Gas Turbine Combustor Burning Research Articles

Numerical analysis of flame stabilization for a steady premixed jet in vitiated coflow

Premixed staged combustion in gas-turbine combustors, where a premixed fuel–air mixture is injected into a hot vitiated environment, has promise for better emission control. In these hot environments that occur at high engine pressure, the flames may stabilize by a combination of autoignition and premixed flame propagation. In this work, a laminar and steady premixed jet in vitiated coflow was studied numerically to examine the stability behavior of such flames that are impacted by both autoignition and flame propagation. Simulations with detailed chemistry were used with boundary conditions matching previous experiments to understand the stability mechanisms. At the conditions studied, the laminar flame was lifted, with the region of highest heat release rates occurring downstream of the jet exit. However, non-zero heat release rates an order-of-magnitude below the maximum value were observed continuously to the jet exit. An energy budget analysis was conducted along streamlines through different portions of the flame. Streamlines flowing through relatively low heat release rate regions near the burner exit were only influenced by mixing between the jet and vitiated coflow. Streamlines which flowed through higher heat release rates in the lifted flame were influenced by heat transfer from both the coflow and the existing flame, leading to heat-transfer assisted propagating premixed-flame behavior. Species budgets analyzed in the low- and high-heat release regions of the flames were also used to characterize autoignition locations. The species budget through autoignition regions showed clear markers such as high CH2O concentrations present ahead of high heat release rates. The streamlines through premixed propagation regions of the flame also had high CH2O concentrations upstream of the high heat release region, but the species budget shows this is due to mixing from autoignition regions as opposed to reactions occurring on the streamline ahead of the flame. Thus, caution must be taken when using CH2O as a marker for autoignition in such flames with mixed stabilization modes.

A review on the applications of the chemical reactor network approach on the prediction of pollutant emissions

PurposeThe purpose of this paper is to review the applications of the chemical reactor network (CRN) approach for modeling the combustion in gas turbine combustors and classify the CRN construction methods that have been frequently used by researchers.Design/methodology/approachThis paper initiates with introducing the CRN approach as a practical tool for precisely predicting the species concentrations in the combustion process with lower computational costs. The structure of the CRN and its elements as the ideal reactors are reviewed in recent studies. Flow field modeling has been identified as the most important input for constructing the CRNs; thus, the flow field modeling methods have been extensively reviewed in previous studies. Network approach, component modeling approach and computational fluid dynamics (CFD), as the main flow field modeling methods, are investigated with a focus on the CRN applications. Then, the CRN construction approaches are reviewed and categorized based on extracting the flow field required data. Finally, the most used kinetics and CRN solvers are reviewed and reported in this paper.FindingsIt is concluded that the CRN approach can be a useful tool in the entire process of combustion chamber design. One-dimensional and quasi-dimensional methods of flow field modeling are used in the construction of the simple CRNs without detailed geometry data. This approach requires fewer requirements and is used in the initial combustor designing process. In recent years, using the CFD approach in the construction of CRNs has been increased. The flow field results of the CFD codes processed to create the homogeneous regions based on construction criteria. Over the past years, several practical algorithms have been proposed to automatically extract reactor networks from CFD results. These algorithms have been developed to identify homogeneous regions with a high resolution based on the splitting criteria.Originality/valueThis paper reviews the various flow modeling methods used in the construction of the CRNs, along with an overview of the studies carried out in this field. Also, the usual approaches for creating a CRN and the most significant achievements in this field are addressed in detail.

3D Simulation of Ammonia Combustion in a Lean Premixed Swirl Burner

To date, a number of mechanical, electrical, thermal, and chemical approaches have been developed for storing electrical energy for utility-scale services. The only sufficiently flexible mechanism allowing large quantities of energy to be stored over long time periods is chemical energy storage in the form of carbon or hydrogen. One chemical considered for hydrogen carriage that can potentially be employed for storage is ammonia. Ammonia can substitute pure hydrogen for storage and be employed for power generation at large industrial scale if the molecule is efficiently burned through mature equipment such as gas turbines, thus providing not only a carbon free fuel, but also a chemical capable of being stored at low energy requirements. Thus, progress on the use of ammonia in gas turbines is a main priority for groups working on the area. Studies need to be conducted in experimental rigs with strong CFD analyses for further industrial implementation. In this paper, modelling of ammonia combustion in a generic gas turbine combustor is explored in order to provide an effective tool for future application. Large Eddy Simulation approach was used to develop a model for ammonia/hydrogen combustion in gas turbine combustors. To capture more details of the turbulent reacting flow, a detailed chemical mechanism was selected for a deep insight. A Partially Stirred Reactor framework was utilized to deal with the turbulence/chemistry interaction. The developed model was then applied to the simulation of lean premixed ammonia/hydrogen flames in a generic swirl burner. A preliminary validation for the model is performed by correlation of NOx emission with experimental data. Results show the model can provide detailed information of flow field, flame structure, emissions, etc. It can be used to optimize the procedure of utilizing ammonia as a fuel in future equipment design.

Dynamic Characterization of a Ducted Inverse Diffusion Flame Using Recurrence Analysis

ABSTRACTNormal diffusion flame or partially premixed flame is used in many applications, such as aviation engines, tanks, ocean vessels, and industrial furnaces, because of its high flame stability and relatively low susceptibility to dynamic instabilities compared to lean premixed flames, which give lower emissions. However, associated with such flames are high NOx and soot emissions, which are particularly high for heavier hydrocarbon fuels. Increasingly stringent environmental norms have thus dictated the search for alternate approaches; one such being the inverse diffusion flame, which is currently being used in rocket motors, for staged combustion in gas turbine combustors, and furnaces. However, the dynamic response of such a flame, particularly in ducted applications where a coupling between unsteady heat release rate and duct acoustics may occur, is relatively less explored. The present work aims to plug that knowledge gap through an experimental investigation of a laboratory-scale ducted inverse diffusion flame. Two parametric variations of the flame were performed—variation of the flame position and variation of the air flow rate. Using tools of nonlinear dynamics, such as phase space reconstruction and recurrence quantification, several interesting dynamic characteristics were observed, such as limit cycles, intermittency, and homoclinic orbits. For a constant air flow rate, the system was observed to transition from a type-II intermittency regime to a limit cycle and then again to intermittent behavior as the position of the flame within the duct was varied. A similar trend was observed when the air flow rate was varied at a fixed flame position.

Experimental study of the gaseous and particulate matter emissions from a gas turbine combustor burning butyl butyrate and ethanol blends

This paper reports the gaseous pollutants and Particulate Matter (PM) emissions of a gas turbine combustor burning butyl butyrate and ethanol blends. The gas turbine has been tested under two operational conditions to represent the cruising (condition 1) and idling (condition 2) conditions of aero engines. Aviation kerosene RP-3 and four different biofuels using butyl butyrate (BB) and ethanol blends were tested and compared to evaluate the impact of fuel composition on CO, NOx, unburnt hydrocarbon (UHC) and PM emissions under selected two operational conditions. The PM number (PN) concentration and size distributions were measured by a scanning mobility particle sizer (SMPS). The compositions of filter borne PM were analysed by ion chromatograph technique. The concentrations of CO, NOx and UHC were detected and analysed by a gas analyser. Results indicated that under idling and cruising conditions the CO emissions from butyl butyrate and ethanol blends were higher than that of RP-3 due to the relatively lower combustion temperature of the biofuels compared with that of RP-3. Results of the NOx emission comparison indicated the biofuels produced less NOx than RP-3 and the increase of ethanol content in the biofuels could reduce the NOx and UHC emissions. The particles smaller than 20nm played a dominant role in PN emissions at condition 1 with the range from 2×106/cm3 to 4×107/cm3. There was a peak value of particle number concentration with the particle size ranging from about 25nm and 40nm. The PN emission index at condition 1 was higher than that at condition 2 for the biofuels, whilst the trend was opposite to that of RP-3. The ions analysis indicated Ca2+ and SO42− were the two dominant ions in the PM emissions of biofuels.

Prediction of soot and thermal radiation in a model gas turbine combustor burning kerosene fuel spray at different swirl levels

Combustion of kerosene fuel spray has been numerically simulated in a laboratory scale combustor geometry to predict soot and the effects of thermal radiation at different swirl levels of primary air flow. The two-phase motion in the combustor is simulated using an Eulerian–Lagragian formulation considering the stochastic separated flow model. The Favre-averaged governing equations are solved for the gas phase with the turbulent quantities simulated by realisable k–ϵ model. The injection of the fuel is considered through a pressure swirl atomiser and the combustion is simulated by a laminar flamelet model with detailed kinetics of kerosene combustion. Soot formation in the flame is predicted using an empirical model with the model parameters adjusted for kerosene fuel. Contributions of gas phase and soot towards thermal radiation have been considered to predict the incident heat flux on the combustor wall and fuel injector. Swirl in the primary flow significantly influences the flow and flame structures in the combustor. The stronger recirculation at high swirl draws more air into the flame region, reduces the flame length and peak flame temperature and also brings the soot laden zone closer to the inlet plane. As a result, the radiative heat flux on the peripheral wall decreases at high swirl and also shifts closer to the inlet plane. However, increased swirl increases the combustor wall temperature due to radial spreading of the flame. The high incident radiative heat flux and the high surface temperature make the fuel injector a critical item in the combustor. The injector peak temperature increases with the increase in swirl flow mainly because the flame is located closer to the inlet plane. On the other hand, a more uniform temperature distribution in the exhaust gas can be attained at the combustor exit at high swirl condition.

Biparametric assessment of the combustion stability in an industrial gas turbine combustor

Here we propose a generalized procedure for a two-parameter assessment of the Combustion stability (CS) of industrial gas turbines. In evaluating the CS, this procedure employs two parameters of measured dynamic pressure data: the Root-mean-square (RMS) pressure as the primary parameter and the damping ratio as a secondary parameter. The former tells the time-averaged level of the dynamic pressure, and, the latter, the degree of acoustic energy loss. A data point pairing the two parameters, which are evaluated at a specific instance of a combustion process, identifies Instantaneous combustion stability (ICS) by its location on a 2-D domain of both parameters. Collective representation of the ICS points on the domain produces a CS map of the combustion process. The locus of the ICS point on the map represents the temporal variation of CS during the combustion process. The biparametric assessment procedure divides the CS map into three regimes (i.e., stable, transitional and unstable) by utilizing two threshold values for the RMS pressure and one for the damping ratio. The feasibility of the proposed procedure was tested with the dynamic pressure data from a model gas turbine combustor burning synthetic natural gas. Then the technique was applied experimental data obtained from a laboratory-scale lean premixed combustor to identify the three regimes of the combustion process of a reported case. We found that the procedure is able to provide gas turbine operators with valuable information on CS during a combustion process, especially on the transitional regime.

Investigations of the Stabilities of Piloted Flames Using Blast Furnace Gas

The effective utilization of low-grade energy sources generated from steel-making processes provides not only excellent opportunities for low cost power generation but also a significant means for the reduction of greenhouse gas emissions. In this paper, the work was carried out to study the static and dynamic combustion instabilities for gas turbine (GT) combustors burning low-calorific-value blast furnace gas (BFG). A burner was designed to stabilize the BFG flame with central pilot flames. A diagnostic system was set up to detect the characteristics of flame dynamics. In the experiments, the fuel ratio between the pilot and main burner, and the equivalence ratio of the main flame and the annular flow velocity were varied for the investigation of the combustion lean blowout (LBO) limits. The flame dynamics near LBO were investigated. The dynamic responses of the flame to flow perturbations were also measured. A network model was employed to study and validate the blowout mechanisms. The LBO limits were calculated and compared with experimental results for various equivalence ratios.

Swirling flowfield for colorless distributed combustion

Distributed combustion has been shown to provide significant improvements of gas turbine combustors performance including uniform thermal field in the entire combustion chamber (improved pattern factor), ultra-low emission of NOx and CO, low noise, enhanced stability and higher efficiency. The flowfield associated with swirl is investigated to seek colorless distributed combustion. Non-reacting Particle Image Velocimetry (PIV) diagnostics is employed to determine the flow field characteristics of three different configurations with focus on velocity distribution, flow entrainment of reactive species, and turbulence. In all the configurations, air was injected tangentially into the combustor. The results for the configurations reported here represent both non-swirling “linear” flow and swirling flow. Results showed that swirling flowfield configuration is characterized by higher flow velocities and much enhanced entrainment ratios throughout the combustor as compared to non-swirling case. Swirling flow exhibited high velocity region at the core of the combustor to further promote mixing and entrainment of reactive species. Higher velocities and entrainment are of significant importance in distributed combustion to prevent flame anchoring and enhance mixing. Experimental results are compared with numerical simulation for seeking improved flow distribution. The flowfield for different configurations are integrated with earlier data on emissions that showed near zero emission for swirling distributed combustion in gas turbine combustors.

Advances in LES of Two-phase Combustion (II) LES of Complex Gas-Particle Flows and Coal Combustion

Large-eddy simulation (LES) is under its rapid development and is recognized as a possible second generation of CFD methods used in engineering. Large-eddy simulation of two-phase flows and combustion is particularly important for engineering applications. Some investigators, including the present authors, give their review on LES of spray combustion in gas-turbine combustors and internal combustion engines. However, up to now only a few papers are related to the state-of-the-art on LES of gas-particle flows and combustion. In this paper a review of the advances in LES of complex gas-particle flows and coal combustion is presented. Different sub-grid scale (SGS) stress models and combustion models are described, some of the main results are summarized, and some research needs are discussed.

Effects of Pressure on Prompt NOX Formation in CH4/Air Lean Premixed Flame

Since lean premixed combustion in gas turbine combustors undergoes in elevated pressure condition, it is important to know NOX formation characteristics under elevated pressure. Generally, effects of pressure on NOX formation characteristics are evaluated by using pressure coefficient on conventional systems. However, the value of pressure coefficient distributes widely from -0.2 to 0.5. This difference in the pressure coefficient stems from differences in experimental conditions and formation processes of NOX. As a result, effects of pressure on different NOX formation mechanisms have not been elucidated yet because of difficulties of temperature control of combustion region. In this study, to clarify the effects of pressure on the prompt NOX formation process is set as the objective. Experimental measurements and numerical simulation with detailed elementary reactions are conducted. The temperature controllable premixed flat flame burner is fabricated in the elevated pressure combustion chamber, and measurement of NOX concentration is conducted in the chamber. Both the experimental and numerical results clearly show that the pressure does not affect to the prompt NOX formation.

Effects of Unmixedness on Combustion Instabilities in a Lean-Premixed Gas Turbine Combustor

The present experimental study focuses on the effects of the degree of premixing and swirl strength on combustion instabilities occurring in a lean premixed gas turbine combustor burning natural gas and air. The combustor operated at pressurized conditions with heated air. Major measurements for the investigation of premixed combustion dynamics include pressure fluctuations, flame emissions in reacting flow, and acetone fluorescence in non-reacting flow to assess the degree of premixing between fuel and air. The acetone PLIF results revealed that the degree of premixing improves as mixing time increases. The first and second longitudinal acoustic modes were the dominant excited modes for most cases of interest. Combustion at a lean premixed condition becomes more susceptible to instabilities as the degree of premixing becomes poor, and self-excited pressure oscillations are obviously present under a fully premixed condition, even without equivalence ratio fluctuations in space. For incomplete premixing cases, local equivalence ratio fluctuations caused by poor premixing may initiate instabilities since reaction rate is sensitive to equivalence ratio fluctuations at lean conditions. Phase resolved chemiluminescence measurements show that pressure oscillations are strongly coupled with variations in flame structures.

Determination of Lean Burn Combustion Temperature Using Ultraviolet Emission

Measurements of the ultraviolet emission spectrum emitted from a lean burn premixed natural gas flame were taken over a range of flame temperatures using a fiber-optic/CCD spectrometer. Combustion temperatures were determined by two methods: by measuring the unburned oxygen in the exhaust and by calculating the temperature using the fuel and airflows. These temperatures were correlated to ratios composed of the integrated intensity of the long wavelength region of the OH band between 310 to 340 nm (ratio's numerator) and that between 305 and 310 nm (ratio's denominator). Average local combustor flame temperatures at the end of the combustion zone may then be determined by tracking these ratios during combustor operation. The sensitivity of these ratios yields a 0.8% change in the ratios every 20 degF with a precision of plusmn30 degF or plusmn1% at 3000 degF with 95 % confidence bounds demonstrating the feasibility of this technique for use as a potential control parameter for gas turbine combustors burning natural gas and air mixtures. This method is well suited for the low equivalence ratios (< 1) required to reduce NOx and CO emissions. Other methods using peak ratios of different emission bands exhibit nonlinearity, lower sensitivity and greater uncertainty.

LES studies of the flow in a swirl gas combustor

Environmental and other practical concerns have led to the development of compact gas turbine combustors burning lean mixtures leading to potentially low CO and NO x emissions. The compact design requires efficient atomization and mixing together with a compact premixed flame. Associated with these requirements are higher temperatures, increased heat transfer, and thermal load, thus increasing the danger of combustion instabilities (causing performance deterioration and excessive mechanical loads), and possible off-design operation. Numerical simulations of reacting flows are well suited to address these issues. To this end, large eddy simulation (LES) is particularly promising. The philosophy behind LES is to explicitly simulate the large scales of the flow and the thermochemistry, affected by boundary conditions whilst modeling only the small scales, including the interaction between the flow and the combustion processes. Here, we examine the flow and the flame in a model gas turbine combustor (General Electric’s lean premixed dry low NO x LM6000) to evaluate the potential of LES for design studies of engineering applications and to study the effects of the combustor confinement geometry on the flow and on the flame dynamics. Two LES models, a Monotone Integrated LES model with 1 and 2 step Ahrrenius chemistry, and a fractal flame-wrinkling LES model coupled to a conventional one-equation eddy-viscosity subgrid model, are used. Reasonable agreement is found when comparing predictions with experimental data and with other LES computations of the same case. Furthermore, the combustor confinement geometry is found to strongly affect the vortical flow, and hence also the flame and its dynamics.

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.

Combustion instability mechanism of a lean premixed gas turbine combustor

Lean premixed combustion has been considered as one of the promising solutions for the reduction of NOx emissions from gas turbines. However, unstable combustion of lean premixed flow becomes a real challenge on the way to design a reliable, highly efficient dry low NOx gas turbine combustor. Contrary to a conventional diffusion type combustion system, characteristics of premixed combustion significantly depend on a premixing degree of combusting flow. Combustion behavior in terms of stability has been studied in a model gas turbine combustor burning natural gas and air. Incompleteness of premixing is identified as significant perturbation source for inducing unstable combustion. Application of a simple convection time lag theory can only predict instability modes but cannot determine whether instability occurs or not. Low frequency perturbations are observed at the onset of instability and believed to initiate the coupling between heat release rate and pressure fluctuations.

Liquid-fuel/air premixing in gas turbine combustors: experiment and numerical simulation

Premixing of fuel oil and air for the purpose of lean-premixed combustion in gas turbine combustors was studied experimentally with laser-induced fluorescence (LIF) and numerically using a modified KIVA-3 code. A full-scale industrial burner, operated at atmospheric pressure, was investigated as well as a test burner of reduced scale, operated at pressures up to 15 bar. Three improved-accuracy models were used in the simulations to replace the corresponding standard KIVA-3 models: (1) a droplet-vaporization model including multiple components and real-gas effects; (2) a droplet-dispersion model, using a linear filter; and (3) a swirl correction to the k-ϵ turbulence model. As upstream boundary condition for the spray simulation, drop-size distributions measured under cold-spray conditions were used with Sauter mean diameter (SMD) correlated according to Lefebvre. Calculations with different spray models were performed to study the effect of multicomponent vaporization, droplet-internal inhomogeneities, property-estimation methods, dispersion modeling, and swirl correction to the k-ϵ model. Considerable differences were found in fuel-vapor distribution when using different models. The LIF measurements and the numerical simulations were compared in terms of the fuel-vapor distribution. The simulation results were found to be very sensitive to the initial SMD, in particular in the presence of air swirl. Inaccuracies in the estimated SMD, therefore, constitute the primary accuracy limitation of the simulation. By adjusting the SMD, in many cases good agreement between measurement and simulation could be obtained. Remaining discrepancies that cannot be attributed to SMD adjustments are supposed to originate either from a turbulence-modeling error and the occurrence of secondary droplet breakup, which was not modeled, or, on the other hand, to the error by assuming a proportionality between LIF intensity and fuel oil concentration.

Development of a 1300.DEG.C.-Class Gas Turbine Combustor Burning Coal-Derived Low-BTU Gaseous Fuels. 4th Report. Experimental Evaluation of an Advanced Rich-Lean Combustor under High-Pressure Conditions.

Development of a 1300.DEG.C.-Class Gas Turbine Combustor Burning Coal-Derived Low-BTU Gaseous Fuels. 4th Report. Experimental Evaluation of an Advanced Rich-Lean Combustor under High-Pressure Conditions.

Development of a 1300.DEG.C.-class gas turbine combustor burning coal-derived low BTU gaseous fuels. 3rd Report, Experimental evaluation of an advanced rich-lean combustor.

This paper describes the development of a 1300°C class gas turbine combustor burning coal-derived low-Btu gaseous fuels. Coal-derived gaseous fuels contain NH3 if a gas cleaning system is hot type and NH3 will be converted to NOx in the gas turbine combustion process. Combustion tests were conducted by using the newly designed, advanced rich-lean combustor. Combustion stability was excellent for the testing combustor because of a subcombustor, so combustion stability could be obtained even when the calorific value of fuel decreased to about 2 600 KJ/m3N. As for NOx emission, NH3 conversion to NOx was 40% under the full load condition at 1300°C of the combustor exit gas temperature for 1000ppmv of NH3 concentration and 0.7vol% of CH4 in the fuel.

Development of a 1300.DEG.C.-class gas turbine combustor burning coal-derined low BTU gaseous fuels. 2nd Report, Low NOx combustion technology by rich-lean combustion.

This paper describes the low-fuel NOx combustion technology of a gas turbine combustor burning coal-derived low calorific value gaseous fuel. Combustion tests were conducted using the full-scale combustor of a 150MW-class gas turbine. Rich-lean combustion was very effective for decreasing fuel NOx emissions. However, in rich-lean combustion, the flame stability must be maintained with an increasing equivalence ratio in a primary combustion zone. The flame stability of the tested combustor which has a subcombustor was excellent, so the optimum equivalence ratio in a primary combustion zone can be made adjustable in the design of a low fuel NOx combustor.