Influence of Boundary Layer Air Injection on Flashback of Premixed Hydrogen-Air Flames

2016 ◽  
Author(s):  
Vera Hoferichter ◽  
Payam Mohammadzadeh Keleshtery ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer ◽  
Yoshikazu Matsumura
Keyword(s):  
Boundary Layer ◽  
Mass Flow ◽  
Carbon Dioxide Emissions ◽  
Gas Turbines ◽  
Structural Damage ◽  
Alternative Fuels ◽  
Air Injection ◽  
Current Standard ◽  
Reference Case ◽  
Flame Flashback

Alternative fuels like hydrogen are presently discussed as one possibility to reduce carbon dioxide emissions from gas turbines. Premixed lean combustion is a current standard to minimize nitrogen oxide emissions. However, the early mixing of fuel and oxidizer upstream of the combustion chamber opens up the possibility of upstream flame propagation, referred to as flame flashback. Flame flashback in gas turbines has to be prevented as it leads to immediate engine shut down or even structural damage. Due to high burning velocities and low quenching distances, flashback is especially critical in premixed hydrogen flames. In particular, the low velocity region near the burner wall promotes flashback. Diluting the mixture near the wall by fluid injection is one approach to counteract this phenomenon and to enhance the safe operating range of a gas turbine burner. This article presents an experimental study on the effect of air injection on flame flashback investigated at a channel burner configuration. Different injection mass flow rates, positions and angles are compared to a reference case without injection regarding their flashback limits. The effectiveness of the injection increases with the injected mass flow rate. The resulting flashback limits can be correlated with the equivalence ratio at the wall by concepts taken from film cooling. However, the fluid injector is a source of boundary layer disturbances leading to an initial penalty regarding flashback resistance. This penalty increases the closer the injector is located to the burner exit. Furthermore, the penalty increases for lower injection angles as the area of the injector and the corresponding boundary layer disturbances increase.

scholarly journals Computational Modeling of Boundary Layer Flashback in a Swirling Stratified Flame Using a LES-Based Non-Adiabatic Tabulated Chemistry Approach

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 567
Author(s):  
Xudong Jiang ◽  
Yihao Tang ◽  
Zhaohui Liu ◽  
Venkat Raman
Keyword(s):  
Boundary Layer ◽  
Heat Loss ◽  
Boundary Layers ◽  
Gas Turbines ◽  
Predictive Accuracy ◽  
Safety Issue ◽  
Combustion Model ◽  
Tabulated Chemistry ◽  
Lean Fuel ◽  
Flame Flashback

When operating under lean fuel–air conditions, flame flashback is an operational safety issue in stationary gas turbines. In particular, with the increased use of hydrogen, the propagation of the flame through the boundary layers into the mixing section becomes feasible. Typically, these mixing regions are not designed to hold a high-temperature flame and can lead to catastrophic failure of the gas turbine. Flame flashback along the boundary layers is a competition between chemical reactions in a turbulent flow, where fuel and air are incompletely mixed, and heat loss to the wall that promotes flame quenching. The focus of this work is to develop a comprehensive simulation approach to model boundary layer flashback, accounting for fuel–air stratification and wall heat loss. A large eddy simulation (LES) based framework is used, along with a tabulation-based combustion model. Different approaches to tabulation and the effect of wall heat loss are studied. An experimental flashback configuration is used to understand the predictive accuracy of the models. It is shown that diffusion-flame-based tabulation methods are better suited due to the flashback occurring in relatively low-strain and lean fuel–air mixtures. Further, the flashback is promoted by the formation of features such as flame tongues, which induce negative velocity separated boundary layer flow that promotes upstream flame motion. The wall heat loss alters the strength of these separated flows, which in turn affects the flashback propensity. Comparisons with experimental data for both non-reacting cases that quantify fuel–air mixing and reacting flashback cases are used to demonstrate predictive accuracy.

Boundary Layer Flashback in Premixed Hydrogen–Air Flames With Acoustic Excitation

2017 ◽  
Vol 140 (5) ◽  
Author(s):  
Vera Hoferichter ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Flow Velocity ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Excitation Amplitude ◽  
Bulk Flow ◽  
Acoustic Excitation ◽  
Worst Case ◽  
Thermoacoustic Instabilities ◽  
Flame Flashback

Lean premixed combustion is prevailing in gas turbines to minimize nitrogen oxide emissions. However, this technology bears the risk of flame flashback and thermoacoustic instabilities. Thermoacoustic instabilities induce velocity oscillations at the burner exit which, in turn, can trigger flame flashback. This article presents an experimental study at ambient conditions on the effect of longitudinal acoustic excitation on flashback in the boundary layer of a channel burner. The acoustic excitation simulates the effect of thermoacoustic instabilities. Flashback limits are determined for different excitation frequencies characterizing intermediate frequency dynamics in typical gas turbine combustors (100–350 Hz). The excitation amplitude is varied from 0% to 36% of the burner bulk flow velocity. For increasing excitation amplitude, the risk of flame flashback increases. This effect is strongest at low frequencies. For increasing excitation frequency, the influence of the velocity oscillations decreases as the flame has less time to follow the changes in bulk flow velocity. Two different flashback regimes can be distinguished based on excitation amplitude. For low excitation amplitudes, flashback conditions are reached if the minimum flow velocity in the excitation cycle falls below the flashback limit of unexcited unconfined flames. For higher excitation amplitudes, where the flame starts to periodically enter the burner duct, flashback is initiated if the maximum flow velocity in the excitation cycle is lower than the flashback limit of confined flames. Consequently, flashback limits of confined flames should also be considered in the design of gas turbine burners as a worst case scenario.

Effect of position of radial air injection plane on control of thermo-acoustic instability using active closed-loop method

2021 ◽  
pp. 107754632110501
Author(s):  
Nilaj N Deshmukh ◽  
Afzal Ansari ◽  
Praseed Kumar ◽  
Allen V George ◽  
Febin J Thomas ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Structural Damage ◽  
Closed Loop ◽  
Control Method ◽  
Heat Waves ◽  
Air Injection ◽  
Rocket Engines ◽  
Acoustic Instability ◽  
Loop Method ◽  
Short Time

Thermo-acoustic instability occurs when self-excited oscillations are generated due to the coupling between unsteady heat release and acoustics. This phenomenon can result in an increased rate of vibration, structural damage, and produces unwanted emissions. Thermo-acoustic instability occurs in rocket engines, gas turbines, combustors, and furnaces. When thermo-acoustic instability occurs, many modes are developed naturally at a specific point. Some waves are unstable and some are stable. So, to study this phenomenon the most unstable waves are considered and a technique is developed to suppress these unstable waves. A radial air injector as a closed-loop active control method is used for breaking the coupling between the heat waves and acoustics inside the 1D combustion chamber. The distance between the burner and the air injector is varied for the fixed position of the burner with respect to the Rijke tube, that is, x/L = 0.01125, 0.0075, and 0.00375. This closed-loop method works based on the feedback acquired from a microphone. The control method is built using DAQ and Arduino with the LabVIEW as interface for Arduino (LIFA). An air flow rate controller setup is developed to control and measure air required for suppressing the thermo-acoustic instability. Thermo-acoustic instability is effectively suppressed with the help of radial injection in the form of micro-jets at the downstream of the burner as the closed-loop controlling method. It is concluded that when the radial micro-jet air injection plane is closer to the burner head, the thermo-acoustic instability gets suppressed in a short time and with a lesser quantity of air.

scholarly journals Local Green Power Supply Plants Based on Alcohol Regenerative Gas Turbines: Economic and Environmental Aspects

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2156 ◽  
Author(s):  
Oleksandr Cherednichenko ◽  
Valerii Havrysh ◽  
Vyacheslav Shebanin ◽  
Antonina Kalinichenko ◽  
Grzegorz Mentel ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Gas Turbine ◽  
Carbon Dioxide Emissions ◽  
Gas Turbines ◽  
Alternative Fuels ◽  
Fossil Fuels ◽  
Waste Heat ◽  
Turbine Engine ◽  
Engine Efficiency ◽  
Conversion Performance

Growing economies need green and renewable energy. Their financial development can reduce energy consumption (through energy-efficient technologies) and replace fossil fuels with renewable ones. Gas turbine engines are widely used in transport and industry. To improve their economic attractiveness and to reduce harmful emissions, including greenhouse gases, alternative fuels and waste heat recovery technologies can be used. A promising direction is the use of alcohol and thermo-chemical recuperation. The purpose of this study is to estimate the economic efficiency and carbon dioxide emissions of an alcohol-fueled regenerative gas turbine engine with thermo-chemical recuperation. The carbon dioxide emissions have been determined using engine efficiency, fuel properties, as well as life cycle analysis. The engine efficiency was maximized by varying the water/alcohol ratio. To evaluate steam fuel reforming for a certain engine, a conversion performance factor has been suggested. At the optimal water/methanol ratio of 3.075 this technology can increase efficiency by 4% and reduce tank-to-wake emission by 80%. In the last 6 months of 2019, methanol prices were promising for power and cogeneration plants in remote locations. The policy recommendation is that local authorities should pay attention to alcohol fuel and advanced turbines to curb the adverse effects of burning petroleum fuel on economic growth and the environment.

Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors—Additional Findings

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Taher Halawa
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Stable Condition ◽  
Tangential Direction ◽  
Air Injection ◽  
Centrifugal Compressors ◽  
Injection Angle ◽  
Stall Control

This study presents additional important findings to the results of the research paper; “Optimization of the efficiency of stall control using air injection for centrifugal compressors” published in the Journal of Engineering for Gas Turbines and Power in 2015 (Halawa, T., Gadala, M. S., Alqaradawi, M., and Badr, O., 2015, “Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors,” ASME J. Eng. Gas Turbines Power, 137(7), p. 072604). The aim of this study is to make a fine determination of the injection angle, which provides the best stable condition when the compressor operates close to stall condition. A relatively narrower range of injection angles with smaller intervals was selected comparing to the results of the referred published paper, which clarified that the best injection angle is 30 deg. External air was injected close to the diffuser entrance at the shroud surface. Injection was applied with mass flow rate equals 1.5% of the design compressor inlet mass flow rate with injection angles ranged from 16 deg to 34 deg measured from the tangential direction at the vaneless region. It was found that both of injection angles of 28 deg and 30 deg achieved the best results in terms of compressor stabilization but each one of them has a specific advantage comparing to the other one. Using injection angle of 28 deg provided the lowest kinetic energy losses while the best orientation of the fluid through diffuser resulted when using an injection angle of 30 deg.

Time Scale Model for the Prediction of the Onset of Flame Flashback Driven by Combustion Induced Vortex Breakdown (CIVB)

2009 ◽  
Author(s):  
Marco Konle ◽  
Thomas Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Mass Flow ◽  
Time Scale ◽  
Gas Turbines ◽  
Vortex Breakdown ◽  
High Mass ◽  
Recent Analysis ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Flame Flashback

Flame flashback driven by Combustion Induced Vortex Breakdown (CIVB) represents one of the most severe reliability problems of modern gas turbines with swirl stabilized combustors. Former experimental investigations of this topic with a 500 kW burner delivered a model for the prediction of the CIVB occurrence for moderate to high mass flow rates. This model is based on a time scale comparison. The characteristic time scales were chosen following the idea that quenching at the flame tip is the dominating effect preventing upstream flame propagation in the center of the vortex flow. Additional numerical investigations showed that the relative position of the flame regarding the recirculation zone influences the interaction of flame and flow field. The recent analysis of turbulence and chemical reaction of data acquired with high speed measurement techniques applied during the CIVB driven flame propagation by the authors lead to the extension of the prediction model. As at the flame tip the corrugated flames regime prevails at low to moderate mass flow rates, a more precise prediction in this range of mass flow rates is achieved using a characteristic burnout time τb∼1/Sl for the reactive volume. The paper presents first this new idea, confirms it then with numerical as well as experimental data and extends finally the former model to a prediction tool that can be applied in the full mass flow range of swirl burners.

Boundary Layer Flashback in Premixed Hydrogen-Air Flames With Acoustic Excitation

2017 ◽  
Author(s):  
Vera Hoferichter ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Flow Velocity ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Excitation Amplitude ◽  
Bulk Flow ◽  
Acoustic Excitation ◽  
Worst Case ◽  
Thermoacoustic Instabilities ◽  
Flame Flashback

Lean premixed combustion is prevailing in gas turbines to minimize nitrogen oxide emissions. However, this technology bears the risk of flame flashback and thermoacoustic instabilities. Thermoacoustic instabilities induce velocity oscillations at the burner exit which, in turn, can trigger flame flashback. This article presents an experimental study at ambient conditions on the effect of longitudinal acoustic excitation on flashback in the boundary layer of a channel burner. The acoustic excitation simulates the effect of thermoacoustic instabilities. Flashback limits are determined for different excitation frequencies characterizing intermediate frequency dynamics in typical gas turbine combustors (100–350 Hz). The excitation amplitude is varied from 0 to 36 % of the burner bulk flow velocity. For increasing excitation amplitude, the risk of flame flashback increases. This effect is strongest at low frequencies. For increasing excitation frequency the influence of the velocity oscillations decreases as the flame has less time to follow the changes in bulk flow velocity. Two different flashback regimes can be distinguished based on excitation amplitude. For low excitation amplitudes flashback conditions are reached if the minimum flow velocity in the excitation cycle falls below the flashback limit of unexcited unconfined flames. For higher excitation amplitudes, where the flame starts to periodically enter the burner duct, flashback is initiated if the maximum flow velocity in the excitation cycle is lower than the flashback limit of confined flames. Consequently, flashback limits of confined flames should also be considered in the design of gas turbine burners as a worst case scenario.

Time Scale Model for the Prediction of the Onset of Flame Flashback Driven by Combustion Induced Vortex Breakdown

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
M. Konle ◽  
T. Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Mass Flow ◽  
Time Scale ◽  
Gas Turbines ◽  
Vortex Breakdown ◽  
High Mass ◽  
Recent Analysis ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Flame Flashback

Flame flashback driven by combustion induced vortex breakdown (CIVB) represents one of the most severe reliability problems of modern gas turbines with swirl stabilized combustors. Former experimental investigations of this topic with a 500 kW burner delivered a model for the prediction of the CIVB occurrence for moderate to high mass flow rates. This model is based on a time scale comparison. The characteristic time scales were chosen following the idea that quenching at the flame tip is the dominating effect preventing upstream flame propagation in the center of the vortex flow. Additional numerical investigations showed that the relative position of the flame regarding the recirculation zone influences the interaction of the flame and flow field. The recent analysis on turbulence and chemical reaction of data acquired with high speed measurement techniques applied during the CIVB driven flame propagation by the authors lead to the extension of the prediction model. As the corrugated flame regimes at the flame tip prevails at low to moderate mass flow rates, a more precise prediction in this range of mass flow rates is achieved using a characteristic burnout time τb∼1/Sl for the reactive volume. This paper presents first this new idea, confirms it then with numerical as well as experimental data, and extends finally the former model to a prediction tool that can be applied in the full mass flow range of swirl burners.

Experimental Investigation on the Effect of Boundary Layer Fluid Injection on the Flashback Propensity of Premixed Hydrogen-Air Flames

2013 ◽  
Author(s):  
Georg Baumgartner ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Main Flow ◽  
Air Injection ◽  
Fluid Injection ◽  
Wall Region ◽  
Burner Exit ◽  
Wall Boundary Layer ◽  
Air Jet ◽  
Wall Boundary ◽  
Flame Flashback

Premixed combustion systems show potential to meet future regulations on nitrogen oxide emissions. However, premixed systems always involve the risk of flame flashback into the premixing section. From a gas turbine manufacturer’s point of view it is desirable to broaden the safe operating range, in particular with respect to flame flashback. It has been reported in the literature that flashback along the wall boundary layer represents the most critical failure mechanism for many burner configurations using hydrogen-rich fuels. This paper focuses on the effect of fluid injection into the wall boundary layer on the flashback propensity of a hydrogen-air jet burner. For this purpose, an experiment with a tube burner was designed, where the flame is anchored in the free atmosphere at the burner exit. Pure air was injected through an annular gap at three streamwise locations upstream of the stable flame position and at two different angles — perpendicular and at 45° to the main flow direction, respectively. The turbulent flashback limits for fully premixed hydrogen-air mixtures at atmospheric conditions were measured for a variety of equivalence ratios and different amounts of air injection. It turned out that there is a significant increase in flashback stability with injection devices close to the burner exit. The main reason for this behavior is the dilution of the mixture in the near-wall region and the resulting reduction of the flame speed. The positive effect diminishes quickly with increasing distance between flame and injection location due to considerable mixing of injected flow and main flow. This has been verified by RANS simulations. The simulations also showed that the momentum generated by the injection into the boundary layer has negligible influence on the flashback limits. It was also found that the fluid injection is not capable of stopping the upstream flame propagation once the flame has entered the tube. A probable explanation for this effect is the change from open flame holding at the burner exit to the confined flame situation inside the tube during flashback. The latter is known to substantially increase the flashback propensity, which cannot be counteracted by air injection.

Boundary Layer Flashback Limits of Hydrogen-Methane-Air Flames in a Generic Swirl Burner at Gas Turbine Relevant Conditions

2021 ◽  
Author(s):  
Dominik Ebi ◽  
Peter Jansohn
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Wall Temperature ◽  
Gas Turbines ◽  
Cooling System ◽  
Atmospheric Conditions ◽  
Preheat Temperature ◽  
Swirl Burner ◽  
Wide Range ◽  
Flame Flashback

Abstract Operating stationary gas turbines on hydrogen-rich fuels offers a pathway to significantly reduce greenhouse gas emissions in the power generation sector. A key challenge in the design of lean-premixed burners, which are flexible in terms of the amount of hydrogen in the fuel across a wide range and still adhere to the required emissions levels, is to prevent flame flashback. However, systematic investigations on flashback at gas turbine relevant conditions to support combustor development are sparse. The current work addresses the need for an improved understanding with an experimental study on boundary layer flashback in a generic swirl burner up to 7.5 bar and 300°C preheat temperature. Methane-hydrogen-air flames with 50 to 85% hydrogen by volume were investigated. Flashback limits are reported in terms of the equivalence ratio for a given pressure, preheat temperature, bulk flow velocity and hydrogen content. The wall temperature of the center body along which the flame propagated during flashback events has been controlled by an oil heating/cooling system. This way, the effect any of the control parameters, e.g. pressure, had on the flashback limit was de-coupled from the otherwise inherently associated change in heat load on the wall and thus change in wall temperature. The results show that the preheat temperature has a weaker effect on the flashback propensity than expected. Increasing the pressure from atmospheric conditions to 2.5 bar strongly increases the flashback risk, but hardly affects the flashback limit beyond 2.5 bar.

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