bluuebunny/crossref_metadata_2025 huggingface dataset:
Flame Stabilization by Hot Products Gases Recirculation in a Trapped Vortex Combustor
Authors: Burguburu Joseph , Cabot Gilles , Renou Bruno , Boukhalfa Abdelkrim Mourad , Cazalens Michel
Published: July 2013

New regulations regarding NOx emissions are forcing manufacturers to develop advanced research and technology strategies. Ultra-lean combustion is considered as an attractive solution; however, it generally produces combustion instabilities in swirl-stabilized burners. This work provides experimental results for a new burner technology based on two concepts: the trapped vortex combustor (TVC) and the ultra-compact combustor (UCC). Methane/air flame stabilization was achieved by generating hot product recirculation, with a rich pilot flame located in an annular cavity, and by flame holders located in the main flow slightly upstream of the cavity. In addition, azimuthal gyration could be added to the main flow to reproduce the suppression of the last diffuser stage, which increased the velocity and modified the mixing between the cavity and the mainstream due to centrifugal forces. The combustor characterization was performed by coupling several optical diagnostics, pollutant emissions, and pressure measurements (for both cold and reactive conditions) at atmospheric pressure. An understanding of the combustion dynamics was achieved through phase averaged PIV/CH* images. The analysis highlighted the importance of the stabilization process of a double vortex structure inside the cavity and the presence of reactive gas close to the upstream cavity wall. These conditions were improved by a high cavity equivalence ratio and a high main airflow rate. The addition of swirl considerably increased the flame stability.
Detailed Research on Rich-Lean Type Single Sector Combustor for Small Aircraft Engine Tested Under Practical Conditions Up to 3MPa
Authors: Makida Mitsumasa , Yamada Hideshi , Shimodaira Kazuo
Published: July 2013

In the TechCLEAN project of JAXA, experimental research has been conducted to develop a combustor for a small aircraft engine. The combustor was tuned to show the behavior of the Rich-Lean combustion through tests under atmospheric and practical conditions. Finally, through full annular combustion experiments under practical conditions, the combustor was tuned to reduce NOx emissions to almost 40% of the ICAO CAEP4 standard, also sustaining low CO and THC emissions. To investigate the performance of the combustor in detail, parametric experiments were conducted with single-sector combustors under additional test conditions in addition to design conditions of the target engine. Also the performance as a combustor for higher-efficient aircraft engine is examined by increasing inlet air pressure and temperature up to 3MPa and 825K in combustion tests. Obtained results of emission characteristics are discussed in this report.
Application of Scalar Dissipation Rate Model to Siemens DLE Combustors
Authors: Sadasivuni Suresh Kumar , Bulat Ghenadie , Sanderson Victoria , Swaminathan Nedunchezhian
Published: July 2013

The standard design process for the Siemens Industrial Turbomachinery, Lincoln, Dry Low Emissions combustion systems has adopted the Eddy Dissipation Model with Finite Rate Chemistry for reacting computational fluid dynamics simulations. The major drawbacks of this model have been the over-prediction of temperature and lack of species data limiting the applicability of the model.

A novel combustion model referred to as the Scalar Dissipation Rate Model has been developed recently based on a flamelet type assumption. Previous attempts to adopt the flamelet philosophy with alternative closure models have failed, with the prediction of unphysical phenomenon. The Scalar Dissipation Rate Model (SDRM) was developed from a physical understanding of scalar dissipation rate, signifying the rate of mixing of hot and cold fluids at scales relevant to sustain combustion, in flames and was validated using direct numerical simulations data and experimental measurements.

This paper reports on the first industrial application of the SDRM to SITL DLE combustion system. Previous applications have considered ideally premixed laboratory scale flames. The industrial application differs significantly in the complexity of the geometry, unmixedness and operating pressures. The model was implemented into ANSYS-CFX using their inbuilt command language. Simulations were run transiently using Scale Adaptive Simulation turbulence model, which switches between Large Eddy Simulation and Unsteady Reynolds Averaged Navier Stokes using a blending function.

The model was validated in a research SITL DLE combustion system prior to being applied to the actual industrial geometry at real operating conditions. This system consists of the SGT-100 burner with a glass square-sectioned combustor allowing for detailed diagnostics. This paper shows the successful validation of the SDRM against time averaged temperature and velocity within measurement errors.

The successful validation allowed application of the SDRM to the SGT-100 twin shaft at the relevant full load conditions. Limited validation data was available due to the complexity of measurement in the real geometry. Comparison of surface temperatures and combustor exit temperature profiles showed an improvement compared to EDM/FRC model. Furthermore, no unphysical phenomena were predicted.

This paper presents the successful application of the SDRM to the industrial combustion system. The model shows a marked improvement in the prediction of temperature over the EDM/FRC model previously used. This is of significant importance in the future applications of combustion CFD for understanding of hardware mechanical integrity, combustion emissions and dynamics of the flame.
Modeling Spray Formation in Gas Turbines: A New Meshless Approach
Authors: Hoefler C. , Braun S. , Koch R. , Bauer H.-J.
Published: July 2013

A new meshless Lagrangian particle code has been developed in order to tackle the challenging numerical modeling of primary atomization. In doing so the correct treatment and representation of the interfacial physics are crucial prerequisites. Grid based codes using interface tracking or interface capturing techniques, such as the Volume of Fluid or Level Set method, exhibit some difficulties regarding mass conservation, curvature capturing and interface diffusion. The objective of this work is to overcome these shortcomings of common state-of-the-art grid based FVM approaches. Our multi-dimensional meshless particle code is based on the Smoothed Particle Hydrodynamics method [1] [2]. Various test cases have been conducted, by which the capability of accurately capturing the physics of single and multiphase flows is verified and the future potential of this approach is demonstrated. Compressible as well as incompresssible fluids can be modeled. Surface tension effects are taken into account by two different models, one of them being more suitable for free surface flows and the other for simulating multiphase flows. Solid walls as well as periodic boundary conditions offer a broad variety of numerically modeling technical applications. In a first step, single phase calculations of shear driven liquid flows have been carried out. Furthermore, the disintegration of a gravity driven liquid jet emerging from a generic nozzle has been investigated in free surface simulations. The typical formation of a meniscus due to surface tension is observed. Spray formation is qualitatively in good agreement compared to experiments. Surface tension effects have been taken into account via the cohesive force model. Finally, the results of a two-phase simulation with a fluid density ratio of 1000, which is similar to a fuel-air fluid system as in airblast atomizers, are presented. The surface minimization and pressure jump across the droplet interface due to surface tension can be predicted accurately. The test cases conducted so far demonstrate the accuracy of the existing code and underline the promising potential of this new method for successfully predicting primary atomization.
Axial Swirler Outlet Shroud Influence on Premixed Combustion NOx Emissions for All the Combustion Airflow Passing Through the Swirler
Authors: Andrews Gordon E. , Ahmad Nasser T.
Published: July 2013

A 76mm diameter combustor with single axial flat 8 bladed swirlers of 30°, 45° and 60° vane angle were investigated at a reference Mach number of 0.05 or combustion intensity of 20MW/(m2bar), which represents all the combustion air passing through the swirler. The influence of a swirler outlet shroud or outlet orifice plate was investigated. This increased the pressure loss and the outer dump expansion recirculation zone size, D/d, and these were the main influences on the combustion performance. The swirlers were very large relative to the combustor so that they had a high air flow capacity. They had the same outer diameter, d, of 70mm with a cylindrical combustor diameter, D, of 76mm, D/d = 1.1. These swirlers had a decreasing hub size as the vane angle was increased. There was no significant effect of the outlet shroud on the weak extinction. The presence of the shroud promoted more rapid flame development and this produced a reduction in HC and CO. This also reduced the prompt NOx due to the reduction in HC. The overall NOx was reduced as the axial swirler outlet shroud diameter was reduced. The trends were the same for all three swirler vane angles, but there was little advantage of using higher swirl number large vane angle swirlers when compared at the same pressure loss. The minimum NOx at 15% oxygen for premixed combustion at 1750K with 600K inlet temperature was 2ppm for 30° shrouded axial swirlers, 3ppm for 45° shrouded swirlers and 2.5ppm for 60° shrouded swirlers. However, a 45° unshrouded axial swirler with smaller central hub and large D/d had NOx emissions of 2ppm.
Comparisons of Emissions Characteristics of Several Turbine Engines Burning Fischer-Tropsch and Hydroprocessed Esters and Fatty Acids Alternative Jet Fuels
Authors: Corporan Edwin , DeWitt Matthew J. , Klingshirn Christopher D. , Anneken David , Shafer Linda , Streibich Richard
Published: July 2013

A summary of the impacts of alternative fuel blends on the gaseous and particulate matter (PM) (mostly soot) emissions of aircraft turbine engines is presented. Six engines were studied under several US Air Force and NASA sponsored programs to assess the impacts of the alternative (non-petroleum) fuels on emissions and/or to support the certification of military aircraft for the use of 50/50 (by volume) alternative fuel/JP-8 blends. One turboshaft (T63) and five turbofan (CFM56-7, CFM56-2, F117, TF33 and PW308) engines were studied. Fuels derived from coal and natural gas produced via Fischer-Tropsch (FT) synthesis, and fuels from animal fats and plant oils produced via hydroprocessing [Hydroprocessed Esters and Fatty Acids (HEFA)] were evaluated. Trends of alternative fuel impacts on emissions compared to conventional fuel for the different engine types are discussed. Results consistently show significant reductions in PM emissions with the alternative fuel blends compared to operation with conventional fuels. These relative reductions were observed to be lower as engine power increased. Engines operated with different alternative fuel blends were found to produce similar slopes of normalized particle number to engine power with only the magnitude of the reductions being a function of the fuel type. These results suggest that it may be plausible to predict particle number emissions from turbine engines operated on alternative fuels based on engine, engine setting, limited PM data and fuel composition. Gaseous emissions measurements show modest reductions of carbon monoxide, unburned hydrocarbons and hazardous air pollutants (HAPs) with the alternative fuels for several engines; however, no clear dependency of fuel impacts based on engine characteristics were observed.
Technical Applicability of Low-Swirl Fuel Nozzle for a Liquid-Fueled Industrial Gas Turbine Combustor
Authors: Koyama Masamichi , Tachibana Shigeru
Published: July 2013

This paper explores the technical applicability of a low-swirl fuel nozzle designed for use with a liquid-fueled industrial gas turbine combustor. Particle image velocimetry was applied to measure nozzle flow fields with an open methane-air premixed flame configuration. Herein we discuss the effects of the chamfer dimensions of the nozzle tip on flow characteristics. The profiles indicate parallel shifts in axial direction that depend on chamfer dimensions. When velocity is normalized by bulk velocity and plotted against axial distance from the virtual origins, the profiles are consistent. This means that chamfer dimensions primarily affect the axial position of the flame, while keeping other flow characteristics, such as global stretch rate, unchanged. Then, the atmospheric combustion test was conducted with kerosene in a single-can combustor. Lifted flame stabilization was confirmed by observing the flames through a window. Lastly, an engine test was performed to assess the technical applicability of the fuel nozzle under real engine conditions. The engine testbed was a 290 kW simple-cycle liquid-fueled gas turbine engine. The configurations of the fuel nozzle were consistent with the ones used in the PIV and the atmospheric combustion test. Wall temperatures close to the fuel nozzle exit were within the acceptable range, even without the cooling air required with conventional combustors. This is an advantage of the lifted flame stabilization technique. NOx emissions were below maximum levels set under current Japanese regulations (<84 ppm@15% O2). In sum, the proposed fuel nozzle design shows promise for use with liquid-fueled industrial gas turbine engines.
Combustion Dynamics Validation of an Annular Reheat Combustor
Authors: Singla Ghislain , Noiray Nicolas , Schuermans Bruno
Published: July 2013

This paper deals with a detailed thermoacoustic assessment of an annular reheat combustor. Extensive tests have been conducted in the GT26 Test Power Plant in Switzerland. To this end, the combustion chamber has been instrumented with advanced pulsation sensors, an optical probe, strain gauges and accelerometers. A large number of dynamic pressure sensors recorded the acoustic pressure wave propagations in the axial and circumferential directions over a very large frequency range.

A modal analysis technique has been developed to extract the acoustic mode shapes from the experimental data. This technique allows for decomposition in standing and traveling waves, hence revealing the nature of the acoustic field. The extracted mode shapes showed a very good agreement with results from 3-d finite element calculations.

Combustion stability has been quantified by a methodology that extracts pulsation growth rates from experimental data. This novel method relies on advanced statistic processing of the instantaneous pulsation amplitudes. It has the advantage that it is insensitive to probe location, which is of particular advantage for high frequencies (higher than 1 kHz).
A Model for the Thermo-Acoustic Feedback of Transverse Acoustic Modes and Periodic Oscillations in Flame Position in Cylindrical Flame Tubes
Authors: Schwing Joachim , Grimm Felix , Sattelmayer Thomas
Published: July 2013

In the past decades, several feedback mechanisms for longitudinal acoustic modes in gas turbine combustors have been investigated. These mechanisms are successfully used in predictive tools like acoustic network models to analyze low-frequency instabilities in combustion systems. In contrast, little is known about high-frequency oscillations — fluctuations at several kHz. Most theories are derived from experimental investigations of afterburners in the 1950s and 1960s, indicating an interaction of vortex shedding, fluctuating vorticity and heat release. In this work a different feedback mechanism for high-frequency oscillations in cylindrical flame tubes related to transverse acoustic modes is suggested and analysed: Transverse acoustic pressure fluctuations are linked to an oscillating velocity field. A time-dependent but periodic displacement field can be derived from these velocity fluctuations. The model assumes that the zone of heat release is displaced by the velocity fluctuations. Pressure oscillations and periodically deflected heat release lead to a contribution to the Rayleigh criterion without fluctuations in the global heat release. This effect is studied in a circular cross section presuming a circular zone of heat release. Expressions for the displacement of the flame front are derived from the analytical solution of the wave equation in cylindrical geometries assuming a quiescent medium, constant density and speed of sound. The Rayleigh criterion is integrated and growth rates are evaluated whereas damping effects are neglected as they are not subject to this study. Characteristics of the model are assessed and compared to experimental observations to check the validity and the applicability of the theory.
Experimental and Numerical Investigation of Non-Equilibrium Plasma Assisted Combustion of Low BTU Fuels
Authors: Hu Hongbin , Nie Chaoqun , Li Gang , Fang Aibing , Cui Yufeng
Published: July 2013

This paper mainly focuses on reliable ignition and flame stabilization of low-BTU gas fuels with non-equilibrium air plasma assist. The results of experimental and numerical analyses indicated that the flame propagation speed was increased while the ignition time was decreased by the effect of non-equilibrium air plasma. Active radicals observed in air plasma made great efforts to the generation of OH radical which can accelerate the fuel oxidation process greatly.
Impact of Cooling Air Injection on the Primary Combustion Zone of a Swirl Burner
Authors: Marosky A. , Seidel V. , Bless S. , Sattelmayer T. , Magni F.
Published: July 2013

In most dry low NOx combustor designs the front panel impingement cooling air is directly injected into the combustor primary zone. As this air partially mixes with the swirling flow of premixed reactants from the burner prior to completion of heat release it reduces the effective equivalence ratio in the flame and has a beneficial effect on NOx emissions. However, the fluctuations of the equivalence ratio in the flame potentially increase heat release fluctuations and influence flame stability. Since both effects are not yet fully understood isothermal experiments are made in a water channel where high speed planar laser induced fluorescence (HSPLIF) is applied to study the cooling air distribution and its fluctuations in the primary zone. In addition the flow field is measured with high speed particle image velocimetry (HSPIV). Both, mixing and flow field are also analyzed in numerical studies using isothermal large eddy simulation (LES) and the simulation results are compared with the experimental data. Of particular interest is the influence of the injection configuration and cooling air momentum variation on the cooling air penetration and dispersion. The spatial and temporal quality of mixing is quantified with probability density functions (PDF). Based on the results regarding the equivalence ratio fluctuations regions with potential negative effects on combustion stability are identified. The strongest fluctuations are observed in the outer shear layer of the swirling flow, which exerts a strong suction effect on the cooling air. Interestingly, the cooling air dilutes the recirculation zone of the swirling flow. In the reacting case this effect is expected to lead to a decrease of the temperature in the flame anchoring zone below the adiabatic flame temperature of the premixed reactant, which may have an adverse effect on flame stability.
Experimental Study of Nitrogen Dilution Effects on a Double-Swirled Non-Premixed Syngas Burner
Authors: Ge Bing , Zang Shu-sheng , Guo Peiqing , Tian Yin-shen
Published: July 2013

The development of integrated, coal-gasification combined cycle (IGCC) systems provides cost-effective and environmentally sound options for meeting future coal-utilizing power generation needs in the world. The combustion of gasified coal fuel significantly influences overall performance of IGCC power generation. This study focuses on investigating the nitrogen dilution effects on a double-swirled non-premixed syngas flame. As the references, investigations on the H2 and CO double-swirled flames with N2 dilution are presented. Planar laser-induced fluorescence (PLIF) of OH-radical measurement is adopted to identify main reaction zones and burnt gas regions. Together with temperature and emission measurement during exhaust section, some important characteristics of the syngas flame are overall investigated. Experimental result shows that syngas flame root near the burner exit demonstrates double flame front structure. The existence of N2 expands the flame opening angle and enlarges the main reaction zone, and it may lead to lower NO emission and higher CO emission in exhaust gas.
Extended Fuel Flexibility Testing of Siemens Industrial Gas Turbines: A Novel Approach
Authors: Andersson Mats , Larsson Anders , Lindholm Annika , Larfeldt Jenny
Published: July 2013

Opportunity gaseous fuels are of great interest for small and medium sized gas turbines. The variety of gaseous fuels that Siemens Industrial Turbomachinery AB (SIT) is requested to make judgments on is continuously expanding. From such requests follows an increasing need for testing new fuels.

The SIT novel approach for fuel flexibility testing, EBIT, has been to combine the single burner rig testing with a full scale engine test to give a cost effective and flexible solution. The combination of the two approaches is accomplished by using a separate feed of testing fuel to one or more burners in a standard gas turbine installation where the other burners use standard fuel from standard fuel system for engine operation. The separate feed of testing fuel can be operated as a slave to engine governor heat demand, but can also be controlled independently.

This paper describes how EBIT has been implemented and tested. Combustion monitoring techniques and measurements to check behavior and predictions for full scale engine tests are presented. Results from testing with a blended natural gas with more than 50% of heat input from pentane, C5H12, in a SGT-700 engine shows that the EBIT concept is possible and powerful.

The SIT 3rd generation DLE burner proves to be very fuel flexible and tolerant to high levels of pentane in the fuel. Less than 20% increase in NOx emissions can be expected when using pentane rich fuels. The burner is used in the SGT-800 47MW engine and the SGT-700 31MW engine.
Thermoacoustic Stability Analysis of a Kerosene-Fueled Lean Direct Injection Combustor Employing Acoustically and Optically Measured Transfer Matrices
Authors: Bobusch Bernhard C. , Moeck Jonas P. , Paschereit Christian Oliver , Sadig Sermed
Published: July 2013

The assessment of the stability characteristics of kerosene-fueled, lean direct injection flames is an important issue for the design of low-emission aircraft engine combustion systems. To achieve this task, acoustic network models are widely used. In the present work, this technique is applied to determine the stability behavior of a liquid-fueled, lean direct injection combustor. The required transfer matrices have been measured in an atmospheric combustion test rig. The burner transfer matrix as well as the upstream and downstream reflection coefficients are obtained by using the multi-microphone method. Since the measurement of flame transfer functions for liquid-fueled flames is a complex task, two techniques are applied and compared. First, the flame response to loudspeaker forcing is measured with the multi-microphone technique. Second, a technique based on the simultaneous acquisition of different chemiluminescence signals is applied. The chemiluminescence response at four different wavelengths (310 nm, 407 nm, 431 nm, and 515 nm), corresponding to the species OH*, CH*, CO2* and C2*, respectively, are measured using photomultiplier tubes. With a calibration measurement at different operating conditions, it is possible to calculate the instantaneous heat release rate. Flame transfer functions and matrices are measured in the test rig with the two techniques. Additionally, all acoustically measured transfer matrices and optically measured transfer functions are used to predict possible unstable modes in the test rig. The experimental results and the stability analysis employing the measured flame transfer functions are in good agreement and demonstrate validity of the method.
Novel Burner Concept for Premixed Surface-Stabilized Combustion
Authors: Kornilov V. N. , Shakariyants S. , de Goey L. P. H.
Published: July 2013

Surface-stabilized combustion is credited with high burning rates, extended lean flammability limits, wide modulation range and other advantages. This makes it an attractive technology for compact low-emission combustors.

The experimental gas turbine surface burners reported to this date are produced from compressed and sintered Fe-Cr-Al fiber mats. The authors have developed a new concept of surface burner fabricated by braiding ceramic cords around a ceramic frame. This simple method produces a basket-type surface suitable for stabilizing lean premixed flames over a broad range of operating conditions. The use of ceramics extends possibilities for operation at very high inlet temperatures with reduced risks of material sintering and oxidation.

This paper presents test results with an experimental burner on a pressurized combustion rig with optical access. The experiments were performed under the following conditions: inlet temperatures of 22–740 C, pressures of 1–3 bar, thermal power between 4 kWTh and 32 kWTh and equivalence ratios of 0.28–0.95. Measurements of flue gas composition and pressure drop are also reported in the paper. The operating window for low-NOx and low-CO combustion is analyzed.

With the demonstrated performance, the burner could cover the operating envelope of a 3 kWe recuperated micro turbine [1]–[2] with no pilot and no staging. This would also limit NOx to <40 ppm @ 0% O2 within the micro turbine load range of 100% to 50%.
Hydrogen Combustion Within a Gas Turbine Reheat Combustor
Authors: Poyyapakkam Madhavan , Wood John , Mayers Steven , Ciani Andrea , Guethe Felix , Syed Khawar
Published: July 2013

This paper describes a novel lean premixed reheat burner technology suitable for Hydrogen-rich fuels. The inlet temperature for such a combustor is very high and reaction of the fuel/oxidant mixture is initiated through auto-ignition, the delay time for which reduces significantly for Hydrogen-rich fuels in comparison to natural gases. Therefore the residence time available for premixing within the burner is reduced. The new reheat burner concept has been optimized to allow rapid fuel/oxidant mixing, to have a high flashback margin and to limit the pressure drop penalty.

The performance of the burner is described, initially in terms of its fluid dynamic properties and then its combustion characteristics. The latter are based upon full-scale high-pressure tests, where results are shown for two variants of the concept, one with a pressure drop comparable to today’s natural gas burners, and the other with a two-fold increase in pressure drop. Both burners indicated that Low NOx emissions, comparable to today’s natural gas burners, were feasible at reheat engine conditions (ca. 20 Bars and ca. 1000C inlet temperature). The higher pressure drop variant allowed a wider operating window. However the achievement of the lower pressure drop burner shows that the targeted Hydrogen-rich fuel (70/30 H2/N2 by volume) can be used within a reheat combustor without any penalty on gas turbine performance.
Injection of Liquid Kerosene Into a High-Pressure Subsonic Air Crossflow From Normal Temperature to Elevated Temperature
Authors: Li Lin , Lin Yuzhen , Xue Xin , Gao Wei , Sung Chih-Jen
Published: July 2013

In the present work, injection of liquid kerosene into a high-pressure subsonic air crossflow was investigated experimentally. Tests were conducted at air pressures up to 2.0 MPa and at air temperatures from normal temperature to elevated temperature. Liquid kerosene was injected at room temperature through a 0.5 mm diameter plain orifice. Schlieren imaging technique was used for jet structure visualization, from which the jet penetration trajectory was determined by the image processing. For the conditions tested, a correlation of jet penetration trajectory was developed, with momentum flux ratio, Weber number and crossflow temperature ratio as independent variables. Upper surface trajectories of kerosene spray under different test conditions were compared. Experimental and analytical results showed that the penetration trajectory of liquid kerosene under higher air temperature was greater than that under normal temperature, while momentum ratios were the same.
Comparison of Two Methods for Flame Transfer Function Measurements: MOOG Valve or Siren and the Impact of Results on the Instability Analysis in a High Pressure Combustor
Authors: Kapucu M. , Kok J. B. W. , Alemela P. R.
Published: July 2013

Thermoacoustic instabilities may occur in every gas turbine combustor and could be hazardous to the flame stability and the structural integrity. It is important to be able to predict how hazardous the instabilities are: at what frequencies will they occur and will they develop into high amplitude limit cycle oscillations? The former question can be answered with the help of the Flame Transfer Function (FTF). The FTF establishes the coupling between burner passage aerodynamics and combustion dynamics and can be used as an input to an acoustic model to predict the eigenfrequencies and their growth rate. In the present research two methods to measure the FTF are used with different signal excitation instruments: a MOOG Valve and a Siren. Both the methods are based on data from pressure transducers only. The FTF is measured here by determining the combustor pressure response of the flame to fluctuations in the fuel mass flow at the burner exit. A siren unit has been developed and mounted at the upstream end of the fuel supply line of a pressurized combustor and is designed to have a harmonic excitation. The experimental method to measure the FTF by means of factorization in known or measurable sub-functions is briefly explained. Subsequently the Siren method is demonstrated by means of extracting the FTF at elevated pressure and as a function of thermal power. The results are compared with the results obtained in previous work of a MOOG valve excitation unit. The experimental investigation of the FTF is carried out in a high pressure combustor rig named DESIRE which is able to perform thermoacoustic measurements up to 500 kW thermal power at 5 bar absolute pressure. The results are compared and discussed. Subsequently a 1-D acoustic network model is presented which predicts the onset of the limit cycle pressure oscillations in the DESIRE combustor, using the FTF as an input. Thermo viscous damping effects and measured reflection coefficients are also included into the network model to improve the model predictions. Finally, the measured and predicted dynamic behavior of the combustor are compared. The results indicate that the network modeling approach is a promising design tool as it gives good agreement between measured and predicted dynamic behavior of the combustor and instability analysis. Well-defined boundary conditions and thermo viscous damping effects are important for the accuracy of the acoustic network models.
Laminar Flame Speed and Ignition Delay Time Data for the Kinetic Modeling of Hydrogen and Syngas Fuel Blends
Authors: Krejci M. C. , Mathieu O. , Vissotski A. J. , Ravi S. , Sikes T. G. , Petersen E. L. , Keromnes A. , Metcalfe W. , Curran H. J.
Published: July 2013

Laminar flame speeds and ignition delay times have been measured for hydrogen and various compositions of H2/CO (syngas) at elevated pressures and elevated temperatures. Two constant-volume cylindrical vessels were used to visualize the spherical growth of the flame through the use of a schlieren optical setup to measure the laminar flame speed of the mixture. Hydrogen experiments were performed at initial pressures up to 10 atm and initial temperatures up to 443 K. A syngas composition of 50/50 by volume was chosen to demonstrate the effect of carbon monoxide on H2−O2 chemical kinetics at standard temperature and pressures up to 10 atm. All atmospheric mixtures were diluted with standard air, while all elevated-pressure experiments were diluted with a He:O2 of 7:1 to minimize instabilities. The laminar flame speed measurements of hydrogen and syngas are compared to available literature data over a wide range of equivalence ratios where good agreement can be seen with several data sets. Additionally, an improved chemical kinetics model is shown for all conditions within the current study. The model and the data presented herein agree well, which demonstrates the continual, improved accuracy of the chemical kinetic model.

A high-pressure shock tube was used to measure ignition delay times for several baseline compositions of syngas at three pressures across a wide range of temperatures. The compositions of syngas (H2/CO) by volume presented in this study included 80/20, 50/50, 40/60, 20/80, and 10/90, all of which are compared to previously published ignition delay times from a hydrogen-oxygen mixture to demonstrate the effect of carbon monoxide addition. Generally, an increase in carbon monoxide increases the ignition delay time, but there does seem to be a pressure dependency. At low temperatures and pressures higher than about 12 atm, the ignition delay times appear to be indistinguishable with an increase in carbon monoxide. However, at high temperatures the relative composition of H2 and CO has a strong influence on ignition delay times. Model agreement is good across the range of the study, particularly at the elevated pressures. Also, an increase in carbon monoxide causes the activation energy of the mixture to decrease.
Study of Fuel Composition Effects on Flashback Using a Confined Jet Flame Burner
Authors: Shaffer Brendan , Duan Zhixuan , McDonell Vincent
Published: July 2013

Flashback is the main operability issue associated with converting lean, premixed combustion systems from operation on natural gas to operation on high hydrogen content fuels. Most syngas fuels contain some amount of hydrogen (15–100%) depending on the fuel processing scheme. With this variability in the composition of syngas, the question of how fuel composition impacts flashback propensity arises. To address this question, a jet burner configuration was used to develop systematic data for a wide range of compositions under turbulent flow conditions. The burner consisted of a quartz burner tube confined by a larger quartz tube. The use of quartz allowed visualization of the flashback processes occurring. Various fuel compositions of hydrogen, carbon monoxide, and natural gas were premixed with air at equivalence ratios corresponding to constant adiabatic flame temperatures (AFT) of 1700 K and 1900 K. Once a flame was stabilized on the burner, the air flow rate would be gradually reduced while holding the AFT constant via the equivalence ratio until flashback occurred. Schlieren and intensified OH* images captured at high speeds during flashback allowed some additional understanding of what is occurring during the highly dynamic process of flashback. Confined and unconfined flashback data were analyzed by comparing data collected in the present study with existing data in the literature. A statistically designed test matrix was used which allows analysis of variance of the results to be carried out, leading to correlation between fuel composition and flame temperature with (1) critical flashback velocity gradient and (2) burner tip temperature. Using the burner tip temperature as the unburned temperature in the laminar flame speed calculations showed increased correlation of the flashback data and laminar flame speed as opposed to when the actual unburned gas temperature was used.
Experimental Study on Combustion Characteristics of Conventional and Alternative Liquid Fuels
Authors: Vukadinovic Vlade , Habisreuther Peter , Zarzalis Nikolaos
Published: July 2013

Gas turbine combustor design relies strongly on the turbulent flame velocity over the whole turbine operation range. Due to the fact that turbulent flame velocity depends strongly on the laminar one, its characterisation at different thermodynamic conditions is necessary for further optimisation of gas turbines. The Markstein number, which quantifies the response of the flame to the stretch, also has to be considered. Additionally, the Markstein number can be utilised as an indicator for laminar and turbulent flame front stability.

The current attempts to replace conventional fuels, such as kerosene, with alternative ones, obtrude their comparison in order to find the most appropriate substitute. Additionally, significant differences in the flame behaviour, which could be recognised through different combustion characteristics, can lead to modification of currently used gas turbine design. Even so, the experimental data of alternative fuels are scarce, especially at elevated pressure conditions.

So, the combustion characteristics, laminar burning velocity and Markstein number of kerosene Jet A-1 and several alternative fuels (GTL and GTL blends) are investigated experimentally in an explosion vessel. For this purpose an optical laser method is employed based on the Mie-scattering of the laser light by smoke particles. Within this experimental study the influence of three crucial parameters: initial temperature, initial pressure and mixture composition on the burning velocity and Markstein number are investigated. The experiments were performed at three different pressures 1, 2, 4bar; three different temperatures 100°C, 150°C, 200°C; and for a range of equivalence ratio 0.67–1.67. The observed results are compared and discussed in detail.
Adaptive NOx Control on Refinery Gas in Industrial Gas Turbines
Authors: Geipel Philipp , Bjerklund Erik , Persson Magnus , Carrera Arturo Manrique
Published: July 2013

The current work explores the operation of an industrial gas turbine (25 MWe) unit working under variable NOx emission limits (from 75 to 120 mg/Nm3) and variable fuel composition. The latter is typical for flared streams in oil process industry (refineries/well operation/petrochemicals).

In the current case the nitrous oxides (NOx) emission limits are dependent on the mixing ratio of natural gas (NG, 89%vol. methane) and refinery gas (RG, 40% vol. H2, 56%vol. CH4, C4+) that is used as fuel for the engine. This mixture is process dependent and varies in matter of minutes from 100% NG to 100% RG. Siemens has faced this challenge by using a SGT-600 unit (25MWe) operating in non-premixed combustion mode with a novel water injection strategy, the adaptive water injection for the control of NOx.

The adaptive water injection for NOx control has been developed after evaluating different NOx control strategies. It consists of a closed loop, in which NOx emission measurements are used as the main control parameter, linked to a fixed parametric curve based on the compressor discharge pressure. Fast response times and fail–safe strategies have also been developed and tested under operating conditions of the GT. The water injection method could cope with the variation of load, fuel supply mixture and NOx limit without any flame instability problems. This is done while maintaining the optimal amount of water needed to achieve the emissions target. The robustness of the system has been satisfactory over the tested period and seems a viable solution.
Comparison of Nonlinear to Linear Thermoacoustic Stability Analysis of a Gas Turbine Combustion System
Authors: Krebs Werner , Krediet Harmen , Portillo Enrique , Hermeth Sebastian , Poinsot Thierry , Schimek Sebastian , Paschereit Oliver
Published: July 2013

Gas turbines offer a high operational flexibility and a good turn down ratio to meet future requirements of power production. In this context stable operation over a wide range and for different blends of fuel is requested. Thermoacoustic stability assessment is crucial for accelerating the development and implementation of new combustion systems.

The results of nonlinear and linear thermoacoustic stability assessments are compared on basis of recent measurements of flame describing functions and thermoacoustic stability of a model swirl combustor operating in the fully turbulent regime. The different assessment methods are outlined. The linear thermoacoustic stability assessment yields growth rates of the thermoacoustic instability whereas the limit cycle amplitude is predicted by the nonlinear stability method.

It could be shown that the predicted limit cycle amplitudes correlate well with the growth rates of excitation obtained from linear modeling. Hence for screening the thermoacoustic stability of different design approaches a linear assessment may be sufficient while for detailed prediction of the dynamic pressure amplitude more efforts have to be spent on the nonlinear assessment including the analysis of the nonlinear flame response.
Evaluation of Transport Line Effects on PM Size Distribution for Aircraft Exhaust for Different Flow Regimes and Dilution Methodology
Authors: Sevcenco Yura A. , Walters David , Crayford Andrew P. , Marsh Richard , Bowen Philip J. , Johnson Mark P.
Published: July 2013

This study is part of an ongoing European Aviation Safety Agency (EASA) programme (‘SAMPLE’). The effects of gas stream flow regimes in the sample transport line and dilution strategies for removal of the volatile fraction on measured PM size distribution are evaluated behind a simulated aero-derivative gas turbine exhaust using a fast mobility DMS500 particle sizer. The PM size distribution and concentration within the primary transport sample was found to be relatively insensitive to flow regime, with conditions of turbulent flow (lowest residence time) providing the highest number concentrations, and hence least losses. However, given the natural variation of PM production from the combustor source the statistical certainty of these observations require consolidation. A ‘bespoke’ volatile particle removal system based on the European automotive PMP protocol was constructed to allow the effects of dilution ratio and evaporation tube residence time to be investigated. It was shown that both strategies of increasing dilution ratio and residence times in the evaporation tube did not affect the size distribution at the two distinct nucleation and accumulation modes to any statistical certainty. When using high (420:1) dilution ratios in the VPR, a third larger (200nm) mode appears, which requires further investigation.
Modeling CO With Flamelet-Generated Manifolds: Part 1—Flamelet Configuration
Authors: Goldin Graham , Ren Zhuyin , Forkel Hendrik , Lu Liuyan , Tangirala Venkat , Karim Hasan
Published: July 2013

In laminar flamelet modeling, a laminar flame in a simple 0D or 1D configuration is calculated a-priori and parameterized by a few scalars such as mixture fraction and reaction-progress or strain-rate. Transport equations, or algebraic expressions, for these parameters are then solved in 3D CFD simulations, avoiding computationally expensive in-situ chemical kinetic calculations. Typical configurations for laminar flamelets include, in 1D, opposed flow configurations with either non-premixed or premixed streams, freely propagating premixed flames, premixed flames impinging on a (heated) wall, and burner stabilized premixed flames. In 0D, plug-flow, perfectly-stirred (PSR) and partially-stirred reactors have been employed to build ‘flamelet-like’ ignition and flame-propagation tables. This paper compares 1D strained steady and unsteady non-premixed flamelets, 1D strained premixed flamelets, and 0D PSR simulations at a stochiometric and a lean equivalence ratio. At stochiometric mixtures, all three flamelet configurations show comparable manifolds (i.e. CO and OH mass fractions, and reaction-progress source term distributions). However, at lean equivalence ratios, the different configurations show substantially different manifolds. It is concluded that a unique flamelet configuration cannot be identified for a general partially-premixed model that ranges from the non-premixed to the perfectly premixed limit. Instead, to accurately model CO emissions, it may be necessary to include both premixed and non-premixed flamelets, with a flame-index (e.g. Yamashita et al., 1996, Proc. Combust. Inst., 26) to select the appropriate burning regime.
Correlations for Turbulent Flame Speed of Different Syngas Mixtures at High Pressure and Temperature
Authors: Daniele S. , Jansohn P.
Published: July 2013

There is an obvious lack of data and understanding of the behavior of turbulent flames at high temperature and high pressure, especially concerning hydrogen containing fuels. Among the many relevant parameters, the turbulent flame speed “ST” is one of the most interesting for scientists and engineers.

This paper reports an experimental investigation of premixed syngas combustion at gas-turbine like conditions, with emphasis on the determination of ST/SL derived as global fuel consumption per unit time. Experiments at pressures up to 2.00 MPa, inlet temperatures and velocities up to 773K and 150 m/s respectively, u′/SL greater than 100 are presented. Comparison between different syngas mixtures and methane clearly show much higher ST/SL for the former fuel. It is shown that ST/SL is strongly dependent on preferential diffusive-thermal (PDT) effects, co-acting with hydrodynamic effects, even for very high u′/SL. ST/SL increases with rising hydrogen content in the fuel mixture and with pressure. A correlation for ST/SL valid for all investigated fuel mixtures, including methane, is proposed in terms of turbulence properties (turbulence intensity and integral length scale), combustion properties (laminar flame speed and laminar flame thickness) and operating conditions (pressure and inlet temperature). The correlation captures effects of preferential diffusive-thermal and hydrodynamic instabilities.
Characterization of the Acoustic Interactions in a Two-Staged Multi-Injection Combustor Fed With Liquid Fuel
Authors: Providakis T. , Zimmer L. , Scouflaire P. , Ducruix S.
Published: July 2013

Burners operating in lean premixed prevaporized (LPP) regimes are considered as good candidates to reduce pollutant emissions from gas turbines. Lean combustion regimes result in lower burnt gas temperatures and therefore a reduction on the NOx emissions, one of the main pollutant species. However, these burners usually show strong flame dynamics, making them prone to various stabilization problems (combustion instabilities, flashback, flame extinction). To face this issue, multi-injection staged combustion can be envisaged. Staging procedures enable fuel distribution control, while multipoint injections can lead to a fast and efficient mixing. A laboratory-scale staged multipoint combustor is developed in the present study, in the framework of LPP combustion, with an injection device close to the industrial one. Using a staging procedure between the primary pilot stage and the secondary multipoint one, droplet and velocity field distributions can be varied in the spray that is formed at the entrance of the combustion chamber. The resulting spray and the flame are characterized using OH-Planar Laser Induced Fluorescence, High Speed Particle Image Velocimetry and Phase Doppler Anemometry measurements. Three staging values, corresponding to three different flame stabilization processes, are analyzed, while power is kept constant. It is shown that mean values are strongly influenced by the fuel distribution and the flame position. Using adequate post-processing, the interaction between the acoustic field and the droplet behavior is characterized. Spectral analysis reveals a strong acoustic-flame coupling leading to a low frequency oscillation of both the velocity field and the spray droplet distribution. In addition, acoustic measurements in the feeding line show that a strong oscillation of the acoustic field leading to a change in fuel injection, and hence droplet behavior.