Gas Turbine Combustion Chamber Research Articles

The Influence of Gas Fuel Enrichment with Hydrogen on the Combustion Characteristics of Combustors: A Review

Hydrogen is a promising fuel because it has good capabilities to operate gas turbines. Due to its ignition speed, which exceeds the ignition of traditional fuel, it achieves a higher thermal efficiency while the resulting emissions are low. So, it was used as a clean and sustainable energy source. This paper reviews the most important research that was concerned with studying the characteristics of hydrogen combustion within incinerators and power generation equipment, where hydrogen was used as a fuel mixed with traditional fuel in the combustion chambers of gas turbines. It also includes an evaluation of the combustion processes and flame formation resulting from the enrichment of gaseous fuels with hydrogen and partial oxidation. A large amount of theoretical and experimental work in this field has been reviewed. This review summarizes the predictive and experimental results of various research interests in the field of hydrogen combustion and also production.

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.

9E heavy-duty gas turbine ammonia-hydrogen mixture combustion characteristics and NOx emission characteristics research

In this study, we used the numerical simulation tool FLUENT to numerically simulate the combustion of ammonia-hydrogen fuel in the combustion chamber of a 9E heavy-duty gas turbine, and analysed the effects of different hydrogen blending ratios on the stability of ammonia combustion and NOx emissions. We found that an increase in the hydrogen mixing ratio in the fuel during the ammonia-hydrogen mixture combustion process contributes to the reduction of NOx emissions and has a positive effect on combustion stability.

Features of a gas turbine combustion chamber in operation with gaseous ammonia

Achieving climate neutrality requires the use of alternative hydrogen carriers for energy purposes, with ammonia currently being considered. One potential application in the energy sector is gas turbine systems, for which combustion chambers need to be designed to efficiently combust ammonia within an airflow. This paper focuses on theoretical investigations of fuel combustion completeness and environmental cleanliness of a gas turbine combustion chamber with a thermal power output of 1.0 MW, operating on gaseous ammonia. A prospective scheme for organizing processes is proposed, based on pre-mixing ammonia with a portion of air in a special pre-chamber, the sequential introduction of the remaining air through a radial-axial swirler and a series of holes in the flame tube, ensuring stable fuel combustion. Two approaches were used for modeling combustion processes in such a combustion chamber: one based on chemical reactor theory and the other on three-dimensional hydrodynamic analysis. After conducting a detailed kinetic analysis, it was concluded that to maintain stable ammonia combustion while varying the air excess coefficient in the primary combustion zone from 1.4 to 2.0, the reactants need to remain in this zone for a duration exceeding 0.025 s. Based on these parameters, design schemes for two combustion chamber variants were developed, differing in combustion tube length and air distribution pattern, for operation with an ammonia flow rate of approximately 50 g/s and a pressure of 0.3 MPa, determining a gas outlet temperature of 1490 K. Three-dimensional calculations of aerodynamic flow structures, ammonia combustion, and formation of toxic components were conducted, revealing that the proposed process organization scheme ensures complete ammonia combustion and small nitrogen oxide emissions. These results have potential applications in the development of new gas turbine combustion chamber designs for decarbonized energy systems, including those integrated with solid oxide fuel cells.

Experimental investigation of the effect of air/fuel ratio change on JP8 swirl flame characteristics with image processing methods

In this study, the stable combustion ranges and emission values of JP8 fuel, which is used in military aviation, were tested and optimum conditions were determined. The AFR (Air/Fuel Ratio) of the JP8 flame was increased experimentally at constant thermal power in a gas turbine combustion chamber. In the study, AFR were tested as 30/1, 33/1, 36/1, 39/1 and 42/1. A generator with 0.4 swirl number is placed at the burner outlet. Under these conditions, the effect of external acoustic enforcement frequencies on dynamic instabilities at different AFR was investigated. Flame length and thickness data were extracted from the images obtained from the image processing technique. The effect of AFR change on the combustion chamber temperature was examined and pollutant emissions were measured. The results showed that the most stable flame appeared in AFR 33/1 case at 155 and 300 Hz resonance frequencies under acoustic enforcements. Additionally, when the AFR was increased to 42/1, flame instability increased at all frequency values. Moreover, it has been determined that the most optimum mixture in terms of combustion chamber exit temperature and CO emissions is AFR 33/1. There was an increase in NOX emissions by up to 39/1 with the increase in AFR.

Thermo-elastic Characteristics of Thermal Barrier Coating in a Gas Turbine Combustion Chamber with an Intermediate FGM Layer

This study is focused on the analysis of thermos-elastic characteristics of a gas turbine combustion chamber, where the inner surface experiences a higher temperature while the outer region of the wall should be thermally conductive to dissipate the heat of combustion. Using a single material is not suitable to ensure the above two requirements simultaneously. Instead of using a single material, a layered combustion chamber with high-temperature material at the inner region and thermally conductive material at the outer region can be a solution. This produces the problem of a sharp interface where disbonding occurs due to high thermal stresses. The problem of sharp interface can be eliminated by using a functionally graded material (FGM) layer in between the inner and outer layers of the combustion chamber. The present study considers a gas turbine combustion chamber consisting of three layers: the inner layer is used as a thermal barrier coating, the intermediate layer is a smooth transition from the inner layer to the outer layer, and the outer layer is a thermally conductive material. ANSYS simulation is used for the analysis of thermos-elastic characteristics of the combustion chamber with homogeneous and FGM intermediate layers. The effect of linear and nonlinear material distributions in the FGM layer on the thermos-elastic characteristics is studied. A comparison of results reveals that thermal stress smoothly changes from the inner layer to the outer layer in the case of the FGM intermediate layer compared to the homogeneous intermediate layer. This suggests that a combustion chamber with an FGM intermediate layer is more reliable than a homogeneous intermediate layer.

Numerical investigation on mixing of heated confined swirling coaxial jets with blockage

Abstract A coaxial jet that has one application in gas turbine combustion chambers where there is a requirement for very good mixing of air and fuel for complete and stable combustion. A study has been carried out to improve the mixing of annular and central jets in the confined space of the combustor. The combustor model is used with two confined coaxial air-swirling jets under non-combustion conditions. The influence of a heated central jet and the effect of blockage at different locations in confined spaces on mixing has been studied. To understand mixing in jets in confinement, the center line axial velocity profile and streamlines have been presented at different locations. The computational results are obtained using commercial CFD software, ANSYS FLUENT 18.0, with a standard k–ω turbulence model. After validation with the existing literature, parametric studies have been carried out with co-swirl and counter-swirl conditions of annular and central jets at different blockage locations in confinement. The results show a good understanding of the mixing process of two jets in confinement.

Effect of entropy waves on the thermoacoustic instability of choked outlet combustion chambers

Thermoacoustic instability is a major issue in aero-engine and gas turbine combustion chambers, especially for the case of lean premixed combustion. The instability is caused by the interaction of acoustic waves with unsteady heat release. As considering the accelerated entropy waves in the system, the entropy effect on the acoustic waves cannot be ignored, which will further modify the thermoacoustic instability. Recent researches have shown that the entropy waves can be generated by the steady heat sources or temperature gradients, which can exclude the interference of unsteady heat release factors in instability analysis. In this study, the effect of entropy waves on the thermoacoustic instability of the combustion chamber model with choked outlets is investigated by constructing a low-order acoustic network model. New modes introduced by entropy waves, called as the entropy acoustic modes (EA modes), are investigated by a steady heat source. Then the unsteady heat release is considered, and the effect of entropy waves on different modes and the coupling behavior of these modes are analyzed comprehensively. It is found that some modes are jointly affected by the flame, entropy waves as well as the acoustic waves, which are called as the entropy thermoacoustic modes (ETA modes). Moreover, the modal frequencies of the intrinsic thermoacoustic instabilities modes (ITA modes) are changed remarkably due to the introduction of entropy waves. In addition, the entropy wave dispersion and dissipation show a non-negligible effect on the thermoacoustic instability.

Ignition Delay Times and Chemical Kinetic Model Validation for Hydrogen and Ammonia Blending With Natural Gas at Gas Turbine Relevant Conditions

Abstract Ignition delay times from undiluted mixtures of natural gas (NG)/H2/Air and NG/NH3/Air were measured using a high-pressure shock tube at the University of Central Florida. The combustion temperatures were experimentally tested between 1000 and 1500 K near a constant pressure of 25 bar. As mentioned, mixtures were kept undiluted to replicate the same chemistry pathways seen in gas turbine combustion chambers. Recorded combustion pressures exceeded 200 bar due to the large energy release, hence why these were performed at the high-pressure shock tube facility. The data are compared to the predictions of the NUIGMech 1.1 mechanism for chemical kinetic model validation and refinement. An exceptional agreement was shown for stoichiometric conditions in all cases but strayed at lean and rich equivalence ratios, especially in the lower temperature regime of H2 addition and all temperature ranges of the baseline NG mixture. Hydrogen addition also decreased ignition delay times by nearly 90%, while NH3 fuel addition made no noticeable difference in ignition time. NG/NH3 exhibited similar chemistry to pure NG under the same conditions, which is shown in a sensitivity analysis. The reaction CH3 + O2 = CH3O + O is identified and suggested as a possible modification target to improve model performance. Increasing the robustness of chemical kinetic models via experimental validation will directly aid in designing next-generation combustion chambers for use in gas turbines, which in turn will greatly lower global emissions and reduce greenhouse effects.

Theoretical study on the inherent relationship between laminar burning velocity, ignition delay time, and NO emission of ammonia-syngas-air mixtures under gas turbine conditions

This study utilizes numerical methods with Chemkin 19.2 and Matlab R2020a to investigate the relationship between laminar burning velocity and free radical concentration, the relationship between laminar burning velocity and ignition delay time, and the relationship between NO emissions and free radical concentration for ammonia-syngas-air combustion. Additionally, it explores the mechanisms by which these three relationships change with variations in the initiate temperature and chamber pressure of the combustion chamber. Furthermore, to understand the theoretical foundation of these relationships, the study examines four global flame parameters: adiabatic flame temperature (Tad), activation energy (Ea), Zeldovich number (Ze), and Lewis number (Le). The results indicate that changes in initial temperature and pressure influence the laminar burning velocity by modifying the concentration of H + NH2 radicals. Simultaneously, alterations in initial temperature and pressure also adjust the quantitative relationship between laminar burning velocity and the concentration of H + NH2 radicals. Additionally, the results reveal that variations in initial temperature and pressure impact NO emissions by altering the concentration of H + NH2 radicals. Following a comprehensive examination of both the theoretical relationship between laminar burning velocity and ignition delay time and the empirical relationship between laminar burning velocity and ignition delay time, a relationship between the density-weighted collision rate BC in the laminar burning velocity expression and the pre-exponential factor A in the theoretical expression for ignition delay time was observed, where BC2A = C0∙Tuδ∙Pε (where C0, δ and ε are constants). This offers a potential methodology for investigating thermal effects, chemical effects, and transport effects in complex mixed fuel combustion processes. Further investigation demonstrates that an increase in the initial temperature within a gas turbine combustion chamber will, by promoting thermal effects, inhibiting transport effects, and altering chemical effects, affect the quantitative relationship between laminar burning velocity and ignition delay time. Further research reveals that an increase in the initiate temperature of the gas turbine combustion chamber affects the quantitative relationships between laminar burning velocity and ignition delay time by promoting thermal effects, suppressing transport effects, and chemical effects. An increase in chamber pressure influences these relationships by enhancing chemical and transport effects while inhibiting thermal effects. Moreover, the functions characterizing chemical effects, transport effects, and thermal effects can be reasonably approximated in this study as functions of initial temperature and pressure, especially under the specific F-class gas turbine conditions presented herein. This finding holds significance for the design of combustion chambers under actual gas turbine operating conditions.

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.

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.

Comparative analysis of ammonia/hydrogen fuel blends combustion in a high swirl gas turbine combustor with different cooling angles

In this study, numerical modeling of ammonia-hydrogen fuels (10%–50%) in a turbulent eddy gas turbine combustion chamber with different cooling angles (15, 30, 45) have been performed by using a computational fluid dynamics code. It has been observed that the maximum temperature levels in the combustion chamber decrease with the addition of ammonia and the flame moved towards the exhaust of the combustion chamber because of the lower burning rate of ammonia in the regions where the flame occurs. Although the addition of ammonia in the combustor increases the NOx levels in the flame core rapidly. The 45° provides a more homogeneous temperature distribution compared to other conditions with 15–30° inclination angles at the outlet. As a result, it can be concluded that ammonia-hydrogen blended fuels have a substantial possibility as an option and sustainable fuel in terms of combustion performance.

Wall heat loss effect on the emission characteristics of ammonia swirling flames in a model gas turbine combustor

Ammonia (NH3) combustion is regarded as one of the most promising solutions to realize zero CO2 emission. However, its low reactivity, low heat release result in a strong thermal effect (wall heat loss effect) which significantly affects flame macro structure and NOx emission characteristics. In this study, an air film cooling on the swirling combustion chamber was designed to investigate the wall heat loss effect on NOx emission. The flame structure and NO production were measured with the OH-/NO-PLIF techniques. The NOx emission was analyzed by the Gasmet DX4000 Fourier Transform Infrared (FTIR) gas analyzer. Large eddy simulation was also conducted with detailed chemistry to extend the understanding of the experimental findings. For the current combustion chamber, a larger convection heat loss was obtained when increasing the cooling air flow rate. NO emission shows a decreasing trend with heat loss which is mainly caused by the chemical reactions at near all region. This can be verified by the relatively farther NO profile from the combustor wall. By analyzing the LES results at near all region, the combustion efficiency is decreased due the lower temperature. As a result, NO production from HNO and NH pathway is suppressed due to the local OH decreasing in near-wall region. The larger unburned NH3 in the exhausted gas may also consumes NO by the NO reduction reactions. In comparison, N2O, around 300 times global warming potential than that of CO2, significantly increases as the heat loss increases. This is mainly because that the production of N2O from NO is promoted and N2O decomposition is suppressed within the thermal boundary. This study suggests that N2O might become a more serious emission component in NH3 fueled gas turbines. Furthermore, the heat loss effect on the NOx production should be fully considered when designing the gas turbine combustion chamber with strong wall cooling.

Analysis of CO2 capture process from flue-gases in combined cycle gas turbine power plant using post-combustion capture technology

Combined cycle gas turbine power plants (CCGTs) are a combined cycle consisting of a gas turbine and a steam turbine to generate electricity. Sometimes CCGTs incorporate cogeneration to produce both heat and power. After the gas fuel combustion in the gas turbine combustion chamber, the flue gases are passed through the Heat Recovery Steam Generator (HRSG) to extract heat and generate additional electrical power using the steam turbine. The CCGT technology is recognized for its highest efficiency of 58% in electricity production among the power production technology. A highly efficient CCGT power plant with 60% efficiency produces even 2.5 times less CO2 than a modern coal power plant with an efficiency of 45% because of the use of gas fuel and electrical efficiency. The CO2 emission can be reduced further when the post-combustion CO2 capture methods are applied. To perform CO2 capture and to reduce the CO2 emission from power plants, the CO2 mass fraction in flue gas is the crucial parameter for the operation of the Post-combustion Carbon Capture and Storage (PCCS) technology. The PCCS technology uses solvents, which is the aqueous solution of amine that reacts with flue gas and absorbs the CO2, which is treated and separated later. The paper presents the results of the energy analysis of a post-combustion carbon capture process when integrated with a combined cycle gas power plant. The study considered two different gas fuels such as methane and syngas. Syngas composition was determined from the sewage sludge gasification process and can be treated as zero-emission CO2 gas fuel. When the flue gas produced from the syngas is used in PCCS at more than 50% of load conditions, the negative CO2 emission level in large-scale CCGT power plants can be reached. The paper presents the results of mass and energy balance analysis of HRSG of a CCGT integrated with PCCS to perform CO2 capture. The analysis of HRSG using flue gases from methane and syngas is performed by calculating the enthalpy of flue gas, rate of heat exchange, and temperature distribution of each component of HRSG. The comparison of the result shows slight differences due to the different composition and flow rates of flue gases. The flue gas at the outlet of two HRSG is used in the PCCS at different load conditions. An aqueous solution of 30 wt% Monoethanolamine (MEA) with rich loading of 0.5 mol-CO2/mol-MEA and a mixture of 16 wt% 2-amino-2-methyl-1-propanol (AMP) – 14 wt% Piperazine (PZ) with rich loading of 0.62 and 0.86 mol-CO2/mol-amine respectively are used in the PCCS. Due to the reboiler duty of amines, the steam consumed by the PCCS for AMP-PZ regeneration is less compared to MEA. Depending upon the flue gas and solvent used in the PCCS, the power consumed by the PCCS from CCGT power plant is measured from 9.6% to 11.6%. For the given operating condition of the CCGT and PCCS at more than 50% load condition, the negative CO2 emission level can be achieved.

Application of Biogas from Quinoa, Wheat, and Andean Guinea Pig Residuals as Biofuels for Gas Turbines

This article shows the effect that biogases obtained from crop residuals from the Andean region have on the performance of a whole medium-sized electrical-generating gas turbine. This technology could be used to supply electricity in energy-depressed areas where biogas is the only accessible resource. The gas turbine worked with higher efficiencies when the obtained biogases were used compared to natural gas. The biofuel that presented the highest efficiencies was the one obtained from wheat residuals alone. Despite this fact, this biofuel would be the most prone to create aerodynamic problems in the stages of the gas turbine. In this work, it was found that the addition of guinea pig manure to different crop residuals created biofuels less prone to create aerodynamic problems in the compression and expansion stages. In particular, the studied biofuel that had the most similar aerodynamic behavior to the design natural gas case was the one obtained from guinea pig manure and quinoa residuals. On the other hand, this biogas presented the lowest efficiencies of the studied biofuels. Despite this fact, this biofuel showed higher efficiencies than the natural gas case. In the gas turbine combustion chamber, all the studied biofuels operated at lower temperatures than the ones with natural gas, even in the high-power range. This would be an important feature for the running of the combustion chamber and the high-pressure turbine superalloys.

Combustion performance of plasma-stabilized lean flames in a gas turbine model combustor

This work presents an experimental study of the stabilization of lean methane-air flames by nanosecond repetitively pulsed (NRP) discharges. The experimental facility consists of a gas turbine model combustor with a Lean-Premixed-Prevaporized injector. The working pressure is 1 atm. The fuel is injected through two stages, each stabilized by swirl. The main stage consists of a multipoint annular injection. This facility is representative of a single sector of a gas turbine combustion chamber. The NRP discharges significantly extend the lean blow-off limit for a wide range of operating conditions, down to an equivalence ratio of 0.16. Lean flame stabilization is demonstrated for flame thermal powers up to 100 kW, with an electric power of less than 0.2% of the flame thermal power. We also observe plasma-assisted lean flames emiting less NOX than the leanest stable flames without plasma. Finally, by exploring the application of various pulse patterns instead of applying the discharges continuously at a constant repetition frequency, the plasma-to-flame power ratio required to stabilize a lean flame is decreased to 0.06% and the pollutant emissions can be further decreased.

Investigation of the Efficiency of a Dual-Fuel Gas Turbine Combustion Chamber with a Plasma‒Chemical Element

Abstract The study is devoted to the possibility of increasing the efficiency of the working process in dual-fuel combustion chambers of gas turbine engines for FPSO vessels. For the first time, it is proposed to use the advantages of plasma‒chemical intensification of the combustion of hydrocarbon fuels in the dual-fuel combustion chambers, which can simultaneously operate on gaseous and liquid fuels. A design scheme of a combustion chamber with a plasma‒chemical element is proposed. A continuous type mathematical model of a combustion chamber with a plasma‒chemical element has been developed, which is based on the solution of a system of differential equations describing the processes of chemical reactions in a turbulent system, taking into consideration the initiating effect of the products of plasma‒chemical reactions on the processes of flame propagation. A modified six-stage kinetic scheme of hydrocarbon oxidation was used to simultaneously predict the combustion characteristics of the gaseous and liquid fuels, taking into account the decrease in the activation energy of carbon monoxide oxidation reactions when the products of the plasma‒chemical element are added. The results reveal that the addition of plasma‒chemical products significantly reduces CO emissions in the outlet section of the flame tube (from 25‒28 ppm to 3.9‒4.6 ppm), while the emission of nitrogen oxides remains practically unchanged for the studied combustion chamber. Further research directions are proposed to enhance the working process efficiency of a dual-fuel combustion chamber for gas turbine engines as part of the power plant of FSPO vessels.

4E Transient Analysis of a Solar-Hybrid Gas-Turbine Cycle Equipped with Heliostat and MED

The current study investigates a cogeneration cycle of power and freshwater integrated with a solar system. The solar system is of the heliostat type, which is considered to preheat the inlet air in the combustion chamber of a 25-MW gas turbine. The waste heat of the turbine output stream is used to produce freshwater. Parameters such as the ambient temperature and solar irradiance significantly affect the system’s performance; hence, all analyses, including those pertaining to energy, exergy, economics, and environment, were conducted transiently, with a one-hour time step throughout the year so that the impacts of these effective parameters could be examined. Besides the analysis assuming a constant mass flow rate for the air entering the compressor, the calculations were repeated with the assumption of a constant volumetric flow rate to evaluate the cycle in the same conditions as those of natural gas power plants. Given the constant volumetric flow rate, for every 10-degree increase in temperature, the compressor power consumption decreased by approximately 2%. Moreover, a sensitivity analysis of the cycle performance in terms of ambient temperature was performed, and the corresponding results are presented. Finally, some correlations are presented to estimate variations in compressor power consumption and net turbine power due to temperature variations. The results demonstrate that in Bushehr, Iran, every one-degree increase in ambient temperature leads to an approximately 0.67 percentage decrease in net-generated power. In the end, the performance of the cycle was investigated under climatic conditions and solar irradiation intensities in several cities in Iran and some cities in different countries in which heliostat power plants have already been established. The results obtained in these cities were compared; it was concluded that the lowest annual cost of electricity generation is related to Isfahan in Iran, which reduces the cost of electricity generation by more than 20% (2.32 Cents/kWh) compared to the base cycle.

Synergistic effects of nanosecond plasma discharge and hydrogen on ammonia combustion

Synergistic effects of nanosecond plasma discharge and hydrogen on the combustion characteristics of ammonia/air are numerically studied under conditions relevant to gas turbine combustion chambers. It is shown that increasing the plasma contribution in assisting the flame results in lower NOX emissions by up to 27% than those in flames assisted by hydrogen for the range of operating conditions considered in this study. Plasma makes the consumption speed of the reactants less prone to the strain rate than that in flames assisted by hydrogen. It is found that discharging plasma with the pulse energy density of 9 mJ/cm3 alongside using 12% hydrogen by volume in the fuel increases the flame speed of ammonia/air to those of conventional fossil fuels such as methane—an improvement that is not achievable by just using hydrogen, even at a high concentration of 30%. Furthermore, raising the pulse energy density beyond a specific value broadens the reaction zones by generating radical pools in the flame preheating zone, which is expedited in fuel-rich conditions with high H2 fuel fractions. Investigations show that the simultaneous utilization of high-energy plasma and hydrogen reduces the NOX emissions by activating the mechanisms of nitrogen oxide denitrification (DeNOX) in preheating and post-flame zones, being more significant under the lean condition as compared with rich and stoichiometric cases. It is shown that increasing mixture pressure significantly deteriorates the impacts of plasma on combustion. Such unfavorable effects are weakly controlled by changes in the reduced electric field caused by pressure augmentations.