Browsing by Author "Sun, Xiaoxiao"
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Item Open Access A review of hydrogen micromix combustion technologies for gas turbine applications(Elsevier, 2025-05-13) Singh, Gaurav; Schreiner, B. Deneys J.; Sun, Xiaoxiao; Sethi, VishalHydrogen micromix combustion is a promising technology for gas turbines, introducing rapid, miniaturized air-fuel mixing, significantly reducing combustion zone length and nitrogen oxides (NOx) emissions. This review evaluates the state-of-the-art hydrogen micromix combustion technologies, focusing on injector performance, flashback characteristics, and NOx reduction strategies. Injector designs are categorized based on premixing and flame stabilization techniques. While stationary gas turbines approach Technology Readiness Level (TRL) 9, aviation applications remain below TRL 4. This review identifies key design principles and predictive modelling challenges and presents a development roadmap for advancing hydrogen micromix combustion technology for aviation from TRL 4 to TRL 9 by 2040.Item Embargo Application of CFD zooming for preliminary design of a low emissions combustor.(2018-10) Sun, Xiaoxiao; Sethi, Vishal; Li, YiguangThe design of low emissions combustors is particularly challenging as there is a requirement to deliver designs that meet a large number of performance, emissions and operability (often conflicting) objectives. There is an increasing need for combustor preliminary design and performance tools which can be used in the early phases of the design process for rapid design space exploration thereby reducing the risk and cost in the long term. Although both reduced order models and higher fidelity tools have been widely used for preliminary design independently, significant benefit can be derived from using a multi-fidelity modelling approach to address the limitation of reduced order model (accuracy) and high fidelity CFD (time and cost). To the author’s best knowledge there is no information in the public domain related to the coupling of reduced order models with higher fidelity 3D CFD multi-fidelity modelling tools for low emissions gas turbine combustion systems. Such a tool has a potential to offer a good compromise between modelling accuracy and computational expense. In this PhD research, a novel multi-fidelity zooming combustor preliminary design method is proposed. The method uses design outcomes of an existing reduced order model based design tool to construct CFD models for a series of RANS simulations. A case study for the design of a Lean Direct Injection Partially Premixed combustor was conducted to identify the limitations of an existing reduced order modelling approach. Dedicated CFD simulations were performed to demonstrate that improved methods/models/correlations can be derived from these higher fidelity simulations to refine the existing reduced order model. The main research contributions are summarised below: External aerodynamics – Performance is sensitive to inlet velocity profiles, the effect of which cannot be reflected in ROMs, realistic compressor outlet profiles is needed instead of generic turbulent pipe flow profiles. – Performance maps were generated from CFD which include more degrees of freedom and suggest a different ‘optimum locus’ than 1D correlations. Fuel injector initial conditions – The Sauter Mean Diameter calculated from correlations in the ROM is not suitable to be used as injection initial condition. Detailed correlations on jet breakup were used to generate representative droplet size and velocity for different nozzle designs and conditions. – Swirler flow split correlations does not account for flow turning in the venturi and the pre-mixer, coarse mesh CFD was sufficient to generate more accurate flow splits among different stages. Reacting flow – The initial 10 fuel nozzle ports design from the ROM was not sufficient for good mixing quality at the main stage, which resulted in higher flame temperature. The number was increased to 16, which provides more uniform flame distribution at the circumferential direction. – Three of the four methods used to generate the time delay provides consistent results. The time delay was used as an input of the ROM thermoacoustic analysis model. – The reactor layout can be better customised for emissions prediction with extra zones within the pilot injector and the dilution zone to account for reaction and recirculation. – Combustor cooling design was refined without modifying the variables of ROM, in which circumferential distribution was not captured. Simplified re-fining method was developed at less computational expense compared to complete Conjugate Heat Transfer simulations with the radiation model. Based on these findings, the reduced order design tool could be refined once the data from all parametric study cases are extracted and incorporated in the model, which is recommended as the future development of the work. The CFD model constructed could also be used to initiate higher fidelity Large Eddy Simulation.Item Open Access Characterising hydrogen micromix flames: combustion model calibration and evaluation(American Society of Mechanical Engineers, 2021-01-11) López-Juárez, Marcos; Sun, Xiaoxiao; Sethi, Bobby; Gauthier, Pierre Q.; Abbott, DavidHydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. The ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3. The micromix combustor comprises thousands of small diffusion flames for which air and fuel are mixed in a cross-flow pattern. This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and low-temperature small diffusion flames in lean overall equivalence ratios. For hydrogen-air mixtures there is a need to further characterise the physical importance and calibration process of the laminar Schmidt (Sc), Lewis (Le) and Prandtl (Pr) and turbulent Schmidt (Sc) numbers. In addition, there is limited numerical and experimental data about flame characteristics and emissions of hydrogen micromix combustor at high pressure and temperature conditions. In this paper, the CFD software STAR-CCM+ was used with the FGM (Kinetic Rate) combustion model to simulate and calibrate hydrogen micromix flames. The research was divided into two parts. In the first part, the values of laminar Schmidt, Lewis and Prandtl numbers for H2 and air, non-reactive, flow mixtures were estimated as 0.22, 0.3 and 0.75 from correlations obtained in the literature. The typical Borghi diagram has been modified to represent this type of diffusion flame, since the assumption of Sc = Le = Pr = 1 can not be applied to hydrogen micromix flames and it is only for premixed flames. This diagram characterizes flame regime based on Damköhler (Da), Karlovitz (Ka) and turbulent Reynolds (Ret) numbers that were calculated from preliminary CFD simulations. In the second part, the value of laminar Schmidt number was set as constant while laminar Lewis and Prandtl numbers were obtained from the flamelet tables. A Turbulent Schmidt number was then obtained by comparing RANS and LES simulations of a single injector. If Sct > 0.2, the predicted NOx production of RANS simulations approaches that of LES; while Sct < 0.2 provides similar overall flame structure between RANS and LES. It is concluded that, for the current simulations, Sct = 0.2 is a good compromise between flame structure and emissions prediction. Flame characteristics and NOx emissions given by Thickened Flame and FGM Kinetic Rate models in a single injector geometry were also compared.Item Open Access A comparative analysis of different hydrogen production methods and their environmental impact(MDPI, 2023-11-29) Nnabuife, Somtochukwu Godfrey; Darko, Caleb Kwasi; Obiako, Precious Chineze; Kuang, Boyu; Sun, Xiaoxiao; Jenkins, Karl W.This study emphasises the growing relevance of hydrogen as a green energy source in meeting the growing need for sustainable energy solutions. It foregrounds the importance of assessing the environmental consequences of hydrogen-generating processes for their long-term viability. The article compares several hydrogen production processes in terms of scalability, cost-effectiveness, and technical improvements. It also investigates the environmental effects of each approach, considering crucial elements such as greenhouse gas emissions, water use, land needs, and waste creation. Different industrial techniques have distinct environmental consequences. While steam methane reforming is cost-effective and has a high production capacity, it is coupled with large carbon emissions. Electrolysis, a technology that uses renewable resources, is appealing but requires a lot of energy. Thermochemical and biomass gasification processes show promise for long-term hydrogen generation, but further technological advancement is required. The research investigates techniques for improving the environmental friendliness of hydrogen generation through the use of renewable energy sources. Its ultimate purpose is to offer readers a thorough awareness of the environmental effects of various hydrogen generation strategies, allowing them to make educated judgements about ecologically friendly ways. It can ease the transition to a cleaner hydrogen-powered economy by considering both technological feasibility and environmental issues, enabling a more ecologically conscious and climate-friendly energy landscape.Item Open Access Comparison of hydrogen micromix flame transfer functions determined using RANS and LES(ASME, 2019-11-05) McClure, Jonathan; Abbott, David; Agarwal, Parash; Sun, Xiaoxiao; Babazzi, Giulia; Sethi, Vishal; Gauthier, Pierre Q.Hydrogen has been proposed as an alternative fuel to meet long term emissions and sustainability targets, however due to the characteristics of hydrogen significant modifications to the combustion system are required. The micromix concept utilises a large number of miniaturised diffusion flames to improve mixing, removing the potential for local stoichiometric pockets, flash-back and autoignition. No publicly available studies have yet investigated the thermoacoustic stability of these combustion systems, however due to similarities with lean-premixed combustors which have suffered significant thermoacoustic issues, this risk should not be neglected. Two approaches have been investigated for estimating flame response to acoustic excitations of a single hydrogen micromix injector element. The first uses analytical expressions for the flame transfer function with constants obtained from RANS CFD while the second determines the flame transfer function directly using unsteady LES CFD. Results show the typical form of the flame transfer function but suggest micromix combustors may be more susceptible to higher frequency instabilities than conventional combustion systems. Additionally, the flame transfer function estimated using RANS CFD is broadly similar to that of the LES approach, therefore this may be suitable for use as a preliminary design tool due to its relatively low computational expense.Item Open Access Comparison of tabulated and complex chemistry turbulent-chemistry interaction models with high fidelity large eddy simulations on hydrogen flames(American Society of Mechanical Engineers, 2021-01-11) Zghal, M.; Sun, Xiaoxiao; Gauthier, Pierre Q.; Sethi, VishalHydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. The EU H2020 ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3. The micromix combustor comprises thousands of small diffusion flames where air and fuel are mixed in a crossflow pattern. This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and low-temperature small diffusion flames in lean overall equivalence ratios. In order to mature the hydrogen micromix combustion technology, high quality numerical simulations of the resulting short, thin and highly dynamic hydrogen flames, as well as predictions of combustion species, are essential. In fact, one of the biggest challenges for current CFD has been to accurately model this combustion phenomenon. The Flamelet Generated Manifold (FGM) model is a combustion model that has been used in the past decades for its predicting capabilities and its low computational cost due to its reliance on pre-tabulated combustion chemistry, instead of directly integrating detailed chemistry mechanisms. However, this trade for a lower computational cost may have an impact on the solution, especially when considering a fuel such as Hydrogen. Therefore, it is necessary to compare the FGM model to another combustion modelling approach which uses more detailed complex chemistry. The main focus of this paper then, is to compare the flame characteristics in terms of position, thickness, length, temperature and emissions obtained from LES simulations done with the FGM model, to the results obtained with more complex chemistry models, for hydrogen micromix flames. This will be done using STAR-CCM+ to determine the most suitable numerical approach required for the design of injection systems for ultra-low NOx.Item Open Access Development and application of a preliminary design methodology for modern low emissions aero combustors(SAGE, 2020-04-23) Liu, Yize; Sun, Xiaoxiao; Sethi, Vishal; Li, Yi-Guang; Nalianda, Devaiah; Abbott, David; Gauthier, Pierre Q.; Xiao, Bairong; Wang, LuIn this article, a preliminary design framework containing a detailed design methodology is developed for modern low emissions aero combustors. The inter-related design elements involving flow distribution, combustor sizing, heat transfer and cooling, emission and performance are coupled in the design process. The physics-based and numerical methods are provided in detail, in addition to empirical or semi-empirical methods. Feasibility assessment on the developed work is presented via case studies. The proposed combustor sizing methodology produces feasible combustor dimensions against the public-domain low emissions combustors. The results produced by the physics-based method show a reasonable agreement with experimental data to represent NOx emissions at key engine power conditions. The developed emission prediction method shows the potential to assess current and future technologies. A two-dimensional global prediction on liner wall temperature distribution for different cooling systems is reasonably captured by the developed finite difference method. It can be of use in the rapid identification of design solutions and initiating the optimisation of the design variables. The altitude relight efficiency predicted shows that the method could be used to provide an indicative assessment of combustor altitude relight capability at the preliminary design phase. The methodology is applied and shows that it enables the automatic design process for the development of a conceptual lean staged low emissions combustor. The design evaluation is then performed. A sensitivity analysis is carried out to assess the design uncertainties. The optimisation of the air distribution and cooling geometrical parameters addresses the trade-off between the NOx emissions and liner wall cooling, which demonstrates that the developed work has potential to identify and solve the design challenges at the early stages of the design process.Item Open Access Enabling cryogenic hydrogen-based CO2-free air transport: meeting the demands of zero carbon aviation(IEEE, 2022-06-02) Sethi, Vishal; Sun, Xiaoxiao; Nalianda, Devaiah; Rolt, Andrew Martin; Holborn, Paul; Wijesinghe, Charith; Xisto, Carlos; Jonsson, Isak; Grönstedt, Tomas; Ingram, James; Lundbladh, Anders; Isikveren, Askin; Williamson, Ian; Harrison, Tom; Yenokyan, AnnaFlightpath 2050 from the European Union (EU) sets ambitious targets for reducing the emissions from civil aviation that contribute to climate change. Relative to aircraft in service in year 2000, new aircraft in 2050 are to reduce CO2 emissions by 75% and nitrogen oxide (NOx) emissions by 90% per passenger kilometer flown. While significant improvements in asset management and aircraft and propulsion-system efficiency and are foreseen, it is recognized that the Flightpath 2050 targets will not be met with conventional jet fuel. Furthermore, demands are growing for civil aviation to target zero carbon emissions in line with other transportation sectors rather than relying on offsetting to achieve “net zero.” A more thorough and rapid greening of the industry is seen to be needed to avoid the potential economic and social damage that would follow from constraining air travel. This requires a paradigm shift in propulsion technologies. Two technologies with potential for radical decarbonization are hydrogen and electrification. Hydrogen in some form seems an inevitable solution for a fully sustainable aviation future. It may be used directly as a fuel or combined with carbon from direct air capture of CO2 or other renewable carbon sources, to synthesize drop-in replacement jet fuels for existing aircraft and engines. As a fuel, pure hydrogen can be provided as a compressed gas, but the weight of the storage bottles limits the practical aircraft ranges to just a few times that is achievable with battery power. For longer ranges, the fuel needs to be stored at lower pressures in much lighter tanks in the form of cryogenic liquid hydrogen (LH2).Item Open Access Injector design space exploration for an ultra-low NOx hydrogen micromix combustion system(ASME, 2019-11-05) Agarwal, Parash; Sun, Xiaoxiao; Gauthier, Pierre Q.; Sethi, VishalThe depletion of fossil fuel resources, as well as the increasing environmental concerns have become the driving forces towards the research and development necessary for the introduction of alternative fuel such as hydrogen into civil aviation. Hydrogen is a suitable energy source primarily because it is free of carbon and other forms of impurities and is also the most abundant element in the universe. The advantages of using Liquid Hydrogen (LH2) for civil aviation extends beyond carbon-free mission level emissions; LH2 combustion can potentially reduce NOx emission by up to 90%, providing long-term sustainability and unrivalled environmental benefits. The paper presents a simplified parametric analysis to investigate the influence of various injector design parameters on a hydrogen micromix combustor reactive flow field. The main characteristics investigated are the flame structure (shape and position), the aerodynamic stabilization of the flame and the resulting NOx emissions. The design parameters include variations in the air-feed dimensions and the hydrogen injection diameter. A suitable numerical model was established by comparing various turbulence modelling approaches, reaction mechanisms and turbulence-chemistry interaction modelling schemes. The predictive capabilities, and limitations, of each of these modelling approaches, are assessed. The numerical challenges and limitations associated with modelling H2/air combustion at high pressure and temperature conditions are detailed. The influence of varying the injector design parameters on the mixing and hence the NOx characteristics is assessed.Item Open Access Numerical investigation into the impact of injector geometrical design parameters on hydrogen micromix combustion characteristics(American Society of Mechanical Engineers, 2021-01-11) Sun, Xiaoxiao; Agarwal, Parash; Carbonara, Francesco; Abbott, David; Gauthier, Pierre Q.; Sethi, BobbyHydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. As a part of the ENABLEH2 project, the current study focuses on the influence of design parameters on the micromix hydrogen combustion injectors. This study provides deeper insights into the design space of a hydrogen micromix injection system via numerical simulations. The key geometrical design parameters of the micromix combustion system are the sizing of the air gates and the hydrogen injector orifices together with the offset distance between air gate and hydrogen injection, the mixing distance and the injector to injector spacing. This paper first presents results of the numerical simulation of four designs, down selected from a series of combinations of the key design parameters, including cases with low and high momentum flux ratio, weak and strong flame-flame interaction. It was discovered that the hydrogen/air mixing characteristics, and flame to flame interactions, are the main factors influencing the combustor gas temperature distributions, flame lengths and the corresponding NOx production. The current study then focused on the effect of air gate geometry on the mixing characteristics, flame shape and temperature distribution. The momentum flux ratio was kept constant throughout this investigation by keeping the air gate area constant. Variations of the original baseline air gate design were studied, followed by a study of various novel air gate geometries, including circular, semi-circular and elliptical shapes. It is concluded that NOx production is influenced by a number of factors including jet penetration flame interactions and air gate shape and that there is a “Sweet Spot” that results in the lowest practicable NOx production. Flatter and wider air gate shapes tend to yield the lowest temperature and consequently the lowest NOx. Reduced interaction between flames also tends to reduce NOx and by manipulating hydrogen penetration, there is the potential to further reduce the NOx production.Item Open Access Numerical investigation into the impact of operating boundary conditions on NOx formation in hydrogen micromix combustion system(American Society of Mechanical Engineers, 2023-09-28) Singh, Gaurav; Zghal, Malika; Sun, Xiaoxiao; Gauthier, Pierre; Sethi, VishalHydrogen micromix combustion is a promising technology for achieving zero mission-level carbon emissions with ultra-low NOx potential. A reduced-order NOx emissions prediction model is essential for preliminary hydrogen engine cycle design space exploration and optimization studies. Hence, this paper investigates the influence of key operating conditions, including equivalence ratio (ϕ), combustor inlet temperature (T3) and pressure (P3) on NOx emissions in a hydrogen micromix combustion. The assessments were performed using steady Reynolds-Averaged Navier-Stokes (RANS) simulations with thermal NOx model at various power conditions representative of the aircraft mission. The RANS model constants were calibrated against Large Eddy Simulations (LES) conducted previously by the group. The comprehensive numerical database was developed from these assessments to derive a NOx emissions correlation as a function of the operating conditions defined above. The study demonstrates that the LES-calibrated RANS models can predict NOx emissions trends, which agrees with the known physics of NOx formation. When experimental data is not yet available, the resulting correlation can be used at the preliminary stage of the design process to identify low NOx engine cycles that merit (more resource-intensive) higher fidelity numerical simulations or experiments. The methodology is flexible and extensible and may be applied to future low-emissions hydrogen combustion technologies.Item Open Access Numerical investigation of potential cause of instabilities in a hydrogen micromix injector array(American Society of Mechanical Engineers, 2021-09-16) Sun, Xiaoxiao; Abbott, David; Singh, Abhay Vir; Gauthier, Pierre; Sethi, BobbyHydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and small diffusion flames at lean overall equivalence ratios. There is limited published information on the instabilities of such hydrogen micromix combustors. Diffusion flames are less prone to flashback and autoignition problems than premixed flames as well as combustion dynamics issues. However, with the high laminar flame speed of hydrogen, lean fuel air ratio (FAR) and very compact flames, the risk of combustion dynamics for micromix flames should not be neglected. In addition, the multi-segment array arrangement of the injectors could result in both potential causes and possible solutions to the instabilities within the combustor. This paper employs numerical simulations to investigate potential sources of instabilities in micromix flames by modelling an extended array of injectors, represented by either single or multiple injectors with appropriate boundary conditions at elevated pressure and temperature. Both RANS and LES simulations were performed and used to derive the Flame Transfer Function (FTF) of the micromix flames to inform lower order thermoacoustic modelling of micromix combustion. LES simulations indicate that the gain of the FTF is lower than predicted from the RANS simulations indicating a lower risk of high frequency thermoacoustic issues than suggested by RANS. When LES simulations are conducted for certain representative configurations it is observed that there are persistent high-frequency instabilities due to the interaction of the flames. This phenomenon is not observed when only a single injector is modelled. LES simulations for two injectors are conducted with various geometries and radial boundary conditions to identify the cause of the instabilities. It is concluded that the observed high-frequency instabilities are related to aerodynamic jet instabilities enhanced by both aerodynamic and acoustic feedback and key geometric features affecting the occurrence of the instabilities are identified. Only transient simulations such as LES are able to capture such effects and RANS simulations typically used in early stage design will not identify this issue.Item Open Access Numerical investigation of the breakup mode and trajectory of liquid jet in a gaseous crossflow at elevated conditions(Cambridge University Press, 2021-09-13) Zhu, Yu; Sun, Xiaoxiao; Sethi, Vishal; Gauthier, Pierre; Guo, S.; Bai, R.; Yan, D.The commercial Computational Fluid Dynamics (CFD) software STAR-CCM+ was used to simulate the flow and breakup characteristics of a Liquid Jet Injected into the gaseous Crossflow (LJIC) under real engine operating conditions. The reasonable calculation domain geometry and flow boundary conditions were obtained based on a civil aviation engine performance model similar to the Leap-1B engine which was developed using the GasTurb software and the preliminary design results of its low-emission combustor. The Volume of Fluid (VOF) model was applied to simulate the breakup feature of the near field of LJIC. The numerical method was validated and calibrated through comparison with the public test data at atmospheric conditions. The results showed that the numerical method can capture most of the jet breakup structure and predict the jet trajectory with an error not exceeding ±5%. The verified numerical method was applied to simulate the breakup of LJIC at the real engine operating condition. The breakup mode of LJIC was shown to be surface shear breakup at elevated condition. The trajectory of the liquid jet showed good agreement with Ragucci’s empirical correlation.Item Open Access On the development of an experimental rig for hydrogen micromix combustion testing(The Combustion Institute, 2021-04-15) Giannouloudis, Alexandros; Sun, Xiaoxiao; Corsar, Michael; Booden, Scott J.; Singh, Gaurav; Abbott, David; Nalianda, Devaiah; Sethi, BobbyThis work describes the development of a combustion rig, aimed at testing hydrogen-fuelled micromix burners for aero gas-turbines at pressures up to 15barg, inlet-air temperatures up to 600K and equivalence ratios (Φ) from leanblow- out to 0.5. It discusses the test facility used, and the design procedure of the experimental apparatus: the requirements of it, the design choices and implementation of instrumentation. Emphasis is placed on the design and manufacture of the burner. Comparison between Additive Manufacturing (AM) and micro-machining techniques for the sub-millimetre injection points shows that further research is needed in this area, to achieve adequate geometric accuracy of the injection holes economically. This rig forms a unique facility for hydrogen micromix testing, offering simultaneous measurements of NOx emissions, Flame-Transfer–Function (FTF) and flame imaging.Item Open Access Preliminary aerodynamic design methodology for aero engine lean direct injection combustors(Cambridge University Press, 2017-06-21) Sun, Xiaoxiao; Liu, Yize; Sethi, Vishal; Li, JieThe Lean Direct Injection (LDI) combustor is one of the low-emissions combustors with great potential in aero-engine applications, especially those with high overall pressure ratio. A preliminary design tool providing basic combustor sizing information and qualitative assessment of performance and emission characteristics of the LDI combustor within a short period of time will be of great value to designers. In this research, the methodology of preliminary aerodynamic design for a second-generation LDI (LDI-2) combustor was explored. A computer code was developed based on this method covering the design of air distribution, combustor sizing, diffuser, dilution holes and swirlers. The NASA correlations for NOx emissions are also embedded in the program in order to estimate the NOx production of the designed LDI combustor. A case study was carried out through the design of an LDI-2 combustor named as CULDI2015 and the comparison with an existing rich-burn, quick-quench, lean-burn combustor operating at identical conditions. It is discovered that the LDI combustor could potentially achieve a reduction in liner length and NOx emissions by 18% and 67%, respectively. A sensitivity study on parameters such as equivalence ratio, dome and passage velocity and fuel staging is performed to investigate the effect of design uncertainties on both preliminary design results and NOx production. A summary on the variation of design parameters and their impact is presented. The developed tool is proved to be valuable to preliminarily evaluate the LDI combustor performance and NOx emission at the early design stage.Item Open Access Preliminary CFD Study on the effect of fuel injector coking on fuel spray characteristics(American Society of Mechanical Engineers (ASME), 2018-02-02) Agarwal, Parash; Sethi, Vishal; Gauthier, Pierre Q.; Sun, Xiaoxiao; Liu, YizeFuel injector coking involves deposit formation on the external or the internal surfaces of an injector or nozzle. This deposition of carbonaceous particles can result in uneven fuel-spray characteristics or localised burning (hot spots), which may eventually lead to mechanical failure or simply have a detrimental effect on the combustion system. This study focuses on the use of numerical methods to investigate the effect of coke formation on both the atomiser internal flow passages and its spray characteristics. Three different cases are examined; one investigating the clean injector; the second investigating the effect of internal coking; and the third investigating the effect of nozzle tip coking. A pressure swirl atomiser was considered for the purpose of the study. Validation of the numerical results for the clean injector condition is carried out against published experimental data. Two arbitrary geometries of coke deposits were created. The Volume of Fluid (VOF) multiphase model has been used in conjugation with a Geometrical Reconstruction Scheme (GRS) to simulate the interface representing the two phases. Spray cone angle and the liquid film thickness for the clean injector condition predicted by numerical simulation agreed well with the experimental data. Instabilities in the air core and the spray angle were also observed because of the presence of coke layers. Fouling present on the injector tip resulted in an earlier breakup of the film which can thereby affect the flame lift-off length. These stated observations can have significant implications both on the performance as well as the life of the combustion systems, thereby establishing the relevance of this study.Item Open Access Review of modern low emissions combustion technologies for aero gas turbine engines(Elsevier, 2017-09-12) Liu, Yize; Sun, Xiaoxiao; Sethi, Vishal; Nalianda, Devaiah; Li, Yi-Guang; Wang, LuPollutant emissions from aircraft in the vicinity of airports and at altitude are of great public concern due to their impact on environment and human health. The legislations aimed at limiting aircraft emissions have become more stringent over the past few decades. This has resulted in an urgent need to develop low emissions combustors in order to meet legislative requirements and reduce the impact of civil aviation on the environment. This article provides a comprehensive review of low emissions combustion technologies for modern aero gas turbines. The review considers current high Technologies Readiness Level (TRL) technologies including Rich-Burn Quick-quench Lean-burn (RQL), Double Annular Combustor (DAC), Twin Annular Premixing Swirler combustors (TAPS), Lean Direct Injection (LDI). It further reviews some of the advanced technologies at lower TRL. These include NASA multi-point LDI, Lean Premixed Prevaporised (LPP), Axially Staged Combustors (ASC) and Variable Geometry Combustors (VGC). The focus of the review is placed on working principles, a review of the key technologies (includes the key technology features, methods of realising the technology, associated technology advantages and design challenges, progress in development), technology application and emissions mitigation potential. The article concludes the technology review by providing a technology evaluation matrix based on a number of combustion performance criteria including altitude relight auto-ignition flashback, combustion stability, combustion efficiency, pressure loss, size and weight, liner life and exit temperature distribution.Item Open Access Thermoacoustic behaviour of a hydrogen micromix aviation gas turbine combustor under typical flight conditions(American Society of Mechanical Engineers, 2021-09-16) Abbott, David; Giannotta, Alessandro; Sun, Xiaoxiao; Gauthier, Pierre; Sethi, VishalHydrogen micromix is a candidate combustion technology for hydrogen aviation gas turbines. The introduction and development of new combustion technologies always carries the risk of suffering from damaging high amplitude thermoacoustic pressure oscillations. This was a particular problem with the introduction of lean premixed combustion systems to land based power generation gas turbines. There is limited published information on the thermoacoustic behaviour of such hydrogen micromix combustors. Diffusion flames are less prone to flashback and autoignition problems than premixed flames and conventional diffusion flames are less prone to combustion dynamics issues. However, with the high laminar flame speed of hydrogen, lean fuel air ratio (FAR) and very compact flames, the risk of combustion dynamics for micromix flames should not be neglected and a comparison of the likely thermoacoustic behaviour of micromix combustors and kerosene fueled aviation combustors would inform the early stage design of engine realistic micromix combustors. This study develops a micromix combustor concept suitable for a modern three spool, high bypass ratio engine and derives the acoustic Flame Transfer Function (FTF) at typical engine operating conditions for top of climb, take-off, cruise, and end of runway. The FTF is derived using CFD and FTF models based on a characteristic flame delay. The relative thermoacoustic behaviour for the four conditions is assessed using a low order acoustic network code. The comparisons suggest that the risk of thermoacoustic instabilities associated with longitudinal waves at low frequencies (below 1kHz) is small, but that higher frequency longitudinal modes could be excited. The sensitivity of the combustor thermoacoustic behaviour to key combustor dimensions and characteristic time delay is also investigated and suggests that higher frequency longitudinal modes can be significantly influenced by combustion system design. The characteristic time delay and thus FTF for a Lean Premixed Prevapourised (LPP) kerosene combustor is derived from information in the literature and the thermoacoustic behaviour of the micromix combustor relative to that of this kerosene combustor is determined using the same low order modelling approach. The comparison suggests that the micromix combustor is much less likely to produce thermoacoustic instabilities at low frequencies (below 1kHz), than the LPP combustor even though the risk in the LPP combustor is small. It is encouraging that this simple approach used in a preliminary design suggests that the micromix combustor has lower risk at low frequency than a kerosene combustor and that the risk of higher frequency longitudinal modes can be reduced by appropriate combustion system design. However, more detailed design, more rigorous thermoacoustic analysis and experimental validation are needed to confirm this.Item Open Access Validation of a stochastic breakup model for turbulent jets in high-speed crossflow: assessment of turbulent interactions and sensitivity to boundary conditions(Begell House, 2023-04-25) Zghal, Malika; Sun, Xiaoxiao; Gauthier, Pierre Q.; Sethi, VishalImproving the mixing of fuel and air by injecting a turbulent liquid fuel jet into a high-speed cross-flowing gas can reduce the emissions of gas turbine applications. To facilitate and hasten the development of such low-emissions technologies, accurate predictions of the spray characteristics are needed. The objective of the present study is to validate the predictive capabilities of a stochastic breakup model for turbulent transverse jets over a wide range of representative pressures and atomization characteristics. The effect of turbulence modeling is also assessed to provide accurate and computationally less expensive Eulerian−Lagrangian transient approaches. To do so, the predictions made with the large eddy simulation (LES) approach for different subgrid-scale (SGS) models and with the synthetic eddy method (SEM) are compared to the ones made using the unsteady Reynolds-averaged Navier-Stokes (RANS) approach with and without a turbulent dispersion model. The sensitivity of the numerical methodology to the upstream velocity profile, pressure, and momentum flux ratio were also assessed. Properly accounting for the upstream gas velocity profile was found to be critical to ensure accurate predictions of the spray characteristics. The unsteady RANS (URANS) turbulent approach coupled with the turbulent dispersion model showed good agreement with experimental data, but the LES approach tends to overpredict the spray penetration and underpredict the Sauter mean diameter (SMD). This could be due to the lower turbulent interactions it predicts, which may lead to lower momentum transfer between the phases.