Browsing by Author "Liu, Yize"

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    Combustor development and performance analysis for recuperated microturbine application
    (AIAA, 2021-07-28) Liu, Yize; Nikolaidis, Theoklis; Gamil, Abdelaziz; Madani, Seyed Hossein; Sarkandi, Mohammad
    In recent years, increased attention is paid to the microturbine MGT as a promising technology for combined heat and power (CHP) applications. An MGT has advantages of high reliability, high efficiency, lower manufacturing and maintenance costs, reduced vibration and noise levels, and clean emissions. Recuperation can further increase efficiency by recycling the heat from the turbine exhaust and preheating the air for combustion via a heat exchanger. Such a system will be realized by designing a combustion chamber that can meet various design and operability requirements. This paper presents an overview of the combustor development and provides CFD analysis on combustor performance and emissions. A single tubular combustor is designed, and the direct injection mode is applied to mitigate the autoignition and flashback risks resulting from the high preheating temperature. Heat transfer and cooling analysis indicate that ceramic liner is capable of tolerating high temperature using effusion cooling. Studies of flow characteristics, temperature field, pressure loss, and pattern factor are provided in detail. The effects of design parameters and methods (i.e., fuel-air mixture strength, cooling hole angles, dilution hole design approaches) are also discussed. Finally, the use of biomass is investigated and shows that it has the potential to achieve a high combustion efficiency and low emissions for the recuperated microturbine application.
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    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, Lu
    In 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.
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    Initial experimental testing of a hybrid solar-dish Brayton cycle for combined heat and power (ST-CHP)
    (Elsevier, 2024-05-18) Swanepoel, Jonathan K.; le Roux, Willem G.; Roosendaal, Casey; Madani, Seyed H.; de Wet, Gideon; Nikolaidis, Theoklis; Roosendaal, Westley; Onorati, Chase; Sciacovelli, Adriano; Liu, Yize; Mokobodi, Tlou S.; McGee, Duncan S.; Craig, Ken J.
    The Solar Turbo Combined Heat and Power (ST-CHP) project developed a novel solar-gas hybrid prototype for combined heat and power generation in Pretoria, South Africa. A vacuum-membrane faceted parabolic dish with a large-pipe open-cavity receiver was coupled to a counterflow recuperator, a combustion chamber, a micro gas turbine with air bearings and a phase change thermal energy storage unit containing solar salts. This study aimed to validate the electrical output of the full-scale dish-Brayton prototype, addressing the literature gap on micro-scale dish-Brayton plants' in-field power generation. Solar hybridization of micro gas turbine technology can significantly reduce combustion fuel consumption. A performance analysis under relevant conditions revealed a late afternoon micro gas turbine output intermittently peaking at 0.4 kWe and subsequently stabilizing to a steady state of 0.145 kWe at 130 krpm. A SimuPact numerical model and an analytical model supplemented the telemetry data to reduce interference in the experimental setup and fully characterize the ST-CHP prototype performance, estimating a steady-state turbine isentropic efficiency of 57%, a compressor efficiency of 71% and a collector efficiency of 17% due to the late afternoon steady-state point. Analytical case studies revealed that fuel savings of between 12% and 33% at the combustion chamber were achievable from the solarized preheating. A subsequent test of the micro gas turbine without solar hybridization or a recuperator resulted in 1.05 kWe being generated. The study confirms the dish-Brayton prototype's viability for combined heat and power generation, producing an initial full-scale performance characterisation during in-field testing, and highlighting the impact of solar hybridization on turbine electrical output. Optical efficiency, insulation effectiveness, pressure losses, and turbine operating conditions were identified as critical areas requiring optimization to improve electrical output. The lessons learned, and the calibrated numerical model may be used to optimize the performance of the dish-Brayton plant in future work. The successful in-field full-scale power generation of the ST-CHP prototype adds to the available literature on dish-Brayton technology and brings the technology closer to a commercial product.
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    Multi-fidelity combustor design and experimental test for a micro gas turbine system
    (MDPI, 2022-03-23) Liu, Yize; Nikolaidis, Theoklis; Hossein Madani, Seyed; Sarkandi, Mohammad; Gamil, Abdelaziz; Firdaus Sainal, Muhamad; Vahid Hosseini, Seyed
    A multi-fidelity micro combustor design approach is developed for a small-scale combined heat and power CHP system. The approach is characterised by the coupling of the developed preliminary design model using the combined method of 3D high-fidelity modelling and experimental testing. The integrated multi-physics schemes and their underlying interactions are initially provided. During the preliminary design phase, the rapid design exploration is achieved by the coupled reduced-order models, where the details of the combustion chamber layout, flow distributions, and burner geometry are defined as well as basic combustor performance. The high-fidelity modelling approach is then followed to provide insights into detailed flow and emission physics, which explores the effect of design parameters and optimises the design. The combustor is then fabricated and assembled in the MGT test bench. The experimental test is performed and indicates that the designed combustor is successfully implemented in the MGT system. The multi-physics models are then verified and validated against the test data. The details of refinement on lower-order models are given based on the insights acquired by high-fidelity methods. The shortage of conventional fossil fuels and the continued demand for energy supplies have led to the development of a micro-turbine system running renewable fuels. Numerical analysis is then carried out to assess the potential operation of biogas in terms of emission and performance. It produces less NOx emission but presents a flame stabilisation design challenge at lower methane content. The details of the strategy to address the flame stabilisation are also provided.
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    Performance and emission assessment of thermo-electric power plant for rotorcraft propulsion
    (American Society of Mechanical Engineers, 2021-01-11) Roumeliotis, Ioannis; Arena, Francesco; Liu, Yize; Vouros, Stavros; Pachidis, Vassilios; Broca, Olivier; Toure, Djiby; Unlu, Deniz
    This paper assesses a gas turbine based parallel rotorcraft hybrid electric propulsion system in terms of overall performance and emissions. Three different electric power train technology levels and three different power management strategies are considered for identifying the potential benefits of hybridization in relation to technology advancements and quantifying the effect of PMS. For this analysis, a Passenger Air Transport of a twin-engine medium helicopter is used. The propulsion systems mission simulation and emissions calculation are performed in Simcenter Amesim. The assessment framework integrates a thermal power-plant model, an electric power plant model for the hybrid electric cases, a helicopter simulation model and suitable pollutant emissions calculation correlations. For establishing NOx emission correlations that can be used for turboshaft engine calculations, a systematic evaluation of different correlations available in the literature is performed. The correlations are compared for different operating points against a calibrated stirred reactor model. The suitable correlations are utilized in the framework. The propulsion system is sized according to the technology levels and power management strategy considered, updating the helicopter Take-Off Weight for each case. The results indicate that there is potential for efficiency betterment and CO2 emissions reduction. The benefits strongly depend on the power management strategy and energy and power density of the electric power train. For current technology level and for the cases examined herein no benefits in terms of overall performance and emissions accrue. If future technology level is considered, hybridization may offer benefits in terms of performance to the expense of NOx emissions for the case that the power train is used for boosting and the gas turbine is scaled down. Power splitting may offer block fuel, turbine life and NOx benefits to the expense of overall energy performance.
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    Preliminary aerodynamic design methodology for aero engine lean direct injection combustors
    (Cambridge University Press, 2017-06-21) Sun, Xiaoxiao; Liu, Yize; Sethi, Vishal; Li, Jie
    The 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.
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    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, Yize
    Fuel 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.
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    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, Lu
    Pollutant 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.