Water and steam injection in micro gas turbine supplied by hydrogen enriched fuels: Numerical investigation and performance analysis

This paper investigates the energetic and environmental performance of micro gas turbine plant with two proposed concurrent improvements: the methane-based fuel enriched by hydrogen and the humidification of the plant cycle. The energetic and environmental benefits of both features are well-know, and the aim of this work is the analysis of their combined impact on the micro gas turbine operation. Despite enhancing fuel with H₂ involves significant advantages like greenhouse emission reduction and a better combustion in case of low LHV fuels, most of commercial micro gas turbine combustors are not able to burn fuels with high hydrogen content unless structurally modified. On the contrary, has been demonstrated that humidified gas turbines (i.e., gas turbines with water injection, humid air turbine (HAT) and steam injection gas turbine (STIG) cycles) improve the combustion stability as well as electric power delivered and plant efficiency. Hence, in order to investigate the feasibility of the concurrent two features, the first step of this work was the thermodynamic analysis of a micro gas turbine supplied by methane-based fuels enriched with H₂ up to 20%_vol, considering both dry and humidified cycles. Since a combustion anomaly was detected, i.e., flashback, in the CFD study on the combustion chamber, a steam injection in the combustor has been added in the plant layout with the aim of overcoming the anomaly, and its effect on the combustion process has been analyzed also raising the hydrogen content up to 30%_vol. The main outcome of this paper is the assessment of the feasibility of supplying the combustor of the proposed HGT-STIG micro gas turbine with a hydrogen enrichment up to 30%_vol, achieving a safe and regular combustion mainly owing to a steam injection mass flow equal up to 125% of fuel flow.     

Numerical investigation of combustion characteristics for hydrogen mixed fuel in a can-type model of the gas turbine combustor

Numerical simulations are performed to analyze the combustion characteristics of propane fuel mixed with different amounts of hydrogen in a can-type combustor. The volume fraction of the hydrogen fuel varies from 0% to 100% in the fuel mixture. The results indicate that the hydrogen enrichment of the fuel significantly affects the flow structure, mixture fraction, and combustion characteristics. An increase in the volume fraction of hydrogen significantly affects the mean mixture fraction distribution, promotes combustion, and increases the flame temperature and the width of the flammable range within the combustor. Therefore, the degree of temperature uniformity at the outlet of the combustor increases with hydrogen enrichment, corresponding to an increase of 49.64% in the uniformity factor. The hydrogen enriched fuel can also reduce the emissions of CO and CO₂, owing to the reduced amount of carbonaceous fuel.     

Development of online control system for elimination of backfire in a hydrogen fuelled spark ignition engine

Backfire is one of the major technical issues in a port injection type hydrogen fuelled spark ignition engine. It is an abnormal combustion phenomenon (pre-ignition) that takes place in combustion chamber and intake manifold during suction stroke. The flame propagates toward the upstream of the intake manifold from combustion chamber during backfire and thus can damage the intake and fuel supply systems of the engine, and stall the engine operation. The main cause of backfire could be the presence of any hot spot, lubricating oil particle's traces (HC and CO due to evaporation of the oil) and hot residual exhaust gas present in the combustion chamber during suction stroke which could act as an ignition source for fresh incoming charge. Monitoring the temperatures of the lubricating oil and exhaust gas during engine operation can reduce the probability of backfire. This was achieved by developing an electronic device which delays the injection timing of hydrogen fuel with the inputs of engine oil temperature (T_{lube oil}) and exhaust gas temperature (T_exh). It was observed from the experimental results that the threshold values of T_{lube oil} and T_exh were 85 °C and 540 °C respectively beyond which backfire occurred at equivalence ratio (φ) of 0.82. The developed device works based on the algorithm that retards the hydrogen injection to 40 ⁰aTDC whenever the temperatures (T_{lube oil} and T_exh) reached to the above mentioned values and thus the backfire was controlled. Delaying injection of hydrogen increased the time period at which only air is inducted during the early part of the suction stroke, this allows cooling of the available hot spots in the combustion chamber, hence the probability of backfire would be reduced.     

An overview on dry low NOx micromix combustor development for hydrogen-rich gas turbine applications

The paper presents a survey of the interactive optimization cycle at Aachen University of Applied Sciences, used for the development of a new low emission Micromix combustor module for application in hydrogen fueled industrial gas turbines. During the development process, experimental and numerical methods are applied to optimize a given baseline combustor with 0.3 mm nozzles with respect to combustion efficiency, combustion stability, higher thermal power output per nozzle and reduced manufacturing complexity.Within the described research cycle combustion and flow simulations are used in the context of parametric studies for generating optimized burner geometries and the phenomenological interpretation of the experimental results. Experimental tests, carried out on an atmospheric combustion chamber test stand provide the basis for validation of simulation results and proof of the predicted combustion characteristics under scaled down gas turbine conditions.In the presented studies, an integration-optimized Micromix combustor with a nozzle diameter of 0.84 mm is tested at atmospheric pressure over a range of gas turbine operating conditions with hydrogen fuel. The combustor module offers an increase in the thermal power output per nozzle by approx. 390% at a significant reduced number of injectors when compared to the baseline design. This greatly benefits manufacturing complexity and the robustness of the combustion process against fuel contamination by particles.During atmospheric testing, the optimized combustor module shows satisfactory operating behavior, combustion efficiency and pollutant emission level. Within the evaluated operating range, which correlates to gas turbine part-, full- and overload conditions, the investigated combustor module exceeds 99% combustion efficiency. The Micromix combustor achieves NO_x emissions less than 2.5 ppm corrected to 15 Vol% O₂ at the design point.Based on numerical analyses and experimental low pressure testing, a full-scale gas turbine combustion chamber is derived. High pressure testing in the auxiliary power unit Honeywell/Garrett GTCP 36–300 shows stable operation during acceleration of the engine, during IDLE and during load variations between IDLE and Main Engine Start (MES) mode. Throughout the investigated operating range, the combustion chamber generates low NO_x emissions under full-scale gas turbine conditions.     

燃气轮机燃料轴向分级燃烧室的数值分析

为改善燃气轮机燃烧室的火焰筒壁温较高以及污染物排放等问题,提出了在火焰筒的壁面增加二次燃料喷口的轴向分级燃烧模式。利用ANSYS CFX软件并根据化学反应机理计算和分析了燃气轮机轴向分级燃烧室的流场和温度场,并与非分级燃烧室的结果进行了比较。结果表明:增大二次燃料比例可以使火焰筒壁面温度降低、出口污染物质量分数及出口不均匀系数减小,但出口平均温度会随之降低,导致做功能力减小。过量空气系数会影响火焰筒壁温、出口平均温度与NO质量分数。合理的二次燃料比例区间取决于多个条件。     

Fundamental characterization of backfire in a hydrogen fuelled spark ignition engine using CFD and experiments

Backfire, an abnormal combustion phenomenon, in a hydrogen fuelled spark ignition (SI) engine was analyzed using computational fluid dynamics (CFD) and experimental tests. One of the main causes of backfire origin is the presence of any high temperature heat source including hot spot in the combustion chamber of the engine during intake process. A CFD based parametric study was carried out by varying the temperature of hot spot and its location in the combustion chamber of the engine in order to analyze their effects on backfire origin and its propagation in the intake manifold of the engine. The temperature of hot spot was varied from 800 K to till the temperature of backfire occurrence. The minimum temperature of hot spot at which backfire occurred was observed as 950 K and beyond. The probability of backfire occurrence increases with increase in hot spot temperature. The CFD simulations were also carried out by varying the location of hot spot (spark plug tip and exhaust valve) and the results indicate that the location of hot spot does not influence the characteristics of backfire but it affects the timing of its origin. The average backfire velocity is 230 m/s based on the average turbulent flame velocity during backfire propagation in the intake manifold and the value agreed reasonably well with the experimental observations of backfire propagation on the engine with the transparent intake manifold. Backfire propagation is under the category of deflagration based on its velocity (subsonic), and the maximum pressure gradient (<0.3 bar). The backfire phenomenon is characterized into three stages namely ignition delay for backfire, backfire propagation and its termination. The study results provide a better in-depth understanding of backfire origin and its propagation and would be helpful for developing a robust control strategy. Based on this study, it is recommended that the spark plug and exhaust valves of hydrogen fuelled SI engine should be customized in such a way that the temperature of spark plug tip and exhaust valves should not exceed 900 K during suction process in order to eliminate backfire occurrence.     

某型舰用燃气轮机燃烧室故障原因分析及排除

介绍了某型舰用燃气轮机燃烧室故障及检查结果,探讨了故障发生的原因,研究并实施了故障排除的措施。经过试验,证明了故障原因分析的正确性和排除措施的可行性。     

Co-firing hydrogen and dimethyl ether in a gas turbine model combustor: Influence of hydrogen content and comparison with methane

To promote the utilization of hydrogen (H₂) in existing gas turbines, dimethyl ether (DME) was used to co-fire with H₂ in a model combustor. The swirl combustion characteristics of DME/H₂ mixtures were measured under the varying H₂ content up to 0.7. The results show that the flow velocity elevates as the H₂ content increases, which is associated with the increased flame temperature. The OH level firstly increases and subsequently keeps nearly unchanged as the H₂ content increases. Meanwhile, the OH area nonlinearly increases with the increasing H₂ content. Moreover, the increasing H₂ content induces almost linearly decreased lean blowout limit (LBO), increased NO emission, and intensified combustion acoustics. Furthermore, the combustion characteristics of the 0.46DME/0.54H₂ mixture and CH₄ with the same volumetric heat value were compared. The 0.46DME/0.54H₂ flame displays lower LBO and higher NO emission than the CH₄ flame, which mainly results from the higher reactivity of 0.46DME/0.54H₂ mixture.     

Numerical analysis of the effect of the hydrogen composition on a partially premixed gas turbine combustor

Large-eddy simulations (LESs) of a hydrogen-enriched 1/3-scale GE7EA gas turbine combustor are conducted. Four different fuel compositions are employed to investigate the role of the CH₄/H₂ syngas composition on the resulting flame structure and pressure oscillations occurring inside the combustor. A comparison with the experimental data is conducted to validate the numerical results. First, imaging processing is performed using an Abel-inversion technique for the accumulated OH mass fraction showing good agreement with the experimental images. Then, the calculated velocity fields are successfully compared to the experimental (particle image velocimetry) results. The results show that the flame structure is readily altered when changing the syngas composition; this strongly affects the flow field and therefore the pressure oscillations inside the combustor. When the hydrogen composition is increased, the flame becomes shorter and thicker, and its effect on the outer recirculation zone is minimized. When the flame length approaches the radial length of the combustor under certain conditions, the flame periodically attaches to the rigid wall and the pressure oscillations inside the combustor become amplified. Overall, the LES combined with the multi-step kinetics successfully predicts the variation in the flow fields due to fuel composition changes and reveals the role of the syngas composition in the combustor.     

Hydrogen injection as additional fuel in gas turbine combustor. Evaluation of effects

Industrial gas turbines fuelled by fossil fuels have been used widely in power generation and combined heat and power for many years. However they have to meet severe _NOx${\mathrm{NO}}_x$, CO and _CO2${\mathrm{CO}}_2$ (greenhouse effect) emissions legislation in many countries. This paper reports a study on injection of small quantities of hydrogen in a hydrocarbon fuelled burner like additionally fuel to reduce the pollutants emissions. Hydrogen is injected in the primary zone, premixed with the air. Using this injection together lean primary zone, it is possible to reduce the _NOx${\mathrm{NO}}_x$ level while CO an HC levels remains approximately constant.     

Effects of spray characteristics on combustion performance of a liquid fuel spray in a gas turbine combustor

Spray characteristics like mean drop diameter and spray cone angle play an important role in the process of combustion within a gas turbine combustor. In order to study their effects on wall and exit temperature distributions and combustion efficiency in the combustor, a numerical model of a typical diffusion controlled spray combustion in a can‐type gas turbine combustion chamber has been made. A simple k–ϵ model with wall function treatment for near‐wall region has been adopted for the solution of conservation equations in carrier phase. The initial spray parameters are specified by a suitable PDF for size distribution and a given spray cone angle. A radiation model for the gas phase, based on modified first order moment method, and in consideration of the gas phase as a grey absorbing–emitting medium, has been adopted in the analysis. It has been recognized that an increase in mean drop diameter improves the pattern factor. However, the combustion efficiency attains its maximum at an optimum value of the mean diameter. Higher spray cone angle increases the combustion efficiency and improves the pattern factor, but at the same time, increases the wall temperature. Copyright © 1999 John Wiley & Sons, Ltd.     

The effects and characteristics of hydrogen in SNG on gas turbine combustion using a diffusion type combustor

Converting coal to natural gas may be one of the alternative solutions for satisfying the demand for natural gas. However, synthetic natural gas (SNG) has not been proven effective in natural gas-fired power plants. In this research, several combustion tests using a diffusion type combustor were conducted to determine the effect of hydrogen content in SNG on gas turbine combustion. Three kinds of SNG with different H₂ content up to 3%vol were used for the combustion tests. Even a small amount of hydrogen in SNG affects the flame structure: it shortened the flame length and enlarged the flame angle slightly. However, hydrogen content up to 3% in SNG did not affect the gas turbine combustion characteristics, which are emission performance and combustion efficiency. Due to a similarity with real gas turbine combustor conditions for power generation, a high pressure combustion test helped us verify the ambient pressure combustion tests conducted to determine the effect of hydrogen in SNG. In the high pressure combustion test, the pattern factors were identical even though the hydrogen content was varied from 0% to 3%.     

间接确定燃气轮机初温的研究

从经济性和技术上来比较,燃气轮机发电技术具有较大的优势,这些优势必将转为应用上的快速、大规模的发展。由于“西气东输”工程的逐步开展,在华东地区将建设一批大容量的燃气轮机电厂,是燃气轮机在我国发展的转折点[1]。然而燃气轮机在运行监测、状态分析、性能诊断等方面还有     

LDA在燃气轮机燃烧室流场测量中的应用

介绍了激光多普勒测速技术在燃气轮机燃烧室内部流场测试的应用，阐述了LDA的基本原理和模型燃烧室内光学路径的实现方法，同时作者利用双相位多普勒分析仪DualPDA (Cual Phase Doppler Anemometer)对模型燃烧室内部流场进行了二维冷态测试，获得了大量的原始数据，为深入研究燃烧室内部气流特性提供了实验基础。     

Experimental Study on the Dynamic Characteristics of a Gas Turbine Combustor Burning Syn-gas

The present study focused on the development of a full-scale gas turbine combustor burning syn-gas from the coal-based multi-production. The dynamic features of a variety of parameters of the combustor, such as temperature and pressure during the procedures of startup and thermal load shifting, were measured and analyzed. The frequency and power spectrum of pressure fluctuation were analyzed by applying FFT and 1D continuous MORLET wavelet methods. The results show that the pressure fluctuation has distinct patterns during startup and load-transition procedures. The relationship between these dynamic features and the stability, safety and efficiency of gas turbine combustors burning syn-gas are preliminarily discussed.     

Effect of water injection and spark timing on the nitric oxide emission and combustion parameters of a hydrogen fuelled spark ignition engine

One of the main problems with hydrogen fuelled internal combustion engines is the high NO level due to rapid combustion. Use of diluents with the charge and retardation of the spark ignition timing can reduce NO levels in Hydrogen fuelled engines. In this work a single cylinder hydrogen fuelled engine was run at different equivalence ratios at full throttle. NO levels were found to rise after an equivalence ratio of 0.55, maximum value was about 7500 ppm. High reductions in NO emission were not possible without a significant drop in thermal efficiency with retarded spark ignition timings. Drastic drop in NO levels to even as low as 2490 ppm were seen with water injection. In spite of the reduction in heat release rate (HRR) no loss in brake thermal efficiency (BTE) was observed. There was no significant influence on combustion stability or HC levels.     

Visualization of heat transfer distributions in a gas turbine scroll

To visualize heat transfer distributions in systems with complex internal geometries, an experimental technique using a combination of the transient method and the hysteresis effect of thermopaint was developed. A mercury compound based thermopaint was used as a temperature indicator. Features of the paint are its reusability and its hysteresis nature. Isothermal lines visualized by the thermopaint are preserved after the experiment by utilizing the hysteresis nature. Also heat transfer on those parts that are hidden behind other parts can be visualized. Effects of initial and air temperature on the measurement uncertainty were evaluated. With this method, local heat transfer coefficients were obtained on the model scroll of a single can type combustor. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(3): 229–242, 1998     

Reduction of a detailed reaction mechanism for hydrogen combustion under gas turbine conditions

The aim of this study is to find a reduced mechanism that accurately represents chemical kinetics for lean hydrogen combustion at elevated pressures, as present in a typical gas turbine combustor. Calculations of autoignition, extinction, and laminar premixed flames are used to identify the most relevant species and reactions and to compare the results of several reduced mechanisms with those of a detailed reaction mechanism. The investigations show that the species OH and H are generally the radicals with the highest concentrations, followed by the O radical. However, the accumulation of the radical pool in autoignition is dominated by HO₂ for temperatures above, and by H₂O₂ below the crossover temperature. The influence of H₂O₂ reactions is negligible for laminar flames and extinction, but becomes significant for autoignition. At least 11 elementary reactions are necessary for a satisfactory prediction of the processes of ignition, extinction, and laminar flame propagation under gas turbine conditions. A 4-step reduced mechanism using steady-state approximations for HO₂ and H₂O₂ yields good results for laminar flame speed and extinction limits, but fails to predict ignition delay at low temperatures. A further reduction to three steps using a steady-state approximation for O leads to significant errors in the prediction of the laminar flame speed and extinction limit.