Industrial Gas Turbine Combustor Research Articles

Investigation of swirl premixed dimethyl ether/methane flame stability and combustion characteristics in an industrial gas turbine combustor

In this paper, a new scheme for DME/methane (CH4) blended fuel combustion in an industrial gas turbine is proposed and numerical calculations are conducted to reveal the swirl premixed flame stability and combustion characteristics. The results show that injecting recirculated flue gas into the inlet gas restrains the flashback induced by high DME blending ratios and achieves the fully substitution of CH4 by DME. The DME/CH4 flame stability boundary is strongly correlaterd with the laminar flame speed and the adiabatic flame temperature. Therefore, it is recommended to set up the operating conditions of DME/CH4 industrial gas turbines by maintaining a fixed value of the laminar flame speed or adiabatic flame temperature to guarantee burner safety. Additionally, the combustion characteristics of DME/CH4 flames were evaluated under different operating conditions. The results indicate that the two uniformity factors PF and γT are largely independent of the DME blending ratio. As the equivalence ratio increases, PF shows a slight overall rise but remains below 1 %. NO and CO emissions are both directly proportional to the DME blending ratio and the equivalence ratio. Notably, as the flame transitions from a stable state to combustion-induced vortex breakdown flashback, the growth rates of NO and CO emissions rise sharply. In this case, NO emissions increase by 136 %, while CO emissions rise by 126 %.

Investigation of Viscor and Methanol Spray Dynamics using Proper Orthogonal Decomposition in Siemens Energy Industrial Atomisers

Abstract The demand to reduce carbon emissions has prompted research into alternative fuels that can replace conventional fuels like diesel in industrial gas turbines. Among different potential biofuels and e-fuels, methanol emerges as a sustainable and high-performance alternative to diesel for gas turbine applications. It is well established that the fuel physical properties, spray dynamics and degree of atomisation are strongly correlated and affect the engine performance. In this study, Proper Orthogonal Decomposition (POD) was applied on spatio-temporally resolved images to characterise Viscor, here used as diesel surrogate, and methanol sprays of pressure-swirl atomisers employed in Siemens Energy industrial gas turbine (SGT-400) combustors. The methanol experimental results were then compared against Viscor results at analogous operating conditions, including density adjusted atomiser pressure drop and ambient pressures. Results confirmed that the methanol spray cone angle is slightly wider than Viscor at corresponding operating conditions. The POD analysis allowed to identify dominant spatial oscillation modes and characterise them in terms of oscillation amplitude, wavelength and onset distance from the atomiser edge for both fuels. Oscillation wavelengths and maximum amplitudes were found to correlate with Weber number, average SMD and axial jet velocities.

An early detection indicator of combustion instability for an industrial gas turbine combustor

Detection of combustion instability is crucial for the safety and reliability of gas turbines. In this paper, the recurrence quantification analysis (RQA) and multi-fractal analysis (MFA) methods are applied to investigate the transition process from combustion noise to combustion instability in an industrial-scale combustor. Based on the dynamic pressure (DP) obtained from high pressure and high temperature tests, a novel method is proposed to construct early detection indicators (EDI) of combustion instability. The method is mainly based on the three-dimensional map of the recurrence rate, Hurst exponent, and root mean square ratio. A regression method and SVM are applied to define the classification boundary. For three test cases, the results showed that the proposed EDI can effectively detect the onset of combustion instability. Compared to the conventional method based on the root mean square levels of dynamic pressure, the EDI has capability to forecast the onset of combustion instability approximately a few hundred milliseconds in advance.

Longitudinal and azimuthal thermo-acoustic instabilities in an industrial gas turbine combustor operating at elevated pressure

This work numerically investigates longitudinal and azimuthal thermo-acoustic instabilities in the swirl-stabilised can-type industrial SGT-100 gas turbine combustor operated at elevated pressures of 3 and 6 bar. Previous experiments have shown that the combustor is susceptible to self-excited flame oscillations sustained by a thermo-acoustic feedback loop at specific operating conditions. In order to gain a better understanding of this feedback loop, a fully compressible large eddy simulation method is applied. The unknown sub-grid scale turbulence-chemistry interactions are modelled via a transported probability density function approach solved by the Eulerian stochastic fields method. First, the reaction zones and global flame topology at both operating pressures are analysed and compared to experimental images providing good qualitative agreement. Radial profiles of time-averaged and root-mean-square quantities furthermore demonstrate good quantitative agreement with the available measurement data. The applied simulation approach is capable of successfully reproducing self-excited thermo-acoustic instabilities in the longitudinal direction. The fundamental frequency of the predicted limit-cycle oscillation matches the experimentally measured frequency with high accuracy. Similar to the experimental observations, the fluctuation amplitudes of the pressure and global heat release rate increase significantly upon increasing the mean operating pressure from 3 to 6 bar. In addition to the dominant longitudinal mode, a high-frequency, low-amplitude azimuthal mode is also identified at both pressures. This azimuthal mode is periodically amplified and attenuated by the superposed longitudinal mode and induces small asymmetric (around the burner circumference) fluctuations of the local fuel and total mixture mass flow rates entering the flame region.

Multi-Objective Experimental Combustor Development Using Surrogate Model-Based Optimization

Abstract The majority of premixed industrial gas turbine combustion systems feature two or more separately controlled fuel lines. Every additional fuel line improves the operational flexibility but increases the complexity of the system. When designing such a system, the goals are low emissions of various pollutants and avoiding lean blowout or extinction. Typically, these limitations become critical under different load conditions of the machines. Therefore, it is particularly challenging to develop combustors for stable and clean combustion over a wide operating range. In this study, we apply the Gaussian process regression machine learning method for application to burner development, with the aim of improving the process, which is often driven by a trial-and-error approach. To do so, a special pilot unit is installed into a full-scale industrial swirl combustor. The pilot features 61 positions of fuel injection, each of which is equipped with an individual valve, allowing to modify the fuel–air mixture close to the flame root in various degrees. In fully automatized atmospheric tests, we use the pilot system to train two surrogate models for different design objectives of the combustor, relevant for full load and part load operation, respectively. Once trained, the models allow for prediction for any possible injection scheme. In combination, they can be used to identify pilot injector configurations with an improved operation range in terms of low NOx emissions and part load stability. The adopted multimodel approach enables combustor design specifically for high operational flexibility of gas turbines, but can also be extended to other similar industrial development processes.

Numerical investigation of hydrogen addition effects to a methane-fueled high-pressure combustion chamber

To get a general understanding of hydrogen fuel usage in a real-condition high-pressure industrial gas turbine burner operating at 15 atm pressure, the effects of hydrogen addition to methane fuel are studied numerically. Methane-hydrogen premixed fuel-lean flame is investigated while hydrogen is substituted for methane at a fixed fuel and air mass flow rate at the burner inlet. Steady-state reacting and swirling flow equations (RANS) are solved using the standard k−ε model as the turbulence model. A detailed methane combustion mechanism GRI 2.11 is used to simulate methane-hydrogen combustion with Finite Rate formulation more accurately. Temperature and axial velocity variation and important pollutant species emissions such as CO, CO2, and NOx were investigated at the combustion chamber exit. Flame shape, flow pattern, and flame location variation with hydrogen addition were studied due to hydrogen flashback limits. The hydrogen addition leads to higher temperatures inside the burner and the hot zone inside the combustion chamber extends and moves toward the fuel inlet. Flow structure including recirculation zones change with hydrogen addition. CO emission increases by hydrogen addition to the fuel mixture near the burner exit while CO2 mass fraction is reduced. A significant increase in NO mass fraction with hydrogen addition was observed near the burner exit due to higher temperature.

산업용 가스터빈 연소기에서 연소 모델에 따른 수소 화염의 역화 특성 비교연구

Four different combustion models were investigated to test hydrogen flame flashback prediction capability in an industrial gas turbine combustor. The applied combustion models are (i) flamelet generated manifold -finite rate (FGM-FR) model, (ii) flamelet generated manifold - turbulent flame speed (FGM-ST) model, (iii) steady diffusion flamelet (SDF) model, and (iv) eddy dissipation concept (EDC) model. Two conditions were simulated which showed experimentally non-flashback and flashback respectively. For the experimentally non-flashback condition, FGM-ST, SDF, and EDC model simulations show flashback, while FGM-FR did not show flashback. For the experimentally flashback condition, FGM-ST, SDF, and EDC model simulations show flashback, while FGM-FR did not show flashback. To be able to predict hydrogen-flame flashback, further investigation on combustion model are needed.

Investigation of Adaptive Mesh Refinement on an Industrial Gas Turbine Combustor

Abstract An adaptive mesh refinement (AMR) method is demonstrated for Large Eddy Simulations (LES) of an industrial gas turbine combustor, the SGT-100 provided by Siemens Energy Industrial Turbomachinery Ltd. In this paper, the simcenterstar-ccm+® solver is used to dynamically refine a series of Large Eddy Simulations with a Flamelet Generated Manifold (FGM) combustion model as applied to the SGT-100. Mesh refinement criteria are defined using second gradients of mixture fraction and reaction progress. Two meshes are assessed with and without AMR. The results are then compared to a refined static mesh and experimental data. The accuracy and computational cost of the static and adaptively refined meshes are discussed. It is shown that AMR can provide close to 2× speed up compared to a refined static mesh with similar predictions of mean and RMS quantities of the flow field, flame temperature and major species.

Numerically study of CH4/NH3 combustion characteristics in an industrial gas turbine combustor based on a reduced mechanism

This study numerically investigated ammonia/methane combustion characteristics (e.g. flame structure, temperature and species field) and velocity field in an industrial DLN gas turbine combustor with ammonia mass fraction up to 70%. To ensure accuracy and efficiency, a detailed mechanism based on GRI-Mech 3.0 and Otomo model was firstly assembled and then reduced via DRGEP and sensitive analysis. Both mechanisms show good performance for ignition delay and laminar flame speed calculation under gas turbine combustors’ working conditions. Numerical results of the combustor show that when fuel’s ammonia ratio is above 0.3, the flame is no longer “V-shaped”, increasing ammonia fraction in the fuel will lead to a longer, thicker, higher lifted flame. However, velocity field and combustion efficiency are not sensitive to fuel’s ammonia content. Combustion of ammonia/methane will not occur at ϕ < 0.5 in the combustor. Methane and ammonia consumption regions are at the same position, and NOx can form upstream of the flame front. With the increase of ammonia fraction in the fuel, an opposed effect was found for OH and HNO concentration, this leads NOx emissions to increase first and then decrease.

Investigation of flame evolution and stability characteristics of H2-enriched natural gas fuel in an industrial gas turbine combustor

Enhancing the H2 blending ratio in industrial gas turbines is essential to reduce fossil energy consumption and achieve carbon neutrality. However, several uncertainties still exist in their safe operation with H2 addition. In this work, a numerical investigation is conducted to evaluate the behavior and combustion stability of an H2-enriched natural gas fuel premixed swirl flame in an industrial gas turbine. The results indicate that the flame exhibits three types of behaviors upon increasing the H2 blending ratio, i.e., stable combustion, central flashback, and boundary layer flashback. The flame structure is highly sensitive to the inlet air temperature. The combustion reaction zone moves to the swirler as the inlet air temperature decreases, which in turn aggravates the central flashback. Injecting recirculated flue gas into the inlet air is proposed to restrain the central flashback. It is found that the flashback and blow-out limits exhibit quadratic polynomial and linear relationships with the recirculated flue gas ratio, respectively. The laminar flame speed of H2-enriched natural gas premixed flames with recirculated flue gas dilution at the flashback limit is 35.8 ± 0.5 cm/s. It is recommended to design or control H2-blended gas turbine burners with a laminar flame speed to ensure operational safety.

On the convective wave equation for the investigation of combustor stability using FEM-methods

Solving the Helmholtz equation with spatially resolved finite element method (FEM) approaches is a well-established and cost-efficient methodology to numerically predict thermoacoustic instabilities. With the implied zero Mach number assumption all interaction mechanisms between acoustics and the mean flow velocity including the advection of acoustic waves are neglected. Incorporating these mechanisms requires higher-order approaches that come at massively increased computational cost. A tradeoff might be the convective wave equation in frequency domain, which covers the advection of waves and comes at equivalent cost as the Helmholtz equation. However, with this equation only being valid for uniform mean flow velocities it is normally not applicable to combustion processes. The present paper strives for analyzing the introduced errors when applying the convective wave equation to thermoacoustic stability analyses. Therefore, an acoustically consistent, inhomogeneous convective wave equation is derived first. Similar to Lighthill’s analogy, terms describing the interaction between acoustics and non-uniform mean flows are considered as sources. For the use with FEM approaches, a complete framework of the equation in weak formulation is provided. This includes suitable impedance boundary conditions and a transfer matrix coupling procedure. In a modal stability analysis of an industrial gas turbine combustion chamber, the homogeneous wave equation in frequency domain is subsequently compared to the Helmholtz equation and the consistent Acoustic Perturbation Equations (APE). The impact of selected source terms on the solution is investigated. Finally, a methodology using the convective wave equation in frequency domain with vanishing source terms in arbitrary mean flow fields is presented.

Investigation on Flame Evolution and Stability Characteristics of H2-Enriched Natural Gas Fuel in an Industrial Gas Turbine Combustor

Investigation on Flame Evolution and Stability Characteristics of H2-Enriched Natural Gas Fuel in an Industrial Gas Turbine Combustor

Numerically Study of Ch4/Nh3 Combustion Characteristics in an Industrial Gas Turbine Combustor Based on a Reduced Mechanism

Numerically Study of Ch4/Nh3 Combustion Characteristics in an Industrial Gas Turbine Combustor Based on a Reduced Mechanism

CO Emission Modeling in a Heavy Duty Annular Combustor Operating With Natural Gas

Abstract This paper summarizes the development of a large-eddy simulation (LES)-based approach for the prediction of CO emission in an industrial gas turbine combustor. Since the operating point of the modern combustors is really close to the extinction limit, the availability of a tool able to detect the onset of high-CO production can be useful for the proper definition of the combustion chamber air split or to introduce design improvements for the premixer itself. The accurate prediction of CO cannot rely on the flamelet assumption, representing the fundament of the modern combustion models. Consequently, in this work, the extended turbulent flame speed closure (ETFSC) of the standard flamelet generated manifold (FGM) model is employed to consider the effect of the heat loss and the strain rate on the flame brush. Moreover, a customized CO-Damköhler number is introduced to decouple the in-flame CO production region from the postflame contribution where the oxidation takes place. A fully premixed burner working at representative values of pressure and flame temperature of an annular combustor is selected for the validation phase of the process. The comparison against the experimental data shows that the process is not only able to capture the trend but also to predict CO in a quantitative manner. In particular, the interaction between the flame and the air fluxes at some critical sections of the combustor, leading the CO emission from the equilibrium value to the super-equilibrium, has been correctly reproduced.

Numerical simulation of CO formation and reduction on flame propagation due to heat loss through the cooled wall

To realize further low carbon monoxide (CO) emissions for industrial gas turbine combustors, the elucidation of the CO formation and reduction mechanism for lean premixed combustion is crucial. In this study, one-dimensional numerical simulations using a detailed reaction mechanism approach and two-dimensional numerical simulations using a detailed reaction mechanism approach or a non-adiabatic flamelet generated manifolds (NA-FGM) approach are applied to CH4-air premixed flames near a cooled wall. The effects of the equivalence ratio (0.5, 0.7 and 1.0), pressure (0.1 and 2.0 MPa), and wall temperature (300 and 750 K) on the CO emissions is investigated. The results indicate that the influence of the wall temperature is the most significant on the CO reduction rate. For the lower wall temperature, the CO reduction rate in the vicinity of the cooled wall becomes lower, thereby has a risk to increase the CO emissions. At the pressure of 2.0 MPa and the equivalence ratio of 0.5, the CO reduction rate at a wall temperature of 300 K is only 16.8% of that at a wall temperature of 750 K. This suggests that the control of heat loss through the wall could be key to effectively reducing the CO emissions from combustors.

Hydrogen addition effect on NO formation in methane/air lean-premixed flames at elevated pressure

The present study investigates freely propagating methane/hydrogen lean-premixed laminar flames at elevated pressures to understand the hydrogen addition effect of natural gas on the NO formation under the conditions of industrial gas turbine combustors. The detailed chemical kinetic model which was used in the previous study on the NO formation in high pressure methane/air premixed flames was adopted for the present study to analyze NO formation of methane/hydrogen premixed flames. The present mechanism shows good agreement with experimental data for methane/hydrogen mixtures, including ignition delay times, laminar burning velocities, and NO concentration in premixed flames. Hydrogen addition to methane/air mixtures with maintaining methane content leads to the increase of NO concentration in laminar premixed flames due to the higher flame temperature. Methane/hydrogen/argon/air premixed flames are simulated to avoid the flame temperature effect on NO formation over a pressure range of 1–20atm and equivalence ratio of 0.55. Kinetic analyses shows that the N2O mechanism is important on NO formation for lean flames between the reaction zone and postflame region, and thermal NO is dominant in the postflame zone. The hydrogen addition leads to the increase of NO formation from prompt NO and NNH mechanisms, while NO formation from thermal and N2O mechanisms are decreased. Additionally, the NO formation in the postflame zone has positive pressure dependencies for thermal NO with an exponent of 0.5. Sensitivity analysis results identify that the initiation reaction step for the thermal NO and the N2O mechanism related reactions are sensitive to NO formation near the reaction zone.

Heat transfer characteristics of triple-stage impingement designs and their application for industrial gas turbine combustor liner cooling

This paper reports a triple-stage impingement concept with two optimized designs to tackle the common design challenges of the adverse effect of cross flow and coolant maldistribution on impingement cooling for modern gas turbine components. Flow structure and heat transfer characteristics were investigated at two different constant uniform wall temperatures with lower wall temperature related to lower wall to jet temperature ratio and the higher wall temperature related to higher wall to jet temperature ratio. The feasibility of application the triple-stage impingement cooling designs to a gas turbine combustor liner was conducted through Conjugate Heat Transfer analysis by applying a wall with realistic material thermal properties at two different constant wall heat fluxes. All studies were carried out at engine operation conditions with high air pressure and temperature. The results show that the triple-stage impingement cooling designs can reinitiate impingement jets at each stage, which greatly reduces the cross flow impact and local thermal gradient. The staging of cooling air for combustor cooling also offers better utilization of the cooling capacity. Even with 50% reduction in the cooling air consumption compared to conventional single-stage impingement design, both triple-stage impingement designs can still sufficiently cool the combustor liner. Both triple-stage impingement designs can be practically applied to gas turbine combustor liner cooling.

Lean blow-out prediction in an industrial gas turbine combustor through a LES-based CFD analysis

The use of lean premixed flames to control combustion temperature and limit nitric oxides (NOx) formation is a common practice in all the applications of land-based gas turbines irrespective of their size and power production capacity. Despite the capability of lean premixed combustion to nominally reduce NOx emissions well below the most strict international regulations, such technology still requires improvements to overcome the impact on whole engine operability due to possible onset of combustion instabilities and flame lean blow-out (LBO). Both phenomena involve highly unsteady processes resulting in challenging numerical modeling. Particularly critical is the prediction of lean blow-out mechanisms where the role of finite rate chemistry and turbulence cannot be easily simplified. The current study aims at proving the capability of a CFD methodology based on Large Eddy Simulation (LES) and on an extended version of the Turbulent Flame Closure (TFC), to describe and properly catching the dynamics of flame extinction at the leanest operating conditions in typical turbulent lean premixed flames adopted in gas turbine combustors. The methodology is first validated on a laboratory test case where detailed experimental results are available. The extended TFC model well describes the LBO process observed in an atmospheric swirl stabilized burner investigated at the University of Cambridge. The proposed approach is then applied to the investigation of a real scale combustor operated with a swirl lean burner, representing the standard device adopted by Baker-Hughes on the heavy-duty 16 MW class engine Nova LT16. An accelerated numerical procedure is used to trigger the LBO, considering both constant firing temperature and constant pilot split conditions. An excellent agreement is observed with respect to the data obtained on a full-annular test rig, confirming the validity of the developed LBO modeling strategy which can be used in design phase to improve the overall engine operability.

A Comparative Study of Natural Gas and Biogas Combustion in A Swirling Flow Gas Turbine Combustor

ABSTRACT In this study, non-premixed combustion of a traditional fuel-natural gas, and an alternative fuel-biogas, is simulated in a swirling flow industrial gas turbine combustor geometry which includes the combustor liner and the outside casing in order to replicate the flow and combustion in a real gas turbine combustor. The 3D combustion simulations are validated and the results for combustion of both gases are analyzed to compare and evaluate the viability of biogas as an alternative fuel for use in industrial gas turbine combustors. The combustion performance is evaluated based on multiple combustion performance optimization parameters, namely, the combustion efficiency, pattern factor, and pollutant emissions (CO and NO). The effects of two design parameters: swirl number and fuel injector diameter on the combustion performance optimization parameters are examined. The results have been analyzed to identify the best case for each combustion performance optimization parameter and a suitable trade-off case for both gases is proposed. Additionally, the comparison of the combustion performances of both gases revealed that despite possessing much lower methane and hence lower heating value (LHV), a combination of swirl number and fuel injector diameter for biogas of a specific composition results in a combustion performance comparable to natural gas along with lower NO emission, although at the expense of higher CO emission. Therefore, biogas can potentially be utilized as an alternative fuel in industrial gas turbine combustors, and methods for reducing CO emission can be devised.

Fault Detection in Fuel Distribution Characteristics of Industrial Gas Turbine Combustor Using Artificial Neural Network Method

Fault Detection in Fuel Distribution Characteristics of Industrial Gas Turbine Combustor Using Artificial Neural Network Method