Gas Turbine Combustion Systems Research Articles

Non-reacting Flow Analysis from Combustor Inlet to Outlet using Computational Fluid Dynamics Code

This paper describes non-reacting flow analysis of a gas turbine combustion system. The method is based on the solution of Navier-Strokes equations using generalised non-orthogonal coordinate system. The turbulence effects are modelled through the renormalisation group k-E model. The method has been applied to a practical gas turbine combustor. The combustion system includes swirler vane passages, fuel nozzles, rotor bleed, customer bleed, air-blast atomiser, swirl cone, and all holes in primary , dilution , dome, flare, and cooling ring. The total geometry has been created using the pre-processors GAMBIT and CATIA, and the meshing has been done using GAMBIT, and the analysis carried out in a FLUENT solver. The interaction between the diffuser and the combustor external flows plays a key role in controlling the pressure loss, air flow distribution around the combustor liner, durability, and stability. The aero gas turbine combustor designs are generally guided by experimental methods and past experience; however, experimental methods are inherently slow, costly, especially at high temperature engine-operating conditions. These drawbacks and the growing need to understand the complex flow-field phenomenon involved, have led to the development of a numerical model for predicting flow in the gas turbine combustor. These models are used to optimise the design of the combustor and its subcomponents, and reduce cost, time, and the number of experiments.

A MODEL FOR THE THERMOACOUSTIC RESPONSE OF A PREMIXED SWIRL BURNER, PART I: ACOUSTIC ASPECTS

Results from previous measurements on a small laboratory swirl burner undergoing self-excited acoustic oscillations with premixtures of either CH4 or C3H8 are summarized. The measurements of acoustic pressure and the distribution of chemiluminescent emission were used to deduce semi-empirical descriptions of the flame response functions, and these are used here in conjunction with a validated model for the acoustics of the premixture supply system, burner, and combustion chamber to reproduce the excitation frequencies and to deduce the required amplitudes of the flame response function. Variations of the burner flow rate and the equivalence ratio are examined, as is the sensitivity of the results to the acoustic and flame parameters. The results are of considerable relevance to the response of industrial gas-turbine combustion systems, and the calculations lay the foundations for the fundamental model of the flame response that is derived in Part II.

Pre-integrated Nonequilibrium Combustion-Response Mapping for Gas Turbine Emissions

In gas turbine combustion the gas dynamic and chemical energy release mechanisms have comparable time scales, so that equilibrium chemistry is inadequate for predicting species formation (emissions). In current practice either equilibrium chemical reactions are coupled with experimentally derived empirical equations, or time-consuming computations are used. Coupling nonequilibrium chemistry, fluid dynamic, and initial and boundary condition equations results in large sets of numerically stiff equations; and their time integration demands enormous computational resources. The response modeling approach has been used successfully for large reaction sets. This paper makes two new contributions. First it shows how pre-integration of the heat release maps eliminates the stiffness of the equations. This is a new modification to the response mapping approach, and it performs satisfactorily for non-diffusion systems. Second the theoretical framework is further extended to predict species formation in cases with diffusion, which is applicable to gas turbine combustion systems and others. The methodology to implement this approach to reacting systems, and to gas turbine combustion, is presented. The benefits over other reaction-mapping techniques are discussed.

Unsteadiness of the Port Feed and Jet Flows Within a Gas Turbine Combustion System

This paper describes an experimental investigation on a gas turbine combustor geometry that is typical of current aerospace applications. The isothermal investigation has concentrated on the flow approaching and passing through a primary port, and the subsequent jet formed by this flow within the flame tube. It is widely accepted that the jet formed by a port in such a geometry is influenced by the mean approach flow conditions. This paper, though, addresses whether the high levels of turbulence and unsteadiness, as is typically found within the approach flow of these systems, can also affect the time dependent jet and flow field generated by the port. Measurements using both hot wire anemometry (HWA) and a three component Laser Doppler Anemometry (LDA) system were therefore used to characterize the flow field. Cross correlation of simultaneous measurements indicated that velocity fluctuations in the feed annulus correlate with fluctuations inside the port and flame tube. The sign and magnitude of the correlations are presented between various feed annulus, port and flame tube spatial locations. The results suggest the time dependent external flow field can influence the flow field within the flame tube and hence, potentially, flame stability, mixing and emissions.

Large eddy simulation of combustion processes under gas turbine conditions

The method of large eddy simulation (LES) has a high potential to accurately predict complex turbulent flows. Gas turbine combustion systems feature a number of phenomena interacting with each other such as swirl with recirculation, complex turbulent mixing and combustion of premixed, non-premixed as well as partially premixed nature. We therefore tend to approach the simulation of real gas turbine combustors step by step. The aim of this paper is to document some of the progress made at EKT in assessing the capability of LES in flows separately exhibiting distinct features of gas turbine combustors. Some results from two configurations are presented and discussed: a non-confined isothermal swirl flow with precessing vortex core and a non-premixed bluff-body flame.

New combustion systems for gas turbines (NGT)

Within the framework of an EC funded project the FLOX ® 1 Registered trade mark WS Wärmeprozesstechnik GmbH. 1 and COSTAIR burner technology will be investigated under gas turbine conditions. The major innovation of the project will be to show that the FLOX ® and COSTAIR burner technology is applicable to gas turbine conditions, e.g. high pressure and overall lean conditions in conjunction with improved operational performance compared to lean premixed combustion. Both systems are based on the principle of diffusion combustion. The new combustion systems will be designed for micro turbines and for large scale industrial turbines. The paper gives an overview about the project and the ongoing activities. First very promising results achieved under atmospheric test conditions will be presented.

Experimental Diagnostics for the Study of Combustion Instabilities in Lean Premixed Combustors

An improved understanding of the mechanisms of unstable combustion in lean premixed combustors is essential to the development of stable gas turbine combustion systems. To obtain such understanding, detailed experimental studies of the phenomenology of unstable combustion are required. A number of experimental diagnostic techniques for characterizing unstable combustion and the underlying instability mechanisms are discussed. This includes techniques based on pressure, chemiluminescence emission, infrared absorption, and laser-induced fluorescence measurements. The techniques themselves are discussed briefly; however, the primary objective is to present and discuss results illustrating how these techniques can be used to characterize the mechanisms of unstable combustion, to gain an improved understanding of unstable combustion, and to develop strategies for suppressing unstable combustion in lean premixed gas turbine combustors.

Prediction and Measurement of Thermoacoustic Improvements in Gas Turbines With Annular Combustion Systems

Environmental compatibility requires low emission burners for gas turbine power plants. In the past, significant progress has been made developing low NOx and CO burners by introducing lean premixed techniques in combination with annular combustion chambers. Unfortunately, these burners often have a more pronounced tendency to produce combustion-driven oscillations than conventional burner designs. The oscillations may be excited to such an extent that the risk of engine failure occurs. For this reason, the prediction of these thermoacoustic instabilities in the design phase of an engine becomes more and more important. A method based on linear acoustic four-pole elements has been developed to predict instabilities of the ring combustor of the 3A-series gas turbines. The complex network includes the whole combustion system starting from both compressor outlet and fuel supply system and ending at the turbine inlet. The flame frequency response was determined by a transient numerical simulation (step-function approach). Based on this method, possible improvements for the gas turbine are evaluated in this paper. First, the burner impedance is predicted theoretically and compared with results from measurements on a test rig for validation of the prediction approach. Next, the burner impedance in a gas turbine combustion system is analyzed and improved thermoacoustically. Stability analyses for the gas turbine combustion system show the positive impact of this improvement. Second, the interaction of the acoustic parts of the gas turbine system has been detuned systematically in circumferential direction of the annular combustion chamber in order to find a more stable configuration. Stability analyses show the positive effect of this measure as well. The results predicted are compared with measurements from engine operation. The comparisons of prediction and measurements show the applicability of the prediction method in order to evaluate the thermoacoustic stability of the combustor as well as to define possible countermeasures.

Acoustic Resonances of an Industrial Gas Turbine Combustion System

A theory is developed to describe low-frequency acoustic waves in the complicated diffuser/combustor geometry of a typical industrial gas turbine. This is applied to the RB211-DLE geometry to give predictions for the frequencies of the acoustic resonances at a range of operating conditions. The main resonant frequencies are to be found around 605 Hz (associated with the plenum) and around 461 Hz and 823 Hz (associated with the combustion chamber), as well as one at around 22 Hz (a bulk mode associated with the system as a whole). The stabilizing effects of a Helmholtz resonator, which models damping through nonlinear effects, are included, together with effects of coupled pressure waves in the fuel supply system.

Catalytic combustion for the production of energy

In this paper, attention is focused on adiabatic lean-premixed catalytic combustion, which has attracted interest in the last decades as an environmentally friendly and cost-effective alternative to flame combustion for power generation by gas turbines. The different configurations of the combustion systems for gas turbines are presented. and the results of pilot tests, full-scale bench tests and field trials with retrofitted machines are illustrated. The relevant physico-chemical and catalytic properties of highly active supported PdO catalysts, including reversible PdO–Pd transformation and low-temperature activity, are then addressed. The structural and catalytic properties of highly stable metal substituted hexaaluminates are also discussed. The use of fuel alternative to natural gas is briefly covered. The relevant features of mathematical models for both, the catalyst section and the homogeneous section, that can be used in the design and analysis of the catalytic combustor, are described and the major conclusions of the modelling activity are outlined. Finally, the research opportunities in the area are discussed.

99/02509 Evaluation of NO x production from black liquor gasification—gas turbine combustion systems

99/02509 Evaluation of NO x production from black liquor gasification—gas turbine combustion systems

Structural Integrity of a Gas Turbine Combustion System Subjected to Increased Dynamic Pressure

The effect of combustion dynamic pressure oscillations on the structural integrity of the MS 7001F dry low NOx2 (DLN 2) combustion system has been evaluated using ANSYS [1] finite element analyses and high cycle fatigue material data. Analytical results were validated with laboratory measurements on the combustion system subjected to combustion dynamic pressure at actual gas turbine temperature and pressure operating conditions. The combustion liner, transition piece, impingement sleeve, and supports were proven to have excellent durability when subjected to dynamic loads. No risk of structural failure exists at anticipated dynamic pressures using assumptions shown to be conservative.

Catalytic combustion for industrial gas turbines

This brief review provides a general account of work directed at the use of catalytic combustion in gas turbine engines. A major potential advantage of using catalytic combustion is that the fuel can be burnt efficiently at temperatures low enough (< 1500°C) to avoid significant oxidation of atmospheric nitrogen. This advantage was less important when catalytic combustion was demonstrated in the 1970s than it is today and received relatively little attention until the following decade. After discussion of the principles involved in the design of a combustor that must meet the mixing, size, performance and durability goals of a based gas turbine application, the review turns to accounts of experiments conducted on a laboratory scale with simple configurations. These established basic operating parameters for satisfactory combustion performance and led to larger scale work and to prototype design concepts for industrial gas turbines in the late 70s and early 80s. Test results were encouraging but were not pursued definitively in the U.S.A. Activity continued at several centres in Japan, with exploration of a number of different catalyst arrangements, geometries, and control systems, again with encouraging results. At the same time, there has been renewed interests in the U.S.A. and in Europe, spurred largely by the emphasis on reducing emissions of nitrogen oxides (NOx). The paper concludes with suggestions for further development of catalytically stabilized combustion systems for gas turbines. These systems must ensure adequate pre-catalyst temperature, with evenly premixed fuel and air, and sufficient temperature rise across the catalyst to ensure effective completion of reaction in a homogeneous reaction mode. The outstanding problems are largely concerned with questions of catalyst integrity and longevity in practical configurations and realistic engine operating conditions.

Perturbation analysis of a catalytic combustor

Lean premixed combustion (LPC) of natural gas is widely employed in stationary gas-turbine combustion systems to minimize pollutants formed at high temperature, such as nitrogen oxides, but can lead to secondary problems such as CO/UHC emissions at part load, lean flame blowout, and strong pressure oscillations approaching limit cycles. Catalytic combustion is an attractive option to LPC. A range of pressures from one to above ten atmospheres has been investigated, with inlet temperatures and velocities appropriate for operation under gas-turbine conditions. Temperature profiles have been obtained from images provided by an infrared camera mounted in the postflame gas, looking forward at the exit face of the catalyst. Dark relatively low temperature regions, analogous to sunspots, are sometimes apparent on the exit face. The temperature variation appears to be spatially periodic with a fairly small amplitude, on the order of less than 100 K. As long as the entrance conditions are held constant, these dark spots have been observed to survive for periods of time (minutes to tens of minutes) which are much longer than the fluid mechanical or chemical time scales in the flow. The present linear analysis yields conditions under which periodic temperature fields are possible. A nonlinear analysismore » becomes necessary if the amplitude becomes too large; however, the latter regime is not of operational interest since it corresponds to flame extinction on a large scale.« less

High-Intensity Burners with Low Nox Emissions

Experimental combustion and NOx emissions results are summarized for a range of jet shear layer combustion systems that have rapid fuel and air mixing, short intense flames, a high turn-down ratio and low NOx characteristics. Two burner sizes of 76 and 140 mm are investigated for propane and natural gas. Three jet shear layer burners are compared with axial and radial swirlers. The combustion techniques were developed for application to low NOx combustion systems for industrial gas turbines, where NOx emissions as low as 10 ppm at 15 per cent oxygen have been demonstrated. It is shown that at one bar pressure, gas turbine combustors and high-intensity burners operate at similar air flow, blockage and pressure loss conditions.

A Computational Procedure for Diffuser-Combustor Flow Interaction Analysis

This paper describes a diffuser-combustor flow interaction analysis procedure for gas turbine combustion systems. The method is based on the solution of the Navier–Stokes equations in a generalized nonorthogonal coordinate system. The turbulence effects are modeled via the standard two-equation (k-ε) model. The method has been applied to a practical gas turbine combustor-diffuser system that includes support struts and fuel nozzles. Results have been presented for a three-dimensional simulation, as well as for a simplified axisymmetric simulation. The flow exhibits significant three-dimensional behavior. The axisymmetric simulation is shown to predict the static pressure recovery and the total pressure losses reasonably well.

Three-dimensional analysis of gas turbine combustors

To achieve the required performance goals and structural durability of gas turbine combustion systems, a design approach was formulated to guide the development effort of the combustor. The approach combines the capabilities of the analytical tools with well-established empirical correlations. By this means, the impact of systematic modification to the details of the burner is easily determined. The validation effort of the developed model included the utilization of the data obtained for a number of production combustors that significantly varied in design and concept. Fuels used in these combustors included typical aviation fuels such as JP-4 and DF-2 as well as specially prepared high-density fuels. Model validation also involved the application of the model in the development phases of an annular combustor. Several modifications to the dome and primary zone features were proposed in this effort. The predictions of the combustor performance and wall temperatures made using the present approach were found to be in good agreement with the measurements.

Flow in Liner Holes for Countercurrent Combustion Systems

Heavy-duty gas turbine combustion systems have a “reverse flow” combustion-cooling air network. High-temperature gradients have been observed in some combustion liners around the plain holes, or around the cylindrical inserts welded into the mixing holes. Flow visualization tests were performed in a countercurrent flow facility. Measurements of pressure and velocity distributions in and around the mixing hole jet were taken, and mass flow rates and discharge coefficients were calculated in order to characterize and compare the two geometries. The results with a plain hole (square-edged orifice) and the cylindrical insert show the presence of a sharp separation region at the trailing edge (combustion side) of the liner hole, which may cause the high-temperature gradients observed under operating conditions. The measured discharge coefficients show a dependence on the insert geometry, the flow parameter (K), and the bottom section (combustion side) countercurrent flow velocity.

Full-Engine Field Test: An Approach to Improve the Gas Turbine Combustion System

For purposes of both final verification and optimization of TG 20 and TG 50 combustion systems, test programs have been carried out directly on full engines operating in the field, as well as in the test bench. These programs were carried out in two separate phases: the first one directed to determine the behavior at load by means of experimental data acquisition, including temperature distribution on the combustor exit plane for different burner arrangements, and the second one directed to optimize the ignition process and the acceleration sequence. This paper, after a brief description of the instrumentation used for each test, reports the most significant results burning both fuel oil and natural gas. Moreover, some peculiar operational problems are mentioned, along with their diagnosis and the corrections applied to the combustion system to solve them.

Measurement of velocity and kinetic energy of turbulence in swirling flows and their numerical prediction

AbstractSwirling flows are often employed in gas turbine combustion systems and high intensity industrial furnaces. A detailed analysis of the turbulence in the flow is necessary to achieve optimum combustion conditions. In this paper a method has been described to measure the turbulence levels in three directions using a hot wire anemometer. So far there is no established method available for measurement of turbulence in swirling and recirculating flows.The present method, it is hoped, will bridge the gap. The merit of the present method is the use of a single‐wire probe rather than the X‐probe. The method has been used for the measurement of turbulence levels in swirling recirculating flows generated by vane swirlers. From the measured turbulence levels, the kinetic energy of turbulence has been calculated and the results are compared with a well‐established numerical prediction method.Mean velocity measurements have also been made using a 3‐hole Pitot probe. The agreement between the measured and predicted values is quite satisfactory.