Gas Turbine Combustor Research Articles

Characteristics of Mathematical Modeling of Acoustic Emission Method for Diagnosis of Fatigue Cracks in the Elements of Marine Power Plants

Abstract This article analyses the main characteristics of marine power plants, which include internal combustion engines (ICE) and gas turbine engines (GTE). At the same time, gas turbines are considered in comparison with aircraft engines. The study considers the possibility of using the acoustic emission (AE) method to evaluate the fatigue resistance of critical elements of ICE and GTE, based on the valve block in the ICE and turbine rotor blades. AE criteria for determining the growth of fatigue cracks are analysed, a method for evaluating individual durability and a method for calculating crack length are proposed.

Manipulating hydrogen oxy-combustion through carbon dioxide addition

Hydrogen (H2) is increasingly viewed as an attractive carbon-free fuel due to its potential compatibility with the existing transportation and conversion infrastructure. However, one of the major challenges facing large-scale deployment is the fundamentally different combustion properties it has in comparison to commonplace hydrocarbon fuels such as natural gas. For example, the laminar burning velocity (LBV) of a combustible mixture has a direct impact on how it can be used in internal combustion engine or gas turbines; the LBV of hydrogen is over 7 times greater than that of natural gas when combusted in air. Carbon dioxide (CO2) can be used as a working fluid, as opposed to nitrogen (in air), to reduce the flame speed of hydrogen combustion. A mixture of hydrogen, oxygen, and carbon dioxide as a working fluid can provide LBVs comparable to natural gas in air, which potentially enables existing conversion architectures. Furthermore, by replacing nitrogen (N2) with CO2 in the mixture, NOx emissions are avoided and opportunities for carbon sequestration or closed-cycle processes are possible. This study experimentally explores fundamental premixed oxy-combustion properties of H2-CO2 mixtures in a constant volume combustion chamber (CVCC) across a range of initial pressures (1, 1.5, and 2bar) and equivalence ratios (0.4, 0.6, 0.8, and 1). The spherically expanding flames are examined to determine the flame speed, LBV, and lower flammability limits (LFL) with respect to different CO2 concentrations (40%, 60%, 65%). Furthermore, at an initial pressure of 1bar and stoichiometric conditions, it was found that the flame speed of the 65% CO2 case was lower than that of CH4-air combustion.

Experimental Study on Flame Response Characteristics of a Non-Premixed Swirl Model Combustor

Non-premixed swirl combustion has been widely used in pieces of industrial combustion equipment such as industrial boilers, furnaces, and certain specific gas turbine combustors. In recent years, the combustion instability of non-premixed swirl flames has begun receiving attention, yet there is still a lack of related research in academia. Therefore, in this study, we conducted experimental research on a swirl stabilized gas flame model combustor and studied the heat release response characteristics of the swirl combustor through the flame transfer function. Firstly, the flame transfer function (FTF) was measured under different inlet velocities and equivalence ratios, and the experimental results showed that the FTF gain curve of the non-premixed swirl flame exhibited a significant “bimodal” shape, with the gain peaks located around 230 Hz and 330 Hz, respectively. Secondly, two oscillation modes of the flame near the two gain peaks were identified (the acoustic induced vortex mode Mv and the thermoacoustic oscillation mode Ma), which have not been reported in previous studies on swirl non-premixed flames. In addition, we comprehensively analyzed the flame pulsation characteristics under the two oscillation modes. Finally, the coupling degrees between velocity fluctuations, fuel pressure fluctuations, and heat release fluctuations were analyzed using the Rayleigh Index (RI), and it was found that in the acoustic-induced vortex mode, a complete feedback loop was not formed between the combustor and the fuel pipeline, which was the main reason for the significant difference in the pressure fluctuation amplitude near 230 Hz and 330 Hz.

Gas Turbine Combustion Technologies for Hydrogen Blends

The article reviews gas turbine combustion technologies focusing on their current ability to operate with hydrogen enriched natural gas up to 100% H2. The aim is to provide a picture of the most promising fuel-flexible and clean combustion technologies, the object of current research and development. The use of hydrogen in the gas turbine power generation sector is initially motivated, highlighting both its decarbonisation and electric grid stability objectives; moreover, the state-of-the-art of hydrogen-blend gas turbines and their 2024 and 2030 targets are reported in terms of some key performance indicators. Then, the changes in combustion characteristics due to the hydrogen enrichment of natural gas blends are briefly described, from their enhanced reactivity to their pollutant emissions. Finally, gas turbine combustion strategies, both already commercially available (mostly based on aerodynamic flame stabilisation, self-ignition, and staging) or still under development (like the micro-mixing and the exhaust gas recirculation concepts), are described.

Effect of oxy-colorless distributed combustion of methane flame behaviour in a premixed gas turbine burner

NOX emissions and flame characteristics in gas turbine burners are a current issue. Different combustion methods are tested for the solution of NOX emissions. One of these methods is oxy-colorless distributed combustion. In this method, CO2 is used as a diluent instead of N2 gas in the air. In this way, nitrogen does not enter the combustion chamber and theoretically NOX emissions are planned to be zero. In this study, a premixed and swirl assisted gas turbine combustion chamber used experimentally was verified numerically. Analyzes were carried out by keeping 3 kW thermal power, 1 swirl ratio and 0.7 equivalence ratios constant. The oxy-colorless distributed combustion method was applied to the pure methane flame at different O2/CO2 ratios. Analyzes were carried out with the O2 ratio of 26%, 21%, 19%, 17% and 15% by volume. The results showed that the colorless distributed combustion conditions were achieved as the CO2 ratio increased. Thanks to the oxy-colorless distributed combustion method, almost zero NOX emissions have been achieved. In addition, as the O2 ratio in the oxidizer mixture decreased, a significant decrease in the flame temperature was detected. Thanks to this study, the effect of oxy-colorless distributed combustion conditions in a premixed and swirl supported combustion chamber was investigated.

Multi-aspect evaluation of a novel geothermal-driven trigeneration system for cooling, heat, and power generation

This paper presents a novel trigeneration process that utilizes geothermal fluid and a gas turbine to generate electricity, heat, and cooling. The trigeneration system comprises a gas turbine cycle, dual flash geothermal-organic Rankine cycle, cooling production unit, and heat and power generation unit. A comprehensive parametric study is conducted from energy, exergy, economic, and environmental perspectives to evaluate the proposed process. Thermodynamic analysis shows that the energy and exergy efficiencies of the system are 46% and 47%, respectively. The total exergy destruction of the process is calculated to be 147,006 kW, with the gas turbine cycle and combustor contributing the highest and second-highest exergy destruction ratios at 66% and 45%, respectively. Environmental analysis reveals that the indirect emission of the proposed structure is zero, and the total carbon dioxide emission is related to the flue gas of the gas turbine unit, amounting to 44,010 kgCO2/h. Considering the production capacity of the three products, the carbon dioxide footprint is determined to be 17.44 kgCO2/MJ. Furthermore, the economic analysis indicates that the total annual cost of the proposed scheme is 56,817,774 $. The production costs for cooling, electricity, and heating are 0.3 $/kg(CW,5℃), 0.073 $/kWhe, and 0.174 $/kgST, respectively. This comprehensive evaluation demonstrates the efficiency and feasibility of the trigeneration process, making it a promising option for sustainable power generation with minimal environmental impact.

Generation of Entropy Waves by Fully Premixed Flames in a Non-Adiabatic Combustor With Hydrogen Enrichment

Abstract Thermoacoustic combustion instability is a major concern in gas turbine combustors with hydrogen-enriched fuels. Unsteady combustion not only generates acoustic waves but it may also result in fluctuations of burnt gas temperature, referred to as entropy waves. They are convected by the mean flow through the combustor and can cause indirect combustion noise when they are accelerated at the exit. In this work, we demonstrate that entropy waves occur in a fully premixed burner due to unsteady heat transfer at the combustion chamber wall. This mechanism of entropy generation is often neglected in the literature. This work shows an additional mechanism in CH4-H2-air flames, through which entropy may be created even in the fully premixed case. This is due to differential diffusion which generates local fluctuations in equivalence and carbon-to-hydrogen ratios. An adiabatic flame temperature is defined based on these two quantities to examine the influence of differential diffusion on the generation of entropy fluctuations. The generation of entropy waves is investigated by applying system identification (SI) to time series data obtained from a broadband forced large eddy simulation (LES) coupled with a heat conduction solver. The entropy transfer function (ETF) and flame transfer function (FTF) identified with LES/SI are then compared to experimental data obtained with tunable diode laser absorption spectroscopy with wavelength modulation spectroscopy (TDLAS-WMS) for measuring temperature fluctuations, and the multimicrophone method, respectively. After validating the computational setup, the entropy frequency response is identified at various positions within the combustion chamber, and the effects of generation and convective dispersion of entropy waves are qualitatively investigated. We show that a fully premixed turbulent system may exhibit significant entropy waves caused by wall heat losses and differential diffusion of hydrogen.

Acoustic Boundary Conditions for Can-Annular Combustors

This paper derives and validates an analytical model for acoustic boundary conditions on a can-annular gas turbine combustion system composed of discrete cans connected to an open annulus upstream of a turbine. The analytical model takes one empirical parameter: a connection impedance between adjacent cans. This impedance is extracted from time-marching computations of two-can sectors of representative combustors. The computations show that reactance follows the Rayleigh conductivity, while resistance takes a value of order 0.1 as a weak function of geometry. With a calibrated value of acoustic resistance, the analytical model reproduces can-to-can transfer functions predicted by full-annulus computations to within 0.03 magnitude at compact frequencies. Varying the combustor–turbine gap length, both model and computations exhibit a minimum in reflected energy, which drops by 63% compared to the datum gap. A parametric study yields a design guideline for gap length at the minimum reflected energy, allowing the designer to maximise transmission from the combustion system and reduce damping requirements.

Numerical study on the combustion process in a gas turbine combustor with different reference velocities

The mixing and combustion processes under different reference velocities in a gas turbine combustor were numerically investigated using the Flamelet Generated Manifold (FGM) model based on the Reynolds Averaged Navier–Stokes (RANS) method. The flow and combustion fields show strong self-similarity except on the slow auto-ignition in the mixing layer between fuel-rich product and fresh air upstream of the flame stabilization position. The time-scale analysis was carried out to understand the combustion modes inside the combustor. In general, the residence time of the fuel-mixture is much longer than both the chemical time scale and the mixing time scale. Thus, the combustion properties in each sub-zone were dominated by the mean flow structures. Furthermore, the combustion process exhibits a mixing-controlled feature in total. However, partially premixed combustion still appears on the flame base. Most of the fuel was found to be oxidized in the primary zone and the intermediate zone; however, the slow oxidization reactions also play a non-negligible role on the whole combustion process. Finally, a sketch map on the space of mixture fraction and combustion efficiency was proposed to understand the mixing and oxidization experiences of the fuel mixture.

Effects of Variable Pressure Outlets for Array Jet Impingement Cooling With a Bidirectional Exit Air Scheme

Abstract Array jet impingement in conjunction with other cooling methods such as effusion cooling is used in gas turbine combustion zones to provide optimized cooling in the form of double wall cooling around a combustion chamber. Utilizing a transient liquid crystal (TLC) technique an experimental investigation into the effects of pressure gradients and single versus multiple exits for array jet impingement crossflow is evaluated in the form of a detailed heat transfer analysis. In this study, four pressure gradients to bias mass flow ratios as (1:1), (2:1), (3:1), and (1:0), two jet array configurations either inline or staggered with jet to jet spacings (x/D = y/D) of 1.4, 1.9, and 2.2, three jet to target distances (z/D) ranging from 2 to 4, and three Reynolds number from 5000 to 15,000 are considered. In total, a test matrix of 72 different performance conditions was evaluated. Results are presented as local and area averaged Nusselt number plots along with local heat transfer coefficient contours. Overall, Nusselt number decreases with increased (z/D) and increased pressure gradient bias toward a single exit from (1:1) to (1:0). There is also slightly better performance from inline jet array configurations compared to staggered configurations.

Techno-economic optimization and Nox emission reduction through steam injection in gas turbine combustion chamber for waste heat recovery and water production

Considering the persistent human need for electricity and fresh water, cogeneration systems based on the production of these two products have attracted the attention of researchers. This study investigates a cogeneration system of electricity and fresh water based on gas turbine (GT) as the prime mover. The wasted energy of the GT exhaust gases is absorbed by a heat recovery steam generator (HRSG) and supplies the superheat steam required by the steam turbine (ST). In order to produce fresh water, a multi-effect desalination (MED) system is applied. The motive steam required is provided by extracting steam from the ST. In order to reduce the environmental pollution of this cogeneration system, the steam injection method is proposed in the GT's combustion chamber (CC). This system is optimized by a multi-objective optimization tool based on the Genetic Algorithm (GA). The design variables include pressure ratio of compressor (CPR), inlet temperature of gas turbine (TIT), steam injection mass flow rate in the CC, HRSG operating pressure, HRSG evaporator pinch point temperature difference (PPTD), steam pressure of the MED ejector, ejector motive steam flow rate, number of MED effects, and return effect. The goals are to minimize the total cost rate (TCR), which includes the cost of initial investment and maintenance of the system, the cost of consumed fuel, and the cost of disposing of CO and NO pollutants, as well as maximizing the exergy efficiency. In the end, it is observed that the steam injection in the CC leads to the reduction of the mentioned pollutant index, and it is proposed as a suitable solution to reduce the pollution of the proposed cogeneration system.

Natural gas-hydrogen hybrid combustion retrofit method and practice for F-class heavy-duty combustion engines

In order to reduce carbon emissions, enhance the operational flexibility of gas turbine power plants, and fill the gap in practical engineering transformation of natural gas-hydrogen blended combustion in heavy-duty gas turbines, a hydrogen blending retrofit was conducted on an F-class heavy-duty gas turbine combined heat and power unit. This served to examine the problems of combustion chamber tempering, combustion pulsation, and NOx emission increase caused by direct hydrogen-doped combustion in the combustion chamber. In this paper, the gas turbine body and hydrogen mixing system were reformed respectively. Retrofit schemes were proposed that were suitable for two operating conditions: 5%–15% and 15%–30% hydrogen blending. Experimental tests were conducted as a means of evaluating the performance of the retrofitted gas turbine and its compatibility with the boiler and steam turbine. The results of the retrofit showed there to be stable combustion, and there was no significant increase in average burner temperatures or occurrence of flashback. The gas turbine power output mostly remained unchanged and NOx emissions met the regulatory standards. The waste heat boiler flue gas temperature was controlled within the range of 84.9–88.2 °C, meaning that the safe operation of the steam turbine was not affected. The hydrogen blending rate was 0.2 Vol%/s, which indicates a smooth and precise control of the hydrogen blending process. It was estimated that the annual reduction in CO2 emissions would be 11,000 tons and 28,400 tons following respective hydrogen blending at 15% and 30%. A reliable retrofit scheme for hydrogen blending in gas turbines based on practical engineering transformation is presented in this study, which has significant reference value.

Synergistic effect of non-thermal plasma and CH4 addition on turbulent NH3/air premixed flames in a swirl combustor

The synergistic effect of non-thermal plasma (NTP) induced by a dielectric barrier discharge (DBD) and CH4 addition on turbulent swirl-stabilized NH3/air premixed flames in a laboratory-scale gas turbine combustor is experimentally investigated by varying the mixture equivalence ratio, φ, the mixt velocity, U0, and the mole fraction of CH4 in the fuel, Xf,CH4. It is found that the streamer intensity is significantly increased by adding CH4 to NH3/air flames compared with that by adding H2. This is because positive ions generated by CH4 addition play a critical role in generating streamers. Such streamers intensified by CH4 addition enhance the ammonia combustion more together with CH4, and hence, the lean blowout (LBO) limits of NH3/CH4/air flames are significantly extended compared with those without applying NTP. The maximum streamer intensity is found to be linearly proportional to φ⋅Xf,CH4⋅U0 in wide ranges of φ, Xf,CH4, and U0. NTP is also found to significantly reduce the amount of NOx and CO emissions simultaneously. All of the results suggest that NTP can be used more effectively with CH4 addition to stabilize turbulent premixed NH3/air flames and reduce NOx/CO emissions, which is attributed to their synergistic effect on the ammonia combustion.

Prediction model of NOx emissions in the heavy-duty gas turbine combustor based on MILD combustion

A prediction model of NOx emissions in heavy-duty gas turbine combustors based on the moderate and intense low-oxygen dilution (MILD) combustion was proposed, and the inlet parameter sensitivity analysis was also investigated to identify the impact weight for the practical operation of heavy-duty gas turbines. The optimal space-filling (OSF) design was first adopted to determine the optimal combination of gas temperature (Tgas), primary air temperature (Tfirst), secondary air temperature (Tsecondary), gas mass flow (mgas), primary air mass flow (mfirst), and secondary air mass flow (msecondary) for minimum NOx emissions. Based on the results of the OSF design, the minimum NOx emissions of 24.11 mg/m3 were obtained, and the corresponding Tgas, Tfirst, Tsecondary, mgas, mfirst, and msecondary were 769.67 K, 825.10 K, 722.61 K, 1.71 kg/s, 4.29 kg/s, and 7.69 kg/s within the range of 10% fluctuation of rated input parameters. The sensitivity ranking of the six inlet parameters was secondly achieved as mfirst > Tfirst > Tsecondary > msecondary > mgas > Tgas with the base of NOx emissions. Finally, a novel prediction model with six inlet parameters was established to quickly and accurately calculate the NOx emissions influenced by complicated boundary conditions in MILD combustion of heavy-duty gas turbines.

Life cycle assessment of a micro-region Hungarian municipal solid waste: Evaluation of six waste-to-energy scenarios

Waste-to-energy technologies are key to a sustainable future. The non-recyclable share is often converted to refuse-derived fuel (RDF) for energy utilization to landfill only about 10% of the initial volume. The composition of such fuels may significantly vary; therefore, the currently investigated samples were compared to several others available in the literature and found to be internationally representative. Then six different waste-to-energy scenarios were evaluated, suitable for a Hungarian micro-region: steam turbine, external combustion gas turbine, Organic Rankine Cycle with both direct and indirect fuel use, gas turbine, and internal combustion engine. The first three incinerated RDF, while the last three utilized pyrolysis gas of RDF. The thermal cycle of all six scenarios was evaluated first, followed by their assessment of the energy efficiency factor of the recovery, R1, mandated by the European Parliament and of the Council in Annex II of Directive 2008/98/EC on waste. It was concluded that the R1 threshold of 0.65 was only fulfilled by the gas turbine and the internal combustion engine. Finally, the environmental impact of the systems is addressed via life cycle assessment. The results were normalized and weighted to end up with a single score to facilitate decision-making, which is a novel approach in the field of WtE system assessment. The steam turbine, the gas turbine, and the internal combustion engine were all relatively efficient thermal cycles, resulting in a very similar positive impact with a mean of 321 person equivalent. This measure of the two Organic Rankine Cycle scenarios and the external combustion gas turbine was 639 person equivalent.

Sequence2Self: Self-supervised image sequence denoising of pixel-level spray breakup morphology

Optical imaging of fast and transient phenomena such as the turbulent breakup of liquid sprays exhibit low signal-to-noise ratios due to the limited illumination intensity relative to the short exposure time. Image denoising is required to facilitate physical studies over these data but is challenging due to the absence of clean ground-truths and the stringency of the denoising task (e.g., strong and complex noise, limited resolution, preserving physical fidelity), preventing supervised and existing un-/self-supervised deep learning methods. To this end, Sequence2Self (Seq2S) is proposed, an extension of Self2Self (S2S) to image sequences that leverages both the signal’s spatial and temporal correlation. Seq2S is demonstrated on time-resolved x-ray phase contrast imaging of liquid jet fuel sprays in a gas turbine combustor, which possesses all of challenges detailed above. Experiments are conducted across four fuels with different breakup morphology using various state-of-the-art methods. Overall, many of the methods failed and Seq2S was most successful: (1) Accurate spray structures were reconstructed with consistent evolution across frames void of artifacts. (2) The performance was robust, invariant to the hyperparameter choice. (3) Computational time is short and can be made eligible for real-time denoising. In particular, the images denoised by Seq2S showed spray droplet diameter distributions with near-zero Kullback–Leibler divergence (0.01 ± 0.01) to a cleaner reference, whereas the second best method yielded 0.06 ± 0.03. This suggests that Seq2S can be reliably used prior to subsequent quantitative spray analyses as it retains (if not, improves) the statistical physical properties of the data.

Spray ignition of n-alkanes in diesel and jet fuels: Effects of temperature, pressure, and N2 and NO addition

This study investigates the effects of NO-addition and N2-dilution on the autoignition process of n-C10–n-C14 alkanes, which are important components of diesel and kerosene-based jet fuels. The study is motivated by the need for a comprehensive understanding of the effects of nitrogen oxides (NOx) and N2 on the fuel ignition process. This understanding is essential to enable the effective employment of advanced combustion engine technologies, such as exhaust gas recirculation (EGR) and Rich-Quench-Lean (RQL) gas turbine combustors. Ignition delay time (IDT) measurements were performed under various combustion conditions relevant to practical engine operation and low-temperature oxidation chemistry in a constant-volume combustion spray chamber device. The experimental results show that N2-dilution consistently results in longer IDTs for the fuels tested. On the other hand, NO-addition has a temperature-dependent effect, shortening the IDTs for T > 692 K and vice versa. The magnitude of reactivity promotion or inhibition depends on NO concentration, temperature, pressure, and equivalence ratio. Based on the tested NO-addition levels, the inhibition of reactivity is approximately ten times greater than the promotion of reactivity caused by NO. The study fills a gap in the literature by providing comprehensive fundamental combustion data for n-C10–n-C14 fuels. This data, along with the corresponding analysis, can be used by engine researchers in developing more efficient and cleaner combustion engine technologies.

Fuel/air mixing characteristics of a Micromix burner for hydrogen-rich gas turbine

As a promising hydrogen-rich gas turbine combustion technology, Micro-mixing combustion may produce a new flame stabilization mechanism due to the novel structure. To investigate the effects of nozzle structural parameters and inlet aerodynamic parameters on mixing characteristics, this paper firstly used the background oriented schlieren technique combined with the self-development program to obtain the mixing quality, and the program was based on the optical flow method and Gladstone-Dale equation. The fuel-air mixture process was predicted by three mass diffusion models, and the Kinetic Theory model matched the experimental results best compared with the Constant Dilute Approximation model and Dilute Approximation model. The results showed that the main mixing zone moved closer to the outer wall when the premixed channel diameter increased. And the vorticity decreased with the increased premixed length, leading to a decline in mixing efficiency. For inlet aerodynamic parameters, changes in equivalence ratios only affected the shear-layer vorticity. As the combustible component of syngas was in the range of 60%–40% (by vol.), the outer wall of the premixed channel could promote fuel-air mixture. Moreover, when the equivalence ratio ranged in 0.335–0.685, the heating value of fuel varied as 4.686–7.029 and 11.715 MJ/Nm3, fuel and air were premixed uniformly near the nozzle outlet.

Computational Study of a Swirl Stabilized Flame in a Gas Turbine Combustor

Size of recirculation zone and temperature field is examined in a swirl stabilized aero gas turbine combustor using computational fluid dynamics. A sector of 22.5° of an annular combustor is modeled for the study. Unstructured tetrahedral meshes comprising 1.2x106 elements are employed in the model where the governing equations are solved using CFD flow solver CFX. Grid sensitivity study and code validation through limited test data has also been carried out. The effect of pressure and fuel-air ratio on the size of recirculation zone and apparent size of flame zone has been studied at steady state conditions. The heat release rate due to combustion is found to affect the length of recirculation zone as well as the velocity field inside the combustion liner.

Effect of Diffuser Geometry on the Performance of an Annular Aero Gas Turbine Combustor

Combustor is an important component of a gas turbine engine and its performance governs the overall performance of the engine. This paper describes the effect of diffuser geometry on the performance parameters of short annular combustors. Full-scale combustors having similar liner configurations but different diffuser geometry were tested in the combustor test facility for this investigation. The combustor aerothermal characteristics such as light-up behavior, exit temperature pattern factors and combustion efficiency are found to be inde- pendent of diffuser geometry. But the major aerodynamic parameters such as diffuser pressure loss, static pressure recoveries etc are significantly affected by the diffuser geometry.