Gas Turbine Combustion Chamber Research Articles

Performance Analysis of Small Size Compressed Air Energy Storage Systems for Power Augmentation: Air Injection and Air Injection/Expander Schemes

ABSTRACTTwo small size second-generation compressed air energy storage (CAES) systems have been investigated. Both plants are based on a 4600 kW Mercury recuperated gas turbine (GT) and on an artificial air storage system. In CAES air injection (CAES AI) plant, the stored compressed air is mixed with the air flow exiting the GT compressor and fed after a recuperative heating to the GT combustion chamber. A topping air expander is included in the CAES air injection/expander (CAES AI/E) plant scheme. Preliminary evaluations have been carried out to assess the maximum achievable GT power augmentation taking safety of operations and plant life duration into consideration. Plant performance has been evaluated during the overall operational cycle (charging, storage and discharging phases). CAES AI plant allows a 30% maximum extra power delivery (some 1500 kW) in respect to the nominal design GT power. The introduction of the topping air expander in CAES AI/E plant allows an additional power production of some 300 kW. Both plants have shown storage efficiency improvements by reducing the discharge period duration. Satisfactory values around 70% have been found in the best operating conditions.

A Weakly Nonlinear Approach Based on a Distributed Flame Describing Function to Study the Combustion Dynamics of a Full-Scale Lean-Premixed Swirled Burner

Modern combustion chambers of gas turbines for power generation and aero-engines suffer of thermo-acoustic combustion instabilities generated by the coupling of heat release rate fluctuations with pressure oscillations. The present article reports a numerical analysis of limit cycles arising in a longitudinal combustor. This corresponds to experiments carried out on the longitudinal rig for instability analysis (LRIA) test facility equipped with a full-scale lean-premixed burner. Heat release rate fluctuations are modeled considering a distributed flame describing function (DFDF), since the flame under analysis is not compact with respect to the wavelengths of the unstable modes recorded experimentally. For each point of the flame, a saturation model is assumed for the gain and the phase of the DFDF with increasing amplitude of velocity fluctuations. A weakly nonlinear stability analysis is performed by combining the DFDF with a Helmholtz solver to determine the limit cycle condition. The numerical approach is used to study two configurations of the rig characterized by different lengths of the combustion chamber. In each configuration, a good match has been found between numerical predictions and experiments in terms of frequency and wave shape of the unstable mode. Time-resolved pressure fluctuations in the system plenum and chamber are reconstructed and compared with measurements. A suitable estimate of the limit cycle oscillation is found.

An Experimental Apparatus and Procedure for the Simulation of Thermal Stresses in Gas Turbine Combustion Chamber Panels Made of Ceramic Matrix Composites

This paper presents an experimental procedure developed to simulate the behavior of ceramic matrix composites (CMCs) under the cyclic thermal stresses of a gas turbine combustion chamber. An experimental apparatus was assembled that produces a temperature gradient across the thickness of a CMC specimen while holding the specimen at its two extremities, which simulates the bending stress that would be observed at the center of a combustor panel. Preliminary validation tests were performed in which A-N720 oxide–oxide CMC specimens were heated to a surface temperature of up to 1160 °C using an infrared heater, which allowed for the calibration of heat losses and material thermal conductivity. The specimen test conditions were compared with predicted conditions in generic annular combustor panels made of the same material. Provided that a more powerful heat source is made available to reach sufficiently high temperatures and through-thickness temperature gradients simultaneously, the proposed experiment promises to allow laboratory observation of representative deterioration modes of a CMC inside an actual combustion chamber.

Flame volume prediction and validation for lean blow-out of gas turbine combustor

ABSTRACTLean Blow-Out (LBO) limits are critically important in the operation of aero engines. Previously, Lefebvre's LBO empirical correlation has been extended to the flame volume concept by the authors. Flame volume takes into account the effects of geometric configuration, spatial interaction of mixing jets, turbulence, heat transfer and combustion processes inside the gas turbine combustion chamber. For these reasons, LBO predictions based on flame volume are more accurate. Although LBO prediction accuracy has improved, it poses a challenge associated with Vfestimation in real gas turbine combustors. This work extends the approach of flame volume prediction based on fuel iterative approximation with cold flow simulations to reactive flow simulations. Flame volume for 11 combustor configurations were simulated and validated against experimental data. To make prediction methodology robust, as required in preliminary design stage, reactive flow simulations were carried out with the combination of presumed Probability Density Function (PDF) and discrete phase model (DPM) in Fluent 15.0 The criterion for flame identification was defined. Two important parameters—critical injection diameter (Dp,crit) and critical temperature (Tcrit)—were identified and their influence on reactive flow simulation was studied for Vfestimation. Results exhibit ±15% error in Vf estimation with experimental data.

Selection of technology for the low calorific synthetic gas combustion in the gas turbine combustion chamber

The leading gas turbines manufacturers are developing the technologies of the environmental friendly combustion of industrial and synthetic gases of low calorific values. In this case they are faced with critical problems concerning combustion stability assurance and the necessity of the gas turbines significant modernization due to the differences between the low calorific and natural gases. The numerical simulation results of the low calorific value synthetic gas combustion in the combustion chamber by means of different technologies are considered in the paper.

Numerical study of heat transfer enhancement due to the use of fractal-shaped design for impingement cooling

This paper describes a numerical analysis of a heat transfer enhancement technique that introduces fractal-shaped design for impingement cooling. Based on the gas turbine combustion chamber cooling, a fractal-shaped nozzle is designed for the constant flow area in a single impingement cooling model. The incompressible Reynolds-averaged Navier-Stokes equations are applied to the system using CFD software. The numerical results are compared with the experiment results for array impingement cooling.

Многофорсуночная камера сгорания – основа технологии обеспечения экологической безопасности авиационных газотурбинных двигателей

Многофорсуночная камера сгорания – основа технологии обеспечения экологической безопасности авиационных газотурбинных двигателей

Linearized Euler Equations for the Prediction of Linear High-Frequency Stability in Gas Turbine Combustors

A novel methodology for linear stability analysis of high-frequency thermoacoustic oscillations in gas turbine combustors is presented. The methodology is based on the linearized Euler equations (LEEs), which yield a high-fidelity description of acoustic wave propagation and damping in complex, nonuniform, reactive mean flow environments, such as encountered in gas turbine combustion chambers. Specifically, this work introduces three novelties to the community: (1) linear stability analysis on the basis of linearized Euler equations. (2) Explicit consideration of three-dimensional, acoustic oscillations at screech level frequencies, particularly the first-transversal mode. (3) Handling of noncompact flame coupling with LEE, that is, the spatially varying coupling dynamics between perturbation and unsteady flame response due to small acoustic wavelengths. Two different configurations of an experimental model combustor in terms of thermal power and mass flow rates are subject of the analysis. Linear flame driving is modeled by prescribing the unsteady heat release source term of the linearized Euler equations by local flame transfer functions, which are retrieved from first principles. The required steady-state flow field is numerically obtained via computational fluid dynamics (CFD), which is based on an extended flamelet-generated manifold (FGM) combustion model, taking into account heat transfer to the environment. The model is therefore highly suitable for such types of combustors. The configurations are simulated, and thermoacoustically characterized in terms of eigenfrequencies and growth rates associated with the first-transversal mode. The findings are validated against experimentally observed thermoacoustic stability characteristics. On the basis of the results, new insights into the acoustic field are discussed.

Weakly nonlinear analysis of thermoacoustic instabilities in annular combustors

Rotationally symmetric annular combustors are of practical importance because they generically resemble combustion chambers in gas turbines, in which thermoacoustically driven oscillations are a major concern. We focus on azimuthal thermoacoustic oscillations and model the fluctuating heat release rate as being dependent only on the local pressure in the combustion chamber. We study the dynamics of the annular combustor with a finite number of compact flames equispaced around the annulus, and characterize the flames’ response with a describing function. We discuss the existence, amplitude and the stability of standing and spinning waves, as a function of: (i) the number of the burners; (ii) the acoustic damping in the chamber; (iii) the flame response. We present the implications for industrial applications and the future direction of investigations. We then present as an example the first theoretical study of thermoacoustic triggering in annular combustors, which shows that rotationally symmetric annular chambers that are thermoacoustically unstable do not experience only stable spinning solutions, but can also experience stable standing solutions. We finally test the theory on one experiment with good agreement.

Numerical simulation of SGT-600 gas turbine combustor, flow characteristics analysis, and sensitivity measurement with respect to the main fuel holes diameter

In this article, the combustion chamber of SGT600 gas turbine with 18 Alstom EV burners is numerically simulated to investigate the flow field and combustion properties and analyze the sensitivity of this combustor to diameter of main fuel holes. The three-dimensional simulation is carried out based on the turbulent flame closure model for the two-equation turbulence model, k-ɛ, using OpenFOAM code for SGT600 industrial gas turbine burner. An accurate grid combined of structured and unstructured mesh scheme is employed, which is sufficiently fined in areas of high gradients. Grid independency is investigated and validation of the code established comparing the outlet temperature and flame shape with experimental results. Excellent agreement between numerical analyses and experimental data was observed, so that the difference between calculated and measured outlet temperature was 0.1%. On the basis of reasonable matching of the predicted and experimental results for the combustor, the computational fluid dynamics model enables the prediction of the heat shield and combustor’s wall temperature and critical points of operation. In this article, flow-field and operation condition of this combustor and sensitivity analysis with respect to the main fuel holes diameter are numerically investigated.

Parametric study of flow field and mixing characteristics of outwardly injected jets into a crossflow in a cylindrical chamber

Flow field and mixing characteristics of coolant radial jets injected radially from multiple nozzles rows of centreline distributer into a heated non-reacting crossflow in a cylindrical chamber is numerically investigated. The study simulates the process of air jets injection in the combustion chambers of gas turbines through discrete holes. Three-dimensional model using ANSYS-FLUENT 14.5 CFD package is used. The effects of jet-mixing ratio, nozzles diameter, distributer diameter, number of nozzles rows, number of nozzles per row on the penetration depth and mixing quality through chamber cross section are parametrically studied. The results are validated with the available experimental data and good agreement are obtained. The results showed that nozzle diameter, distributer diameter and jet-mixing ratio have effects on the penetration depth and the mixing quality compared to the effects of the number of nozzles per row and the number of nozzles rows. The effects are remarkable at high mixing ratio. The integral mixing quality along the chamber cross section increased with increasing mixing ratio, nozzles diameters, number of nozzles per row and number of nozzles rows. Dimensionless correlations for predicting the penetration depth and mixing quality in terms of the controlling parameters are developed.

Effect of geometrical contraction on vortex breakdown of swirling turbulent flow in a model combustor

Large Eddy Simulation (LES) studies of isothermal and incompressible turbulent swirling flows in a model gas turbine combustion chamber geometry have been carried out. The focus is on the effect of outlet geometry contraction on the vortex breakdown structure and the precessing vortex core in the chamber. Nine different outlet geometries with different contraction ratio Cr are considered. The results from a baseline case are compared with experimental data in the literature. The swirling flow is generated using a swirler with fifteen guide vanes similar to an existing industrial gas turbine burner. In all cases the swirler and the main chamber geometry are kept the same. The detailed swirler geometry is considered in the simulation using unstructured grids. Sensitivity tests on the influence of the grid resolution and the subgrid scale models are carried out. The mean flow field shows different vortex breakdown structures when the contraction ratio changes from 0.325 to 1.0. In particular, along the axis of the chamber the flow is shown to switch its direction when the contraction increases as a result of the change of the structure of the center recirculation zone. The underlying flow physics is analyzed by comparing the budget terms in the momentum equations, and by performing a global instability analysis.

Investigation of Flow Aerodynamics for Optimal Fuel Placement and Mixing in the Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustion Chamber

This paper is concerned with optimizing the fuel–air mixing processes that take place within the radial swirler slot of a dry low emission (DLE) combustion system. The aerodynamics of the flow within the slot is complex and this, together with the placement of the fuel holes with cross injection, controls the mixing of the fuel and air. Computational fluid dynamics (CFD) with the shear stress transport (SST) (k–ω) turbulence model was used for flow and mixing predictions within the radial swirler slot and for conducting a CFD-based design of experiments (DOE) optimization study, in which different parameters related to the fuel injection holes were varied. The optimization study was comprised of 25 orthogonal design configurations in the Taguchi L25 orthogonal array (OA). The test domain for the CFD, and its experimental validation, was a large-scale representation of a swirler slot from the Siemens proprietary DLE combustion system. The DOE study showed that the number of fuel holes, injection hole diameter, and interhole distance are the most influential parameters for determining optimal fuel mixing. Consequently, the optimized mixing configuration obtained from the above study was experimentally tested on an atmospheric test facility. The mixing patterns from experiments at various axial locations across the slot are in good agreement with the mixing predictions from the optimal CFD model. The optimized fuel injection design improved mixing compared with the baseline design by about 60%.

Reduced-Order Modeling of Aeroacoustic Systems for Stability Analyses of Thermoacoustically Noncompact Gas Turbine Combustors

A methodology is presented to model noncompact thermoacoustic phenomena using reduced-order models (ROMs) based on the linearized Navier–Stokes equations (LNSEs). The method is applicable to geometries with a complex flow field as in a gas turbine combustion chamber. The LNSEs, and thus the resulting ROM, include coupling effects between acoustics and mean fluid flow and are hence capable of describing propagation and (e.g., vortical) damping of the acoustic fluctuations within the considered volume. Such an ROM then constitutes the main building block for a novel thermoacoustic stability analysis method via a low-order hybrid approach. This method presents an expansion to state-of-the-art low-order stability tools and is conceptually based on three core features: First, the multidimensional and volumetric nature of the ROM establishes access to account spatial variability and noncompact effects on heat-release fluctuations. As a result, it is particularly useful for high-frequency phenomena such as screech. Second, the LNSE basis grants the ROM the capability to reconstruct complex acoustic performances physically accurate. Third, the formulation of the ROM in state-space allows convenient access to the frequency and time domain. In the time domain, nonlinear saturation mechanisms can be included, which reproduce the nonlinear stochastic limit cycle behavior of thermoacoustic oscillations. In order to demonstrate and verify the ROM's underlying methodology, a test case using an orifice-tube geometry as the acoustic volume is performed. The generation of the ROM of the orifice tube is conducted in a two-step procedure. As the first step, the geometrical domain is aeroacoustically characterized through the LNSE in frequency domain and discretized via the finite element method (FEM). The second step concerns the actual derivation of the ROM. The high-order dynamical system from the LNSE discretization is subjected to a modal reduction as order reduction technique. Mathematically, this modal reduction is the projection of the high-order (N∼ 200,000) system into its truncated left eigenspace. An order reduction of several magnitudes (ROM order: Nr∼ 100) is achieved. The resulting ROM contains all essential information about propagation and damping of the acoustic variables, and efficiently reproduces the aeroacoustic performance of the orifice tube. Validation is achieved by comparing ROM results against numerical and experimental benchmarks from LNSE–FEM simulations and test rig measurements, respectively. Excellent agreement is found, which grants the ROM modeling approach full eligibility for further usage in the context of thermoacoustic stability modeling. This work is concluded by a methodological demonstration of performing stability analyses of noncompact thermoacoustic systems using the herein presented ROMs.

Selecting the process arrangement for preparing the gas turbine working fluid for an integrated gasification combined-cycle power plant

Introduction of a combined-cycle technology based on fuel gasification integrated in the process cycle (commonly known as integrated gasification combined cycle technology) is among avenues of development activities aimed at achieving more efficient operation of coal-fired power units at thermal power plants. The introduction of this technology is presently facing the following difficulties: IGCC installations are characterized by high capital intensity, low energy efficiency, and insufficient reliability and availability indicators. It was revealed from an analysis of literature sources that these drawbacks are typical for the gas turbine working fluid preparation system, the main component of which is a gasification plant. Different methods for improving the gasification plant chemical efficiency were compared, including blast air high-temperature heating, use of industrial oxygen, and a combination of these two methods implying limited use of oxygen and moderate heating of blast air. Calculated investigations aimed at estimating the influence of methods for achieving more efficient air gasification are carried out taking as an example the gasifier produced by the Mitsubishi Heavy Industries (MHI) with a thermal capacity of 500 MW. The investigation procedure was verified against the known experimental data. Modes have been determined in which the use of high-temperature heating of blast air for gasification and cycle air upstream of the gas turbine combustion chamber makes it possible to increase the working fluid preparation system efficiency to a level exceeding the efficiency of the oxygen process performed according to the Shell technology. For the gasification plant’s configuration and the GTU working fluid preparation system be selected on a well-grounded basis, this work should be supplemented with technical-economic calculations.

Experimental and numerical investigations of the dry-low-NOx hydrogen micromix combustion chamber of an industrial gas turbine

Combined with the use of renewable energy sources for its production, hydrogen represents a possible alternative gas turbine fuel within future low emission power generation. Due to the large difference in the physical properties of hydrogen compared to other fuels such as natural gas, well established gas turbine combustion systems cannot be directly applied for dry-low-NOx (DLN) hydrogen combustion. Thus, the development of DLN combustion technologies is an essential and challenging task for the future of hydrogen fuelled gas turbines.The DLN micromix combustion principle for hydrogen fuel has been developed to significantly reduce NOx emissions. This combustion principle is based on cross-flow mixing of air and gaseous hydrogen which reacts in multiple miniaturized diffusion-type flames. The major advantages of this combustion principle are the inherent safety against flash-back and the low NOx emissions due to a very short residence time of reactants in the flame region of the micro-flames.The micromix combustion technology has been already proven experimentally and numerically for pure hydrogen fuel operation at different energy density levels. The aim of the present study is to apply and compare different combustion models for the characterization of the micromix flame structure, its interaction with the flow field and its NOx emissions.The study reveals great potential for the successful application of numerical flow simulation to predict flame structure and NOx emission level of micromix hydrogen combustion, help understanding the flow phenomena related with the micromixing, reaction zone and NOx formation and support further optimization of the burner performance.

Mechanical properties and mechanisms of hot forging processes of titanium alloy framed installation sides

Research of the titanium alloy installation sides used in combustion chambers of gas turbines resulted in the number of hot forging cycles being reduced, and the passing percentage of the produced installation sides was improved by using pneumatic forging equipment. The mechanical characteristics of the hot forging process were investigated, and mechanical equations were developed based on the thermo-force coupling principle and finite element method. The deformation process was simulated utilising computer-aided software, and based on the results, it was found that the parameters affecting the forming results included hammer speed, striking height and temperature. From this, a parameter variation range for reasonable strikes was proposed. A 3-month-long debugging process that involved more than 30 sets of experiments resulted in approximately 400 installation sides hot forged with a 100% product passing percentage. Moreover, the average number of strikes was reduced by 1·5 times.

Performance of a combined cooling heating and power system with mid-and-low temperature solar thermal energy and methanol decomposition integration

In this paper, a new distributed energy system that integrates the mid-and-low temperature solar energy thermochemical process and the methanol decomposition is proposed. Through the solar energy receiver/reactor, the energy collected by a parabolic trough concentrator, at 200–300°C, is used to drive the decomposition reaction of the methanol into the synthesis gas, and thus the solar thermal energy is converted to the chemical energy. The chemical energy of the synthesis gas released in the combustion chamber of a micro gas turbine is used to drive the combined cooling heating and power systems. Energy analysis and exergy analysis of the system are implemented to evaluate the feasibility of the proposed system. Under the considerations of the changes of the solar irradiation intensity, the off-design performances of the micro turbine and the variations of the load, the design and off-design thermodynamic performances of the system and the characteristics of the chemical energy storage are numerically studied. Numerical results indicate that the primary energy ratio of the system is 76.40%, and the net solar-electricity conversion rate reaches 22.56%, which is higher than exiting large-scale solar thermal power plants. Owing to the introduction of a the solar thermochemical energy storage in the proposed system, the power generation efficiency is insensitive to the variations of the solar radiation, and thus an efficient and stable utilization approach of the solar thermal energy is achieved at all work condition.

A numerical investigation of the entropy generation in and thermodynamic optimization of a combustion chamber

In this study, we are simulating the turbulent combustion of a mixed bluff-body swirl stabilized flame in a gas turbine combustion chamber and investigating the effects of different parameters, including the swirl number, distance between the air and fuel nozzle which is called bluff size, equivalence ratio, inlet fuel flow rate, and the inlet air velocity, on the entropy generation. We perform the process of the design of the combustion chamber by proposing the optimal value of each parameter based on the EGM (entropy generation minimization) method under the two maximum allowable temperature and size constraints. Two common methods of entropy generation calculation, one based on the overall entropy balance on a system and the other based on the local entropy generation rate calculation, are used and compared in this study. Our results show that the deviation between the total entropy generations calculated by the two methods is 6.4% in average which is an acceptable error in turbulent combustion simulations. Also, the two opposing factors, namely chemical reaction and heat transfer, have the main contribution to the total entropy generation.

Temperature Distribution on a Gas Turbine Shaft Exposed to Swirl Combustor Flue

A gas turbine shaft is generally exposed to high-temperature gases and may seriously be affected and overheated due to temperature fluctuations in the combustion chamber. Vortex flow in the combustion chamber may increase the heat release rate and combustion efficiency, as well as control the location of energy release. However, this may result in excessive temperature on the combustor equipment and gas turbine shaft. In this study, a new gas turbine combustion chamber implementing a liner around the shaft and the liquid-fuel feeding system is designed and fabricated. The influences of parameters such as the Reynolds number and the equivalence ratio are studied. Experimental results are compared with a numerical simulation using OpenFOAM, which is an open-source computational fluid dynamics software. The results show that the heat transfer to the liner at the head end of the combustion chamber is high enough; and at the outlet of the combustion chamber, it is relatively low. The effects of parameters such as the equivalence ratio and the mass flow rate of the oxidizer on the temperature of the liner without cooling are investigated and compared with the numerical solution. Also, in the numerical simulation, the swirl intensity along the chamber is provided. These types of combustion chambers can be used in gas turbine engines due to their low weight, short length, and better mixing.