Flame stabilization mechanisms and shape transitions in a 3D printed, hydrogen enriched, methane/air low-swirl burner

The introduction of hydrogen into natural gas systems for environmental benefit presents potential operational issues for gas turbine combustion and power generation applications; in particular acceptable blending concentrations are still widely debated. The use of a generic swirl burner under conditions pertinent to a gas turbine combustor is therefore advantageous to (i) provide evidence of potential design modifications to inform future gas turbine operation on hydrogen blends and (ii) validate numerical model predictions. Building on a previous experimental combustion database consisting of methane-hydrogen fuel blends under atmospheric and elevated ambient conditions, a new scaled generic swirl burner has been designed for experimental investigation of flame stability and exhaust gas emissions at combustor inlet temperatures to 573 K, pressures to 0.33 MPa, and thermal powers to 126 kW. The geometry downstream of the modular burner is developed further to enable separate investigation under isothermal and combustion conditions of the influence of combustor outlet geometry and the effect of changing geometric swirl number. The burner confinement is modified to include both a cylindrical exit quartz combustion chamber and a conical convergent exit quartz combustion chamber, designed to provide a more representative geometric and acoustic boundary at the combustor outlet. Two inlet geometric swirl numbers of industrial relevance are chosen; namely 0.5 and 0.8. Combustion stability and heat release locations of lean premixed CH4-air and CH4-H2-air combustion are evaluated by a combination of OH planar laser induced fluorescence, OH* chemiluminescence, and dynamic pressure measurements. Changes in flame stabilization location are characterized by the use of an OH* chemiluminescence intensity centroid. Notable upstream flame movement coupled with changes in acoustic response are evident, particularly near the lean operating limit as hydrogen blending shifts lean blowoff of methane flames to lower equivalence ratios with corresponding reduction in NOx emissions. The influence of increased pressure on the lean operating point stability and emissions appear to be small over the range considered, however a power law correlation has been developed for scaling combustion noise amplitudes with inlet pressure and swirl number. Indicators of flame flashback as well as combustor acoustic response are affected considerably when the convergent combustor outlet geometry is deployed. This has been shown to alter the influence of the central recirculation zone as a flame stabilizing coherent flow structure. Chemical kinetic modelling supports the experimental observations that stable burner operation can be achieved with blended methane-hydrogen up to 15% by volume.

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Combustion of Hydrogen-Methane-Air-Mixtures in a Generic Triple Swirl Burner: Numerical Studies

10.1115/gt2021-59744 ◽

2021 ◽

Author(s):

Neha Vishnoi ◽

Agustin Valera-Medina ◽

Aditya Saurabh ◽

Lipika Kabiraj

Keyword(s):

Hydrogen Content ◽

Energy Demand ◽

Combustion Process ◽

Flow Fields ◽

Flame Stabilization ◽

Pollutant Emissions ◽

Temperature Fields ◽

Nox Emissions ◽

Swirl Burner ◽

High Hydrogen

Abstract Ever-increasing energy demand, limited non-renewable resources, requirement for increased operational flexibility, and the need for reduction of pollutant emissions are the critical factors that drive the development of next generation fuel flexible gas turbine combustors. The use of hydrogen and hydrogen-rich fuels such as syngas helps in achieving decarbonisation. However, high temperatures and flame speeds associated with hydrogen might increase the NOx emissions. Humidified combustion presents a promising approach for NOx control. Humidification inhibits the formation of NOx and also allows for operating on hydrogen and hydrogen-rich fuels. The challenge in the implementation of this technology is the combustor (burner) design, which must provide a stable combustion process at high hydrogen content and ultra-wet conditions. In the present work, we investigate the flow field and combustion characteristics of a generic triple swirl burner running on humidified and hydrogen enriched methane-air mixtures. The investigated burner consists of three co-axial co-rotating swirling passages: outer radial swirler stage, and two inner concentric axial swirler stages. Reynold’s Averaged Navier-Stokes (RANS) simulation approach has been utilized here for flow description within the burner and inside the combustor. We present the flow fields from isothermal and lean pre-mixed methane-air reactive simulations based on the characterization of velocity profiles, streamwise shear layers, temperature fields and NOx emissions. Subsequently, we investigate the effect of combustion on flow fields, and flame stabilization for hydrogen enriched methane-air mixtures as a function of hydrogen content. We also investigate the effect of humidified combustion on methane-hydrogen blends and present comparison of temperature estimations and NOx emissions.

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Characterization of ALM Swirl Burner Surface Roughness and its Effects on Flame Stability Using High-Speed Diagnostics

Volume 4A: Combustion, Fuels, and Emissions ◽

10.1115/gt2019-90215 ◽

2019 ◽

Author(s):

Jon Runyon ◽

Anthony Giles ◽

Richard Marsh ◽

Daniel Pugh ◽

Burak Goktepe ◽

...

Keyword(s):

Surface Roughness ◽

Gas Turbine ◽

Gas Turbines ◽

High Speed ◽

Flame Stabilization ◽

Flame Stability ◽

Post Processing ◽

Swirl Burner ◽

Stability Limits ◽

Near Wall

Abstract The use of metallic Additive Layer Manufacturing (ALM) is an active area of development for gas turbine components, particularly concerning novel combustor prototypes for micro gas turbines. However, further study is required to understand the influence of this manufacturing technique and subsequent post-processing on the resulting burner component surface roughness and its effect on flame stability. In this study, two Inconel 625 swirl nozzle inserts with identical bulk geometry (swirl number, Sg = 0.8) were constructed via ALM for use in a generic gas turbine swirl burner. Further post-processing by grit blasting of one swirl nozzle insert results in a quantifiable change to the surface roughness characteristics in the burner exit nozzle when compared with the unprocessed ALM swirl nozzle insert or a third nozzle insert which has been manufactured using traditional machining methods. An evaluation of the influence of variable surface roughness effects from these swirl nozzle inserts is therefore performed under preheated isothermal and combustion conditions for premixed methane-air flames at thermal power of 25 kW. High-speed velocimetry at the swirler exit under isothermal air flow conditions gives evidence of the change in near-wall boundary layer thickness and turbulent fluctuations resulting from the change in nozzle surface roughness. Under atmospheric combustion conditions, this influence is further quantified using a combination of dynamic pressure, high-speed OH* chemiluminescence, and exhaust gas emissions measurements to evaluate the flame stabilization mechanisms at the lean blowoff and rich stability limits. Notable differences in flame stabilization are evident as the surface roughness is varied, and changes in rich stability limit were investigated in relation to changes in the near-wall turbulence intensity. Results show the viability of using ALM swirl nozzles in lean premixed gas turbine combustion. Furthermore, precise control of in-process or post-process surface roughness of wetted surfaces can positively influence burner stability limits and must therefore be carefully considered in the ALM burner design process as well as CFD models.

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Flame interactions in a stratified swirl burner: Flame stabilization, combustion instabilities and beating oscillations

Combustion and Flame ◽

10.1016/j.combustflame.2019.11.020 ◽

2020 ◽

Vol 212 ◽

pp. 500-509 ◽

Cited By ~ 5

Author(s):

Xiao Han ◽

Davide Laera ◽

Dong Yang ◽

Chi Zhang ◽

Jianchen Wang ◽

...

Keyword(s):

Flame Stabilization ◽

Combustion Instabilities ◽

Swirl Burner ◽

Burner Flame

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Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner with Central Bluff Body

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4048977 ◽

2020 ◽

Author(s):

Fernando Biagioli ◽

Alessandro Innocenti ◽

Steffen Terhaar ◽

Teresa Marchione

Keyword(s):

Numerical Analysis ◽

Bluff Body ◽

Reverse Flow ◽

Flame Stabilization ◽

Turbulent Flames ◽

Experimental Investigations ◽

Swirl Burner ◽

Stable Flame ◽

Sudden Transition ◽

Flame Behaviour

Abstract Lean premixed gas turbulent flames stabilized in the flow generated by an industrial swirl burner with a central bluff body are experimentally found to behave bi-stable. This bi-stable behaviour, which can be triggered via a small change in some of the controlling parameters, for example the bulk equivalence ratio, consists in a rather sudden transition of the flame from completely lifted to well attached to the bluff body. While several experimental investigations exist on this topic, numerical analysis is limited. The present work is therefore also of numerical nature, with a two-fold scope: a) simulation and validation with experiments of the bi-stable flame behaviour via Computational Fluid Dynamics (CFD) in the form of Large Eddy Simulation (LES) and b) analysis of CFD results to shed light on the flame stabilization properties. LES results, in case of the lifted flame, show that the vortex core is sharply precessing at a given frequency. Phase averaging these results at the frequency of precession clearly indicates a counter-intuitive and unexpected presence of reverse flow going all the way through the flame apex and the bluff body tip. A simple one-dimensional flame stabilization model is applied to explain the bi-stable flame behaviour.

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Effects of CO2 Dilution on Flame Stabilization and NOx Emission in a Small Swirl Burner and Furnace

Journal of Polytechnic ◽

10.2339/politeknik.1026159 ◽

2021 ◽

Author(s):

Mustafa İLBAŞ ◽

Göktürk CANDAN

Keyword(s):

Flame Stabilization ◽

Nox Emission ◽

Swirl Burner

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Experimental and Numerical Analysis of Gas Premix Turbulent Flames Stabilized in a Swirl Burner With Central Bluff Body

Volume 4A: Combustion, Fuels, and Emissions ◽

10.1115/gt2020-14243 ◽

2020 ◽

Author(s):

Fernando Biagioli ◽

Alessandro Innocenti ◽

Steffen Terhaar ◽

Teresa Marchione

Keyword(s):

Numerical Analysis ◽

Burning Rate ◽

Axial Velocity ◽

Bluff Body ◽

Reverse Flow ◽

Flame Stabilization ◽

Turbulent Flames ◽

Swirl Burner ◽

Lifted Flame ◽

Flame Behaviour

Abstract Lean premixed gas turbulent flames stabilized in the flow generated by an industrial swirl burner with a central bluff body are experimentally found to behave bi-stable. This bi-stable behaviour, which can be triggered via a small change in some of the controlling parameters, for example the bulk equivalence ratio, consists in a rather sudden transition of the flame from completely lifted to well attached to the bluff body. This has impact on combustion dynamics, emissions and pressure losses. While several experimental investigations exist on this topic, numerical analysis is limited. The present work is therefore also of numerical nature, with a two-fold scope: a) simulation and validation with experiments of the bi-stable flame behaviour via Computational Fluid Dynamics (CFD) in the form of Large Eddy Simulation (LES) and b) analysis of CFD results to shed light on the flame stabilization properties. LES results, in case of the lifted flame, show that the vortex core is sharply precessing at a given frequency. Phase averaging these results at the frequency of precession clearly indicates a counter-intuitive and unexpected presence of reverse flow going all the way through the flame apex and the bluff body tip. The counter-intuitive presence of a lifted flame is explained here in terms of the phase averaged data which show that the flame apex is not placed at the centre of the spinning reverse flow region. It is instead slightly shifted radially outward where the axial velocity recovers to low positive values of the order of the turbulent burning rate. A simple one-dimensional flame stabilization model is applied to explain this peculiar flame behaviour. This model provides first an estimation of the flame radius of curvature in terms of axial velocity and turbulence quantities. This radius is therefore used to determine the total flux of reactants into the flame, given by an axial convection and a radial diffusion contributions. Subsequently the possibility of the flame positioned at the centre of the vortex is excluded based on the balance between this flux and the turbulent burning rate. A clear explanation of the mechanism leading to the sudden flame jump has instead not been identified and only some hypotheses are provided.

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LES Combustion Model With Stretch and Heat Loss Effects for Prediction of Premix Flame Characteristics and Dynamics

Volume 4A: Combustion, Fuels and Emissions ◽

10.1115/gt2017-63357 ◽

2017 ◽

Cited By ~ 2

Author(s):

Luis Tay-Wo-Chong ◽

Alessandro Scarpato ◽

Wolfgang Polifke

Keyword(s):

Flow Field ◽

Heat Loss ◽

Turbulent Combustion ◽

Flame Stabilization ◽

Combustion Model ◽

Swirl Burner ◽

Combustion Models ◽

Variable Approach ◽

Large Eddy ◽

Good Agreement

The present paper extends an approach to include effects of stretch and heat losses into turbulent combustion models from the RANS framework to the LES framework. This approach has shown the potential to improve the prediction of flame stabilization by considering these combined effects. The model is based on the calculation of the consumption speed of laminar premixed flames influenced by variations in strain and heat loss in asymmetric counterflow configurations. The consumption speed depending on strain and heat loss is introduced into a turbulent combustion model based on a progress variable approach. Large Eddy Simulations of a fully-premixed axial swirl burner with and without the influence of stretch and heat loss effects are carried out and validated against flow field and OH* chemiluminescence measurements for different power ratings and equivalence ratios. Flame dynamics are also investigated by extracting the Flame Transfer Function of the fully-premixed axial swirl burner with System Identification methods. Good agreement on the flow field, flame characteristics and dynamics between experiment and simulation was obtained with the inclusion of stretch and heat loss effects into the combustion model. Results show the importance of including these effects into turbulence combustion models for the design of premix burners for gas turbine combustors.

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