sector rig. SiC/SiC fasteners were used to attach several of these components to the metallic rig structure. The effect of combustion exposure on the fastener material was characterized via microstructural examination. Fasteners were also destructively tested, after combustion exposure, and the failure loads of fasteners exposed in the sector rig were compared to those of as-manufactured fasteners. Combustion exposure reduced the average fastener failure load by 50% relative to the as-manufactured fasteners for exposure times ranging from 50 to 260 hours. The fasteners exposed in the combustion environment demonstrated failure loads that varied with failure mode. Fasteners that had the highest average failure load, failed in the same manner as the unexposed fasteners.

To determine the flow field structure and flow characteristics of a rich-quench-lean (RQL) combustor-combined low-emission and high-temperature rise combustion, a two-dimensional PIV technology was used to evaluate the effect of aerodynamic and structural parameters on the flow field and flow characteristics of the combustor. The variation in the total pressure loss of the combustor has little effect on the flow field structure of the combustor. However, the variation in the parameters of primary holes significantly affects the structure of the central recirculation zone, the distribution of local recirculation zones in the rich-burn zone and quenching zone, and the average residence time in the quenching zone. On the plane that passes through the center of the primary hole, the variations in the array mode and diameter of primary holes would form entrainment vortexes with different characteristics, thus affecting the position and flow state of local recirculation in the rich-burn zone and the local structure of the central recirculation zone. As the rotational direction of local recirculation coincides with that of the main air flow in the primary zone, the local center recirculation is intensified. In contrast, it is weakened. As the primary holes are located at half height (H/2) of the combustor, the residence time of air flow at the quenching zone can be shortened by 65% through using the staggered structure of primary holes and increasing the momentum of the partial single-hole jet. The quick-mixing process in the quenching zone is not beneficial to increase the number of primary holes and decrease the momentum of the single-hole jet.

A combustion chamber, as one of the crucial GTE components, plays a significant role in ensuring its environmental characteristics. Therefore, understanding the mechanisms of forming harmful substances (pollutants) and a possibility to predict their emission values, when changing the engine operation parameters and the external conditions, are some of the key issues to ensure ICAO (International Civil Aviation Organization) standards. The solution of these issues allows us to estimate the emission characteristics at the stage of engine design and to develop effective methods for preventing the formation of air pollutants, as well as to increase the efficiency of burning fuels. Since the first limitation introduced by the Committee on Aviation Environmental Protection (CAEP / 1) in 1986 there were several amendments. The (CAEP / 8) standard, which has come into force since January 1, 2014, is already being ready to be replaced by more stringent requirements, i.e. reducing emissions of nitrogen oxides (NOx) by 40% by 2020 (as compared to the (CAEP / 2). As to other pollutants (CO, HC, SN), the trend is similar.Main difficulties in creating combustion chambers with low-emission pollutants arise from the fact that reducing CO and NOx requires mutually opposite measures. A rational combustion chamber design should represent some trade-off between the requirements arising from the task of reducing emissions of these two groups of polluting components. This can be achieved through improving operation of the primary, burnout, and mixing zones, rationally chosen volume of the flame tube (FT), and residence time in the combustion chamber.To have a clearer idea of possible ways to reduce pollutant emission of the GTE combustion chamber, it is necessary to take into account the basic mechanisms of their formation.The main methods of reducing CO emission are based on the physical-and-chemical patterns of its formation:Supporting the mixture composition in the combustion zone to be closer to α = 1.1 ... 1.3;Increasing the combustion zone volume and the residence time in it.The above methods of reducing CO emissions are difficult to implement in low-emission combustion chambers because their using leads to the sharp increase of NOх formation. It is found that only in a very narrow temperature range (flame temperature Тпл = 1650 ... 1900 K) desirable levels of NOх and CO emissions can be simultaneously achieved.To reduce the level of NOх emission, are used the following approaches:- liquid fuel combustion implemented at a small length of FT with a residence time in the high temperature zone (over 1920 K) 5 ... 6 milliseconds followed by intensive quench in the mixing zone, that is, the principle of "quick burn and quick quench» is used;- fuel combustion at the temperature of 1750 ± 50 K (i.e. below 1920 K), with an outlet temperature pattern formed through the air feed in the mixing zone or- from the zone of a combustion chamber flame tube head with no quench of product of combustion.The analytical results of a total scope of developments in reducing pollutant emissions allow us to distinguish the following standard fuel combustion technologies in GTE combustion chambers, which meet the available environmental requirements:1) use of burning the lean pre-mixed fuel in "dry" combustion chambers (This technology process uses the following schemes: RQL (Rich-Quench-Lean) – rich mixture combustion, followed by rapid air blending and lean mixture afterburning; LPP (Lean Premixed Pre-vaporized) - combustion of a lean premixed and vaporized mixture; LDI (Lean Direct-Injection) - combustion with lean mixture injection directly into the combustion zone;2) catalytic combustion of a fuel-air mixture;3) use of "wet" combustion chambers with diffusion flame and water injection (steam);4) additional use of catalytic cleaning of GTP outlet gases.At present, natural gas combustion chambers with emission of NOx and CO <10ppm are under design. This is almost the lowest achievable level for the operating conditions under consideration. In designing such combustion chambers a main task is to develop and improve methods that allow calculating the combustion kinetics of a gas mixture, improving the software systems for calculating and obtaining reliable data on emission of harmful substances, and also to develop experimental methods for creating and full-scale engineering of the low-emission combustion chambers for stationary units and advanced aircraft engines. The presented methods for reducing emission of harmful substances, namely improving techniques to feed fuel, zone arrangement of combustion, use of catalysts in the combustion chamber and at the outlet of the plant, when used, should result not only to reducing emissions, but also to improving the other important combustion chamber characteristics, especially extension of steady combustion limits. Studies to obtain ultra-low emission levels, based on the burning concept of the lean homogeneous mixture in the combustion chamber, are at an early stage. It is necessary to solve a number of important problems, such as a problem of «lean» flameout, of flash back, and also ensuring a sufficient evaporation of fuel and its mixing with air.

Abstract In this paper, we present combustor acoustics in a high-pressure liquid-fueled Rich burn - Quick quench - Lean burn (RQL) styled swirl combustor with two separate fuel circuits. The fuel circuits are the primary (which has a pressure atomizer nozzle) and secondary (which has an air blast type nozzle) circuits. The data were acquired during two dynamical regimes - combustion noise, where there is an absence of large amplitude oscillations during the unsteady combustion process, and intermittency, where there are intermittent bursts of high amplitude oscillations that appear in a near-random fashion amidst regions of aperiodic low amplitude fluctuations.?This dynamic transition from combustion noise to combustion intermittency is investigated experimentally by systematically varying the fuel equivalence ratio and primary-secondary fuel splits. Typical measures such as the amplitude of oscillations cannot serve as a measure of change in the dynamics from combustion noise to intermittency due to the highly turbulent nature. Hence, recurrence plots and complex networks are used to understand the differences in the combustor acoustics and velocity data during the two different regimes.?We observe that the combustor transitions from stable operation to intermittency when the equivalence ratio is increased for a given primary fuel flow rate and conversely when the percentage secondary fuel flow rate is increased for a given equivalence ratio. The contribution of this work is to demonstrate methodologies to detect combustion instability boundaries when approaching them from the stable side in highly turbulent, noisy combustors.

Les effets anthropogéniques sur l’environnement posent un défi majeur pour l’industrie aéronautique. Des réglementations de plus en plus strictes et la nécessité de rendre le transport aérien durable orientent les recherches actuelles vers des systèmes propulsifs innovants. Dans ce contexte, Safran Helicopter Engines développe sa technologie brevetée de combustion giratoire (SCT), visant à améliorer les performances des moteurs d’hélicoptères. Déjà implémentée sur le moteur Arrano, cette technologie est davantage optimisée pour réduire significativement les émissions de NOx et de suies. Dans le cadre du programme européen LOOPS, deux nouveaux systèmes d’injection de carburant sont étudiés : l’un conçu pour un régime riche dans une chambre RQL, et l’autre pour une combustion pauvre. Cette thèse évalue expérimentalement ces systèmes à l’aide de diagnostics laser avancés, adaptés aux environnements réactifs à haute pression. Le banc HERON, développé au CORIA, permet d’analyser leurs performances de combustion et évaluer les émissions dans des conditions représentatives des moteurs d’hélicoptères : pressions de 8 à 14 bar, températures d’entrée d’air de 570 à 750 K, et richesses de 0,6 à 1,67. Des diagrammes de stabilité de flamme sont établis, suivis d’analyses des propriétés du spray liquide par PDPA (Phase Doppler Particle Anemometry). Les champs aérodynamiques sont mesurés en conditions réactive et non-réactive par PIV (Particle Imaging Velocimetry) ultra-rapide à 10 kHz. La structure des flammes est caractérisée par PLIF-OH, tandis que la PLIF-kérosène permet d’étudier l’évaporation du carburant en détectant les mono- et di- aromatiques. Les diagnostics couplés simultanément PLIF-NO, PLIF-OH et PLIF-kérosène corrèlent les structures des flammes, les distributions des phases liquide et vapeur, et les zones de formation de NO. De même manière, la PLII (Planar Laser-Induced Incandescence) couplé avec PLIF-OH, PLIF-kérosène permets d’analyser les mécanismes de formation et d’oxydation des suies. Des méthodes spécifiques déterminent des distributions 2D des concentrations de NO, OH et des fractions volumiques de suies. Les résultats montrent une flamme asymétrique pour l’injecteur riche, avec une efficacité de combustion élevé dans la partie supérieure grâce à une injection liquide augmenté localement. Malgré des richesses élevées, les niveaux de suies restent modérés, tandis que le NO se forme principalement près de la flamme, confirmant le mécanisme thermique de Zeldovich. L’injecteur en régime pauvre présente une structure de flamme typique des flammes swirlées stratifiées, malgré la légère asymétrique. Une meilleure évaporation du carburant y favorise une combustion plus efficace, réduisant la longueur de flamme et les NO, grâce à des températures de flamme plus basses. Cependant, des niveaux modérés de suies sont également observés malgré le régime pauvre. Les conditions opératoires influencent fortement les performances. À haute pression, l’atomisation du spray est accélérée, l’angle d’expansion du spray augmente, et les zones de recirculation interne sont renforcées, modifiant la structure des flammes. L’augmentation des émissions de suies par la haute pression est observée pour l’injecteur en régime riche, gardant une richesse constante sur l’ensemble des conditions testées, tandis que les niveaux de NO restent stables. Pour l’injecteur en régime pauvre, les conditions réactives avec une richesse minimale à haute pression atténuent les effets de la pression, stabilisant la production de suies tout en réduisant les concentrations de NO. Ces résultats mettent en évidence le potentiel des deux systèmes d’injection pour optimiser les performances tout en réduisant les émissions des futurs moteurs d’hélicoptères
Anthropogenic effects on the environment present a major challenge for the aeronautical industry. Increasingly stringent pollution regulations and the necessity for sustainable air transport are driving the nowadays research toward innovative propulsion systems. In this context, Safran Helicopter Engines is advancing its patented Spinning Combustion Technology (SCT), aimed at improving helicopter engine performance. Already implemented in the Arrano engine, SCT is now being refined to significantly reduce NOx and soot emissions. As part of the European LOOPS program, two novel fuel injection systems are under investigation: one operating in a rich combustion regime tailored for an RQL combustion chamber and the other designed for lean combustion. The scientific activity of this thesis focuses on the experimental characterization of these injection systems using state-of-the-art laser diagnostics optimized for high-pressure reactive environments. The HERON combustion facility at CORIA enables the analysis of combustion and pollutant performance under conditions representative of helicopter engines, with pressures from 8 to 14 bar, air inlet temperatures from 570 to 750 K, and equivalence ratios ranging from 0.6 to 1.67. Initial flame stability maps are established, followed by in-depth analyses of liquid spray properties using Phase Doppler Particle Anemometry (PDPA). High-speed Particle Imaging Velocimetry (PIV) captures aerodynamic fields under reactive and non-reactive conditions at 10 kHz. Flame structures are examined via OH-PLIF fluorescence imaging, while kerosene-PLIF evaluates liquid and vapor fuel distributions, particularly probing aromatic components in Jet A-1 kerosene. Furthermore, NO-PLIF imaging, combined with OH-PLIF and kerosene-PLIF, enables spatial correlations between flame structure, fuel distribution, and NO production zones. Soot formation and oxidation mechanisms are explored through Planar Laser-Induced Incandescence Imaging (PLII), integrated with OH-PLIF and kerosene-PLIF. Specific methods are developed to obtain 2D distributions of quantitative concentrations of NO, OH and soot volume fraction. Results reveal that the rich-burn injector produces an asymmetrical flame with enhanced upper-zone combustion efficiency due to locally intensified liquid fuel injection. Moderate soot levels are observed despite high equivalence ratios, while localized NO production, primarily near the flame, is attributed to the Zeldovich thermal mechanism. Conversely, the lean-burn injector forms a flame structure characteristic of stratified swirl flames, despite the minor asymmetry. Improved fuel evaporation leads to higher combustion efficiency, shorter flame lengths, and a reduction in NO formation, attributed to lower flame temperatures. In spite of the lean combustion conditions, moderate soot levels are measured for the second injector. Operating conditions strongly influence performance. Higher pressures accelerate spray atomization, increase spray expansion angles, and strengthen internal recirculation zones, reshaping flame structures. The increase in soot production at higher pressure is particularly demonstrated by the rich-burn injector due to constant equivalence ratios across all test conditions, while NO levels remain stable. For the lean-burn injector, leaner operation at elevated pressures moderates pressure effects, maintaining consistent soot levels and reducing NO concentrations. These findings highlight the potential of both injection systems for optimizing performance and reducing emissions in future helicopter engines

RQL (Rich-burn/Quick-quench/Lean-burn) is a candidate to support fuel flexible stationary power generation. The equivalence ratio of rich-burn zone (Φr) and the quench air flow are paramount for implantation of the whole process. In this paper, an experimental test stand with multi-sector model combustor was established. Rich premixed combustion were used in rich zone. The experiments which pay attention to the impacts of Φr and quench air flow on the combustion performance and emission are conducted. The results show that the flame in RQL combustor is segmented when Φr >1.4, presenting flameless combustion in rich zone and a pale blue flame in lean zone. Axial temperature distribution is M-type. Two peaks appear at the head and tail of the combustion chamber, and the valley is located in the quench zone. The concentration of CO decreases rapidly in quench zone because of the injection of quench air. However, the concentration of NOx increases quickly at the same time. The outlet emissions of CO and NOx in RQL combustor are maintained at low level (<20ppm@15%O2). With a decrease of Φr from 1.4 to 1.2, the emission of NOx increases, and the emission of CO decreases. With jet-to-mainstream mass-flow ratio increases from 1.28 to 2.22., the concentration of NOx in outlet declines gently, but the CO emission increase. The average exhaust temperature depresses gradually, and the uniformity coefficient of exhaust temperature increases.

Abstract Swirl-stabilized, turbulent, non-premixed kerosene-air flames were studied experimentally in an RQL (Rich burn/Quick-quench/Lean-burn) model combustor equipped with large optical accesses. The goal of these studies was to characterize the flame topology as well as soot and NO formation processes in the rich primary zone of the RQL combustor, and to establish a large database for future validation of numerical simulations. The experiments were performed under relevant operating conditions up to 4.5 bar. The aerodynamic flow field was measured by Particle Image Velocimetry, the flame structure, fuel and NO distributions by Planar Laser-induced Fluorescence and soot volume fractions by Planar Laser-induced Incandescence. Additional measurements were performed by a scanning mobility particle sizer technique to record the number of soot particles per unit volume as well as the particles size. Two equivalence ratio conditions were used to study the impact of relevant scalar parameters on NO and soot production. For each condition, instantaneous and average distributions of the measured parameters are presented and discussed. The coupling of the optical and intrusive measurement techniques has finally enabled to highlight the impact of the liquid and gas phases fuel distribution on the flame structure, but also on NO and soot formation.

The injection of jets normal to a crossflow is a key technology for the development of an advanced low NOx gas turbine based on a Rich-Burn/Quick-Quench/Lean-Burn (RQL) combustor. The RQL combustor depends on an efficient quick mix section that rapidly and uniformly dilutes the rich zone products to minimize emissions. Therefore, an experimental investigation of a non-reacting mixing process of jets in a crossflow was conducted. The jets were perpendicularly injected through one stage of opposed rows of circular orifices into a slightly heated crossflow within a rectangular duct. All geometries were tested with staggered arrangements of the centerlines of the opposed jets. The temperature distribution was measured and from that the mixing rate was determined for parametric variations of flow and geometric conditions. In accordance with the application to RQL-combustion, emphasis was put on high momentum flux ratios with high massflow addition. The experimental study provides the data base for a correlation of best mixing depending on geometric conditions for staggered mixing configurations. The correlation presented specifies the optimum momentum flux ratio as a function of the duct height to hole diameter ratio and the relative spacing of the injected jets.

Abstract This paper presents data collected from a model rich-burn, quick-quench, lean-burn swirl-injected single sector combustor. This is part of a larger effort to study the dynamics behind direct and indirect sources of combustor noise. Simultaneous acoustic pressure and OH* chemiluminescence were obtained over a range of conditions, particularly focusing upon the effect of air splits and fuel flow rates upon the broadband acoustic response. Acoustic pressure and chemiluminescence spectra were analyzed and coherence and correlation areas were estimated. Results demonstrate that the equivalence ratio at the primary zone has a significant impact on the frequency response. Higher equivalence ratios led to lower, low frequency broadband noise below 300 Hz but excited a narrowband mode at approximately 650 Hz. Differing the primary and secondary air split ratio but keeping the primary zone equivalence ratio constant showed no significant effect on the broadband noise. The chemiluminescence and acoustic signals showed weak coherence at all frequencies.

A series of experimental researches, including ignition and combustion tests at atmospheric pressure conditions, were conducted to develop a combustor for a small class aircraft engine (with pressure ratio about 20). Under restrictions of the combustor size and cost, in order to satisfy the requirement for ignition and blowout performance with sufficient combustion efficiency and NOx reduction for wide range of operating conditions, we applied single fuel nozzles and utilized the rich-burn-quick quench-lean-burn (RQL) combustion approach. Preliminary combustion tests were conducted to optimize the ignition and blowout characteristics, approximately determining positions of air holes and igniter, and selecting fuel nozzle parameters. Consequently, tubular combustor tests with exhaust gas analysis were also conducted to optimize the air mass flow ratio and the air holes’ positions to suppress NOx emissions. Obtained results showing the RQL characteristics of the combustion, decreasing NOx emissions at high equivalence ratio range, are presented in this report, and the optimized air mass flow ratio and position of air holes, which will be applied to a single sector combustor for the testing at practical pressure and temperature conditions, are also presented.

The modern low emissions gas turbines operate under some of the most challenging operating conditions as more demands are exercised on their performance. For example, the future engines will have higher thrust-to-weight ratio, improved fuel efficiencies, and high overall pressure ratios. Furthermore, the environmental safety needs will dictate many of the future low emissions combustor designs to be either Lean-Premixed (LP), Lean Direct Injection (LDi), Rich-burn-Quick quench-Lean burn (RQL) or catalytic. These will impose additional demands on developing unique high temperature materials that can survive in oxidizing and reducing environments, under high temperature and pressure conditions, and have other material properties such as superior strength and stiffness. In this paper, first we discuss the salient features of advanced low-emissions gas turbines and their needs for unique material technology development. Next, we discuss the state-of-the-art material technology development as it is applied to current gas turbines. And, finally we review the material developments that will be needed for the future gas turbine engines.

Combustion tests on SiC/SiC CMC components were performed in an aircraft combustion environment using the Rich-burn, Quick-quench, Lean-burn (RQL) sector rig. SiC/SiC fasteners were used to attach several of these components to the metallic rig structure. The effect of combustion exposure on the fastener material was characterized via microstructural examination. Fasteners were also destructively tested, after combustion exposure, and the failure loads of fasteners exposed in the sector rig were compared to those of as-manufactured fasteners. Combustion exposure reduced the average fastener failure load by 50% relative to the as-manufactured fasteners for exposure times ranging from 50 to 260 hours. The fasteners exposed in the combustion environment demonstrated failure loads that varied with failure mode. Fasteners that had the highest average failure load, failed in the same manner as the unexposed fasteners.

A series of research experiments under practical conditions has been conducted to develop a combustor for a small-class aircraft engine (with the pressure ratio of about 20). In the previous research experiments, including ignition and emission tests under atmospheric pressure, we applied a single airblast fuel nozzle and utilized the rich-burn quick-quench lean-burn (RQL) combustion approach. The combustor was tuned to show the behavior of the RQL under the atmospheric condition. In this paper, the results of single-sector combustor experiments under the practical temperature and pressure conditions are presented, in which RQL behavior is observed and NOx emissions in the ICAO (International Civil Aviation Organization) LTO (Landing and Take-Off) cycle are reduced to 45% of the ICAO CAEP4 (Committee on Aviation Environmental Protection 4) standard. Also the results of successive multi-sector combustor tests to optimize combustion performances with a more practical combustor configuration under the practical conditions are presented. The emission characteristics which are obtained are compared with those of the single-sector tests, and combustor size and configuration, air mass flow ratio and air hole positions are tuned through a series of multi-sector experiments. After the optimization, the combustor achieved the following performances; NOx emissions are reduced to less than 42% of the ICAO CAEP4 standard, CO and THC (Total Hydrocarbon) are reduced to those of 2% and 50% respectively, the lean blowout limit is kept over 220 AFR (Air to Fuel Ratio) at the idle condition and the exit temperature profile at the full load condition is sufficiently uniform (P.T.F.&lt;0.15). The process of optimization will be discussed in this report.

Abstract This paper presents measurements of 10 kHz acetone planar laser induced fluorescence (PLIF) to study the behavior of effusion cooling fluid injected into a non-reacting gas turbine combustor flow at elevated pressure. This study was performed as part of a larger effort to understand potential interactions of the swirling flame with the cooling air. The combustor — which was representative of a rich-burn/quick-quench/lean-burn (RQL) configuration — consisted of a swirl nozzle, quench jets, and a modular liner that could be fitted with various effusion cooling panels and optical access windows. Primary air was seeded with acetone, and passed through the swirl nozzle. Unseeded secondary air was passed on the outside of the liner, entering the combustion chamber through the quench jets and effusion panels. The PLIF laser sheet was arranged parallel to the effusion panel at various offset distances to visualize the mixing between the core flow and effusion jets. The PLIF images were analyzed with a POD-based methodology to de-noise the images and identify patterns in the effusion jet characteristics. The results show that high blowing ratios produce individual effusion jets rather than a single, coalesced film. The effusion jets are highly unsteady, interacting strongly with the turbulent flow from the swirl nozzle and dilution jets. Furthermore, the average trajectories of effusion jets are non-uniform across the panel and are shaped by upstream features in the combustor, namely swirl and dilution jets.