Gas Turbine Research Articles

Lifing Assessment of Gas Turbine Blade Root Affected by Out-of-Tolerances.

Current and future heavy-duty gas turbines (GTs) are being developed as an alternative or support to renewable energy sources (RESs). Therefore, GTs are subjected to several instances of being switched on and off; thus, the material fatigue limit can be reached in a short time. In such a scenario, possible out-of-tolerances (OoTs) in critical components must be considered. In this paper, OoTs related to critical parameters in the attachment geometry of a rotor blade are considered to estimate their impact on component life through a 2D finite element (FE) analysis. First, a mesh refinement is performed to obtain mesh-independent results; second, OoT geometries are simulated to determine stresses and strains at the blade attachment and disc groove. The mesh refinement process is critical to ensure model accuracy for both nominal and OoT geometries. The results show that OoTs can lead to important reductions in the life of the intended component, both on the blade and disc sides. These results could be useful in updating the maintenance plan for components and could be used for future insights, with further work extending the study to 3D geometry, for example, and evaluating the effect of other geometries.

Environmental barrier coatings on alumina-reinforced CMCs: Experimental validation and numerical modeling of thermal stability

Recent advancements in ceramic matrix composites (CMCs), including SiC/SiC, C/SiC, C/C, Al2O3 reinforced Al2O3, face various challenges at high temperature applications, including grain growth, sintering, and creep deformation which are leading to strength loss. The new generation of Environmental Barrier Coatings (EBCs) must allow the protection of these CMCs when operating under harsh conditions, which can reach up to 1100 °C in some applications, such as gas turbines and certain reforming processes. In this work, 8 wt% yttria stabilized zirconia (8YSZ) applied by Atmospheric Plasma Spraying (APS) on top of a porous alumina oxide matrix with reinforced alumina fibers Al2O3/Al2O3-CMC (OCMC), considering different interfaces, has been studied. Surface morphology and pre-treatment of CMCs is the most challenging part for thermal spray applications. Hence, two different surface structure were used in this work. The results show that the roughness of OCMC can be reduced from Rz = 41.8±6.8 μm to 20.3±1.1 μm with the new porous bond coat and plasma sprayed coating, resulting in a homogeneous surface morphology.. In terms of thermal stability, a numerical model that combines Object Oriented FEM (OOF) and Cohesive Zone Model CZM tools, has been developed to evaluate the effect of the porosity of the real microstructure and the characteristics of the interfacial roughness profile, respectively, in CMC/EBC structures. In addition, other materials, such as La2Zr2O7 and Y2O3, have been numerically studied in order to evaluate their suitability as EBC.

Feedback control of thermoacoustic instabilities in sequential combustor with nanosecond repetitively pulsed discharges

Controlling thermoacoustic instabilities is a necessary task for the development and operation of gas turbines. With the increasing proportion of renewable energy sources, gas turbines must have flexibility in terms of both fuel and load. This implies that thermoacoustic instabilities must be controlled under different operating conditions. Active control strategies are indeed very suitable in this case, as they can adapt to the changes in operating conditions. Nanosecond repetitively pulsed discharges (NRPD) has shown to be promising active control actuators because they require no moving parts. In this study, the effectiveness of feedback and open-loop control law with NRPD actuation to suppress thermoacoustic instabilities in a lab-scale sequential combustor is evaluated. The effect of the controller parameters on the NO emissions of the combustor is also quantified. The results indicate that there is a trade-off between acoustic pulsation reduction and NO emission.

A dual-standby power source configuration scheme for micro grid in Pelagic Island

Realizing clean energy supply is important for the sustainable development of pelagic island. The volatility and randomness features of renewable energy generation may reduce power supply reliability, thus backup units is necessary in micro-grid in pelagic island. This paper proposed a dual-standby configuration scheme based on Sequence Operation Theory to achieve reliable power standby. Firstly, characteristics of standby units, micro gas turbine and diesel generator, are analyzed. Next, the probability distribution function models of wind, photovoltaic and load demand in pelagic island are established, and the reliability index of power shortage probability is calculated by Sequence Operation Theory. Then, the two-stage dual-standby control scheme to make full use of the complementary standby units is introduced and object function to minimize equivalent annual cost on the premise of satisfying probabilistic reliability index is modeled. Hybrid integer particle swarm algorithm is used to solve the problem. Finally, the proposed model for dual-standby configuration is applied to a pelagic island. The simulation results show that the proposed method can meet the load demand in both daily and extreme weather and achieve superior economy.

Fuel blend combustion for decarbonization

The utilization of fossil fuels is currently transforming to low-carbon or zero-carbon fuels, which is one of the solutions to global warming. Hydrogen and ammonia are regarded as promising zero-carbon fuels in power supply and transportation scenarios but the availability of hydrogen and their distinctly different chemical activity constrain their large-scale direct utilizations. Fuel blends with physical and chemical complementary are considered as the effective approaches in the utilization of hydrogen and ammonia because no significant modification to the existing end-user infrastructures is needed. This paper reports recent progress in the fundamental combustion behaviors of fuel blends, focusing on hydrogen-hydrocarbon blends and ammonia-hydrocarbon blends. Firstly, laminar flame behaviors, auto- and forced-ignition characteristics, and pollutant emissions of binary fuels containing hydrogen are reviewed, all of which are supplemented with a discussion on the governing hydrogen-enriched combustion chemistry. Subsequently, the hydrogen-enriched flame responses to the flow conditions are discussed, including the turbulent burning velocity and statistical structures, the flashback swirl flames, thermoacoustic instabilities, and the jet ignition characteristics; Furthermore, with the increasing concern over ammonia as a zero carbon fuel and its extremely weak reactivity, recent progress on combustion of fuel blends containing ammonia are also reviewed. The fundamental combustion chemistry studies including laminar burning velocity, the ignition delay times data collection, as well as the attempts for chemical kinetic modeling development for fuel blend with ammonia are presented. The literature reported ammonia containing blends of turbulent flame characteristics are presented. Finally, from an engineering point of view, examples using hydrogen blends in practical internal combustion engines and in gas turbines are introduced, including the topic of engine efficiency performance and pollutant emissions and different combustors for gas turbines. It is suggested that fuel blends with hydrogen or ammonia that potentially monitors the overall reactivity will be one realistic solution to de-carbonization, on the basis of current transportation and power generation systems.

Combined cycle gas turbine (CCGT) plants utilizing methane-hydrogen blends represent a significant element in Australia’s journey toward achieving net-zero emissions

To deliver 570 TWh of dispatchable electricity to the grid in Australia, it is necessary to build up wind and solar photovoltaic power plants generating capacity of 325 GW, and a long-term hydrogen energy storage system comprising 50–150 GW of electrolyzers, 50 TWh of hydrogen storage, and 165 GW of hydrogen power generation. While the addition of other renewable energy producers and energy storage technologies effective on shorter scales are certainly welcome and positively impact the above demand, the inclusion of inter-annual variability and safety negatively impacts these numbers. Fuel cells are currently less advanced compared to electrolyzers and hydrogen storage in salt caverns. Expanding hydrogen power generation will require exploring additional opportunities. Here we advocate for methane-hydrogen Combined Cycle Gas Turbine (CCGT) plants. Their adaptability to effortlessly integrate methane and green hydrogen mixtures positions them as a key player in the evolution toward net zero. This transition will be complete once a fully established wind and solar photovoltaic generation, coupled with an efficient hydrogen energy storage system, is in place. Notably, these CCGT plants consistently yield the lowest Life Cycle Analysis (LCA) carbon dioxide (CO2) emissions during the grid’s progression toward net zero.

Investigation on the effects of swirl-strength on flashback phenomenon of premixed CH[formula omitted]/H[formula omitted]/air flame in a bluff-body swirl burner

Blending a low ratio of hydrogen into traditional hydrocarbon fuels can reduce the modification in structure of existing combustors. However, even a low hydrogen ratio can increase the propensity of flashback due to the extremely high reactivity of hydrogen. Swirl number is a key parameter of swirl combustors which determines the flow structure. To design reliable gas turbine combustors for hydrogen-blended fuels, the study in the effect of swirl strength on flashback characteristic and the underlying mechanism is necessary. In this study, the flashback characteristics of premixed 30% H2/70% CH4/air flame in a bluff-body swirl burner is investigated via both experiment and large-eddy simulations with the flamelet-generated-manifold method (FGM-LES). The flashback mode and flame-flow interaction are analyzed based on the LES results. It is found that the increase in swirl strength will increase the propensity of flashback and promote the flashback speed of premixed 30% H2/70% CH4/air flame in the bluff-body swirl burner. The turns from Mode II (small-scale flame bulges leading flashback) to Mode I (large-scale swirling flame tongue leading flashback) during flashback of hydrogen-blended flames due to the production of stronger reversed flow by swirling flow. It is also found that stronger swirl strength will result in a smoother flame front and narrower strain rate distribution range which suppresses the local hydrogen enrichment due to preferential diffusion of hydrogen, thus suppressing the flame propagating speed. However, this effect is not dominant in flashback process compared to the promotion of reversed flow by increased swirl strength.

Effect of entropy waves generated by different flame models on the thermoacoustic instability

Thermoacoustic instability can be an important problem for aero-engine and gas turbine combustion chambers, especially for lean premixed combustors designed for low NOx emissions. This instability is caused by the interaction of acoustic waves with unstable heat release. Entropy waves generated in the combustion chamber also produce acoustic waves during acceleration, known as indirect combustion noise or entropy noise, which are reflected upstream to affect the thermoacoustic instability. In this paper, the effect of entropy waves generated by different flame models on the thermoacoustic instability is investigated, and the main controlling factors and coupling mechanisms of entropy thermoacoustic modes are studied, in which both flames and entropy waves break the original acoustic field and introduce new modes. It is found that entropy waves change the modal frequency of ITA, the choked outlet and the flame plane may form similar boundary conditions with the same time delay for ITA modes. In addition, the filter flame decreases the frequency of entropy thermoacoustic modes and ITA modes.

Investigating the performance of a gas turbine system combined with steam methane reforming as a thermochemical recuperator in a power, cooling, freshwater, and hydrogen production multigeneration system

Depletion of fossil fuel resources at a high speed and increasing demand for energy supply for various purposes in today's life integrated with industry has led to collective contemplation for the optimal and maximum utilization of fossil fuels through the implementation of multigeneration systems. In the presented study, a multigeneration system for cooling, power, freshwater, and Hydrogen production is proposed and investigated from exergy, energy, and economic viewpoints through a specific scenario. A case study is performed, revealing that the system can deliver a net output power of 16,251.8 kW, a cooling load of 15,905.0 kW, produce freshwater at a rate of 3.891 kg/s, and generate hydrogen at 0.284 kg/h. The energy and exergy efficiencies of the system are 60.48 % and 32.55 %, respectively. An economic analysis shows a payback period of 0.474 years. A parametric evaluation is performed to perceive the system operation in various conditions. Subsequently, a multi-objective optimization using the MOPSO-LINMAP method is conducted to identify the optimal operating conditions for the system. The optimization results are compared with the case study findings, demonstrating further improvements in performance metrics. The optimized system achieves a slightly higher energy efficiency of 61.62 % and a lower payback period of 0.40 years, underscoring the benefits of the optimization process. This study highlights the potential of the proposed system to efficiently and economically meet the demands for power, hydrogen, cooling, and freshwater in various applications.

High-frequency transverse acoustic interactions between two lean-premixed hydrogen combustors connected with cross-fire and cross-talk sections

Large-scale inter-combustor thermoacoustic interactions occur frequently in modern can-annular gas turbine combustion systems due to the presence of an annular cross-talk section upstream of the first stage turbine stator vanes. Although the whole system's modal dynamics depend on the relative dominance of low-frequency planar or high-frequency transverse acoustic waves, the majority of prior studies have chiefly focused on longitudinal mode instabilities. Motivated by the paucity of detailed information, here we examine high-frequency transverse acoustic interactions between two adjacent lean-premixed hydrogen combustors connected via two different pathways, known as cross-fire (XF) and cross-talk (XT) sections. We observe that the dual-combustor system undergoes high-frequency spinning mode in the clockwise direction, manifested as well-defined limit cycles with peak-to-peak amplitude of around 10 kPa. The transverse pressure oscillations, in contrast to the well-established low-frequency mutual synchronization dynamics, are not fully synchronized even in the presence of cross-talk communication. This situation leads to the formation of two closely-spaced 1T modes at 4.76 and 4.86 kHz in the respective hydrogen combustors, accompanied by the beating of the pressure fluctuations solely in the XF tube section. Remarkably, the pressure waves induced near the XF tube section tend to lag behind the pressure waves spinning in the injector face, demonstrating the existence of the angular shift characteristically connected to the high-frequency transverse combustion dynamics.

A Comprehensive Literature Review on The Resolution of Turbine Engine Performances' Inverse Problems

A Comprehensive Literature Review on The Resolution of Turbine Engine Performances' Inverse Problems

Effect of Different Nozzle Arrangements on Combustion Flow Characteristics in a Swirl Coupling Multiple Direct Injection Combustor

ABSTRACT The influence of multiple direct injection nozzle arrangements with hexagonal, rhombus, and circular shapes on the combustion flow in gas turbines was numerically studied, and the combustion flow characteristics of swirl combustion combined with multiple direct injection combustion were analyzed, such as velocity and temperature distribution, vortex structure, NOX (nitrogen oxides) emission, flame stretch rate, etc. The result shows that for these different nozzle arrangements, the difference in velocity and temperature distribution is not obvious, but the difference in vortex structure is large. The hexagonal arrangement can form several counter-rotating vortex pairs (CVP) near the side wall, the rhombus arrangement can form several deflection vortex structures outside the center swirl, and the circular arrangement forms the least vortex structure. Furthermore, the circular arrangement is most effective in reducing the non-uniformity of the outlet temperature, OTDF is 0.00548, and it has a higher flame stretch rate, which means that it has a higher combustion intensity. However, the hexagon arrangement has the higher NOX emission, reaching 3.16 ppm.

Sustainable Energy Application of Pyrolytic Oils from Plastic Waste in Gas Turbine Engines: Performance, Environmental, and Economic Analysis

The rapid accumulation of polymer waste presents a significant environmental challenge, necessitating innovative waste management and resource recovery strategies. This study investigates the potential of chemical recycling via pyrolysis of plastic waste, specifically polystyrene (PS) and polypropylene (PP), to produce high-quality pyrolytic oils (WPPOs) for use as alternative fuels. The physicochemical properties of these oils were analyzed, and their performance in a gas turbine engine was evaluated. The results show that WPPOs increase NOx emissions by 61% for PSO and 26% for PPO, while CO emissions rise by 25% for PSO. Exhaust gas temperatures increase by 12.2% for PSO and 8.7% for PPO. Thrust-specific fuel consumption (TSFC) decreases by 13.8% for PPO, with negligible changes for PSO. The environmental-economic analysis indicates that using WPPO results in a 68.2% increase in environmental impact for PS100 and 64% for PP100, with energy emission indexes rising by 101% for PS100 and 57.8% for PP100, compared to JET A. Although WPPO reduces fuel costs by 15%, it significantly elevates emissions of CO2, CO, and NOx. This research advances the understanding of integrating waste plastic pyrolysis into energy systems, promoting a circular economy while balancing environmental challenges.

Upgraded one-dimensional code for the design of a micro gas turbine mixed flow compressor stage with various crossover diffuser configurations

Abstract Micro Gas Turbine (MGT) designers often have the need for a design tool, capable of rapidly providing feasible design options. The upgrade of such an existing MATLAB® based mixed flow compressor design application (1D App) is discussed. In MGT engines, diffuser design largely influences the compressor stage performance. Crossover diffusers provide superior efficiency and pressure ratio performance compared to legacy type diffusers, albeit at the expense of operating range. The reduced operating range attributed to single vane crossover diffusers can be alleviated by splitter vane, tandem vane, and combined configurations. Therefore, the 1D App is updated to allow the user the ability to design these additional crossover diffuser configurations. Performance results are verified using Numeca/FINE™ Turbo CFD software. It is shown that the upgraded 1D App provides predicted performance results within 1 % of CFD results for both total-to-total efficiency and pressure ratio.

Thermodynamic analysis of supercritical CO2 power generation system for waste heat recovery with impurities in CO2

Waste heat recovery from gas turbines is an effective method for meeting the demand for a more efficient and cleaner energy system with decreased CO2 emissions and lower environmental pollution. The supercritical CO2 Brayton cycle is a promising power conversion system for waste heat recovery. The advantage of the supercritical CO2 Brayton cycle can be attained based on its physical characteristics. However, when another fluid is mixed as an impurity in a system using pure CO2, physical characteristics of working fluid was changed and operation at the design point can be challenging. Therefore, it is important to verify the purity of CO2 and understand the effect of impurities in CO2 in advance. This study examined the effects of impurities in the working fluid of a supercritical CO2 power generation system for actual demonstration facilities. The effect of impurity, a CO2-based mixture, in a supercritical CO2 power generation system on waste heat recovery from an LM500 gas turbine was investigated. A purity test of industrial grade CO2, which was noted as 99.9 % pure by the supplier, was conducted to verify the composition of the working fluid. The results of the purity test showed that the supplied CO2 consisted of 99.076 % CO2 along with nitrogen, argon, oxygen, water, and methane. Based on the results of the purity test, sensitivity analyses of the CO2-based binary mixtures and industrial mixtures were performed. A design point analysis was conducted for the CO2-based industrial mixture in comparison with pure CO2, which has cycle efficiency of 16.15 %, gross power of 510.03 kW, mass flow rate of 12.55 kg/s, and waste heat recovery of 2119.06 kW. In the case of fixed waste heat with mass flow rate of 14.417 kg/s, the cycle efficiency decreased by 0.39 % and gross power increased by 66.14 kW. In the case of fixed mass flow rate with 1844.598 kW waste heat, the cycle efficiency decreased by 0.32 % and gross power decreased by 9.84 kW. In addition, the influence of the performance of the major components on the system performance was investigated.

Optimization and exergoeconomic analysis of a biomass-driven cogeneration system for power and cooling applications

Due to the increasing population and the expansion of industry in daily life, a significant depletion of fossil fuel resources is observed, accompanied by escalating environmental concerns. In response to these challenges, this study presents an optimized cogeneration system powered by renewable biomass, designed for simultaneous power and cooling generation. The system integrates a biomass gasification unit, a steam Rankine cycle, a helium-driven gas turbine cycle, and an ammonia-water-based two-stage absorption refrigeration cycle with a bleed line. Thermodynamic and exergoeconomic analyses reveal a net power output of 5356 kW, a cooling load of 360.9 kW, and an exergetic efficiency of 29.52 %. Financially, the system shows a net present value of 11.76 $M and a payback period of 6.51 years. A multi-objective optimization utilizing the gray wolf algorithm improves system performance through the employment of three diverse scenarios, which raises power output to 5864 kW, cooling load to 372 kW, and optimize net present to 14.28 $M with a reduced payback period of 5.96 years. The studied system is well-suited for industrial applications, rural electrification, and district energy systems, and offers a sustainable and economically viable energy solution.

Thermodynamic investigation of the efficiency of ammonia-powered marine solid oxide fuel cells with gas turbine

Improvement of marine power plants includes increasing their efficiency and drastically reducing emissions of pollutants, which involves transitioning to carbon-free fuels. This article discusses the evolution of a marine power system designed for decarbonization, utilizing ammonia and comprising solid oxide fuel cells with a gas turbine. To enhance efficiency, the system incorporates a steam supply into the fuel burning device of a gas turbine. By adding superheated steam, the system's performance improves significantly. Thermodynamic calculations identified optimal parameters for the gas turbine, which enhances efficiency by utilizing off-gases from the fuel cells. Key parameters include compressor and exhauster pressure ratios, which can be used to increase the specific power. A combined energy system with an overexpansion turbine achieves a total efficiency of 60.62 % at a fuel cell temperature of 1190 K during operation, with the SOFC efficiency being 43.76 %. These findings highlight potential improvements for marine power systems using ammonia and provide insights into the energy conversion processes within such hybrid systems.

Experiment and dynamic simulation of micro gas turbine combined with concentrated solar power system

The solar micro gas turbine (SMGT) system is a promising solution to address the instability and intermittency of renewable energy sources. Its dynamic characteristics under unstable input conditions and uncertain output load demands are crucial for peak shaving. This paper constructs an SMGT system based on experiments with micro gas turbine (MGT) and concentrated solar power (CSP), analyzing the impact of integrating CSP system on the MGT. Then the performance of the SMGT under varying ambient conditions and load demands is studied. Results show that in grid-connected mode, the turbine speed of MGT and SMGT is determined by ambient temperature and set power, with electrical efficiency decreasing as temperature and DNI increase. The solar receiver in the SMGT should maximize temperature increase while maintaining pressure loss below 55 kPa. Additionally, a higher heat capacity can reduce sensitivity to ambient changes but also extends stabilization time. Under real solar radiation, the SMGT system can keep constant power within 0.6% fluctuation, with a solar share of 36.5%. When combined with photovoltaic, the hybrid system’s maximum power fluctuation does not exceed 2.6%, with a solar share of 48.8%. This study provides guidance for optimizing SMGT systems and their application in peak shaving scenarios.

Development of a flexible phased array electromagnetic acoustic testing system with array pickups

The thermal barrier coatings (TBCs) used to protect blades of heavy-duty gas turbines is prone to debonding defects during fabrication and service. It is difficult to detect the debonding defects in the TBC system non-destructively and in situ due to the curved shape of blade and the narrow space between the blades setting in the gas turbine. In this paper, a flexible phased array electromagnetic acoustic (FPA-EMA) testing system with array pickups is developed, which is capable to drive a flexible phased array electromagnetic acoustic transducer (FPA-EMAT) to generate and receive ultrasonic wave directly in the metallic substrate of TBCs, and is potential to be applied to the inspection of debonding defects in the TBC system of gas turbine blades. A phased array excitation unit, a multi-channel signal receiving unit and a new signal post-processing algorithm are developed for the new EMA testing system to enhance the surface acoustic wave in the layered structure and to improve the low conversion efficiency of the conventional EMA testing system. In addition, a bias magnetic field coil fed with long pulse current of large amplitude is adopted to make the new EMAT thin and flexible in order to be applied in a narrow space. The interfering noise and geometric size problems brought by the multiple excitation and pickup channels are well addressed in the new system. The good performances of the developed FPA-EMA testing system were verified experimentally and show the system of good potential to be applied to NDT of practical curved structures.

Surface roughness effects in a transonic axial flow compressor operating at near-stall conditions

Surface roughness is a major contributor to performance degradation in gas turbine engines. The fan and the compressor, as the first components in the engine's air path, are especially vulnerable to the effects of surface roughness. Debris ingestion, accumulation of grime, dust, or insect remnants, typically at low atmospheric conditions, over several cycles of operation are some major causes of surface roughness over the blade surfaces. The flow in compressor rotors is inherently highly complex. From the perspective of the component designers, it is, thus, important to study the effect of surface roughness on the performance and flow physics, especially at near-stall conditions. In this study, we examine the effect of surface roughness on flow physics such as shock-boundary layer interactions, tip and hub flow separations, the formation and changes in the critical points, and tip leakage vortices among other phenomena. Steady and unsteady Reynolds Averaged Navier Stokes calculations are conducted at near-stall conditions for smooth and rough National Aeronautics and Space Administration rotor 67 blades. Surface streamlines, Q-criterion, and entropy contours aid in analyzing the flow physics qualitatively and quantitatively. It is observed that from the onset of stall, to fully stalled conditions, the blockage varies from 21.7% to 59.6% from 90% span to the tip in the smooth case, and from 40.5% to 75.2% in the rough case. This significant blockage, caused by vortex breakdown and chaotic flow structures, leads to the onset of full rotor stall.