Research on the flame structure characteristics and NOx pathways of low swirl combustion

2021 ◽  
pp. 095441002110161
Author(s):  
Zhibo Cao ◽  
Yinli Xiao ◽  
Xin Ming ◽  
Wenyan Song
Keyword(s):  
Flow Field ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Flame Structure ◽  
Chemical Reactor ◽  
Flame Zone ◽  
Structure Characteristics ◽  
Swirl Combustion ◽  
Dynamics Simulations ◽  
Reactor Network

Low swirl combustion (LSC) technology has the advantage of ultralow NOx emissions, which is of great significance to the development of low-emission gas turbine engines in the future. To investigate the flow field and flame structure characteristics of LSC, a test rig of low swirl burner was designed and developed. Particle image velocimetry measurement results show that the location and size of the recirculation zone are different, and the flow field shows typical “W”- and “U”-shaped distributions under various swirling flow conditions. The self-luminous results of LSC show that there are three flame modes including attached flame, “W”-shaped flame, and “U”-shaped flame. To deeply understand NOx generation pathways, a chemical reactor network model was developed based on experiments and computational fluid dynamics simulations, and the effects of premixed gas components on NOx pathways were calculated by using Chemkin software. It was verified that the NOx production of the CH4 mixture mixed with H2, N2, and CO2 was mainly formed by the thermal NO pathway in the recirculation zone. The increase of H2 promotes the generation of NNH-type NOx in the main flame zone and inhibits prompt NOx. The addition of N2 and CO2 greatly promotes the generation of prompt NOx and at the same time inhibits NNH-type NOx. In addition, there is little prompt NOx formation in the post-flame zone.

scholarly journals Non-premixed swirl-type tubular flames burning liquid fuels

2018 ◽  
Vol 846 ◽  
pp. 210-239
Author(s):  
Vinicius M. Sauer ◽  
Fernando F. Fachini ◽  
Derek Dunn-Rankin
Keyword(s):  
Flow Field ◽  
Swirling Flow ◽  
Flame Structure ◽  
Flow Analysis ◽  
Liquid Fuels ◽  
Reacting Flow ◽  
Surface Mass ◽  
Surface Mass Transfer ◽  
Incompressible Viscous Flow ◽  
Porous Walls

Tubular flames represent a canonical combustion configuration that can simplify reacting flow analysis and also be employed in practical power generation systems. In this paper, a theoretical model for non-premixed tubular flames, with delivery of liquid fuel through porous walls into a swirling flow field, is presented. Perturbation theory is used to analyse this new tubular flame configuration, which is the non-premixed equivalent to a premixed swirl-type tubular burner – following the original classification of premixed tubular systems into swirl and counterflow types. The incompressible viscous flow field is modelled with an axisymmetric similarity solution. Axial decay of the initial swirl velocity and surface mass transfer from the porous walls are considered through the superposition of laminar swirling flow on a Berman flow with uniform mass injection in a straight pipe. The flame structure is obtained assuming infinitely fast conversion of reactants into products and unity Lewis numbers, allowing the application of the Shvab–Zel’dovich coupling function approach.

Significant of Isothermal Flow Studies for High Swirling Flow in Unconfined Burner

2015 ◽  
Vol 789-790 ◽  
pp. 477-483
Author(s):  
A.R. Norwazan ◽  
M.N. Mohd Jaafar
Keyword(s):  
Flow Field ◽  
Combustion Chamber ◽  
Turbulent Flows ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Numerical Study ◽  
Tangential Velocity ◽  
Radial Distance ◽  
Navier Stokes ◽  
Reacting Flow

This paper is presents numerical simulation of isothermal swirling turbulent flows in a combustion chamber of an unconfined burner. Isothermal flows of with three different swirl numbers, SN of axial swirler are considered to demonstrate the effect of flow axial velocity and tangential velocity to define the center recirculation zone. The swirler is used in the burner that significantly influences the flow pattern inside the combustion chamber. The inlet velocity, U0 is 30 m/s entering into the burner through the axial swirler that represents a high Reynolds number, Re to evaluate the differences of SN. The significance of center recirculation zone investigation affected by differences Re also has been carried out in order to define a good mixing of air and fuel. A numerical study of non-reacting flow into the burner region is performed using ANSYS Fluent. The Reynolds–Averaged Navier–Stokes (RANS) realizable k-ε turbulence approach method was applied with the eddy dissipation model. An attention is focused in the flow field behind the axial swirler downstream that determined by transverse flow field at different radial distance. The results of axial and tangential velocity were normalized with the U0. The velocity profiles’ behaviour are obviously changes after existing the swirler up to x/D = 0.3 plane. However, their flow patterns are similar for all SN after x/D = 0.3 plane towards the outlet of a burner.

The Effect of Velocity in High Swirling Flow in Unconfined Burner

2014 ◽  
Vol 69 (6) ◽  
Author(s):  
Norwazan A. R ◽  
Mohammad Nazri Mohd. Jaafar
Keyword(s):  
Flow Field ◽  
Turbulent Flows ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Numerical Study ◽  
Tangential Velocity ◽  
Reacting Flow ◽  
Ansys Fluent ◽  
Inlet Velocity ◽  
Burner Exit

This paper presents a numerical simulation of swirling turbulent flows in combustion chamber of unconfined burner. Isothermal flows with three different swirl numbers using axial swirler are used to demonstrate the effect of flow in axial velocity and tangential velocity on the center recirculation zone. The significance of center recirculation zone is to ensure a good mixing of air and fuel in order to get a better combustion. The inlet velocity, U0 is 30 m/s entering into the burner through the axial swirler that is represents a high Reynolds number. A numerical study of non-reacting flow in the burner region is performed using ANSYS Fluent. The Reynolds–Averaged Navier–Stokes (RANS) standard k-ε turbulence approach method was applied with the eddy dissipation model. The paper focuses the flow field behind the axial swirler downstream that determined by transverse flow field at different on radial distances. The results of axial and tangential velocity were normalized with the inlet velocity. The velocity profiles are different after undergoing the different swirler up to the burner exit. However, the results of velocity profile showed that the high SN gives a better swirling flow patterns. 

Effect of Dome Geometry on Swirling Flow Field Characteristics of a Counter-Rotating Radial-Radial Swirler

2013 ◽  
Author(s):  
Yi-Huan Kao ◽  
Samir B. Tambe ◽  
San-Mou Jeng
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Aerodynamic Characteristics ◽  
Sudden Expansion ◽  
Reacting Flow ◽  
Clockwise Rotation ◽  
Expansion Angle ◽  
Flow Field Characteristics

An experimental study has been conducted to study the effect of the dome geometry on the aerodynamic characteristics of a non-reacting flow field. The flow was generated by a counter-rotating radial-radial swirler consisting of an inner, primary swirler generating counter-clockwise rotation and an outer, secondary swirler generating clockwise rotation. The dome geometry was modified by introducing dome expansion angles of 60° and 45° with respect to the swirler centerline, in addition to the baseline case of sudden expansion (90°). The flow downstream of the swirler is confined by a 50.8mm × 50.8mm × 304.8mm (2″ × 2″ × 12″) plexiglass chamber. A two-component laser doppler velocimetry (LDV) system was used to measure the velocities in the flow field. The dome geometry is seen to have a clear impact on mean swirling flow structure near the swirler exit rather than the downstream flow field. For the configurations with 60° and 45° expansion, no corner recirculation zone is observed and the swirling flow structure is asymmetric due to the non-axisymmetric dome geometry. The cross-section area of central recirculation zone is larger for dome geometry with 60° expansion angle, as compared to the 90° and 45° cases. The configurations with 60° and 45° expansion have higher magnitudes of negative velocity inside the core of central recirculation zone, as compared to the configuration with 90° expansion angle.

Experimental Study on Flow Structure of Non-Premixed Swirl Burner Flows Using PIV

2011 ◽  
Vol 347-353 ◽  
pp. 2587-2592 ◽  
Author(s):  
Bing Ge ◽  
Shu Sheng Zang ◽  
Pei Qing Guo
Keyword(s):  
Flow Field ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Spatial Separation ◽  
Complex Flow ◽  
Image Velocimetry ◽  
Characteristic Modes ◽  
Swirling Flame ◽  
Development And Validation ◽  
Annular Jets

This paper focuses on investigating the characteristic modes and structures in non-premixed swirling methane/air flames. Using the Particle Image Velocimetry (PIV) technique, the experiment measured the velocity distributions of the swirling flame. Cold flow conditions have been included to provide a picture of the flow field and to demonstrate the modifications induced by combustion. The characteristic lengths, velocity vectors, streamlines, and velocity distributions are presented and discussed. The experiment shows that a large spatial separation at the exit between the central and swirling annular jets can expedite the formation of a recirculation zone. Complex flow structures are found in the recirculation zone. Moreover, the differences between cold swirling flow field and combustion swirling flow are analyzed at length. The data from this experiment is helpful for optimization of the non-premixed burner design, and can be established as benchmarks for the development and validation of combustion numerical simulations.

Large eddy simulation of the influence of synthetic inlet turbulence on a practical aeroengine combustor with counter-rotating swirler

2017 ◽  
Vol 233 (3) ◽  
pp. 978-990 ◽  
Author(s):  
Yu Zhou ◽  
Yuan Huang ◽  
Zhongqiang Mu
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Reverse Flow ◽  
Boundary Layer Transition ◽  
Wall Region ◽  
Inlet Condition ◽  
Eddy Simulation ◽  
Large Eddy

To study the influence of inlet turbulence on the prediction of flow structure in practical aeroengine combustor, large eddy simulation with dynamic Smagorinsky subgrid model is used to explore the complex unsteady flow field in a single burner of a typical aeroengine combustor with two-stage counter-rotating swirler. The complex geometric configuration including all film cooling holes is fully simulated without any conventional simplification in order to reduce the modeling errors. First, unsteady process that flow developing from static to statistically stationary state is fully simulated under laminar inlet condition to obtain a fundamental understanding of flow characteristics in the combustor. Afterwards, synthetic eddy method is utilized to generate a turbulent inlet condition so that a perturbation with about 5% turbulence intensity is superimposed to the inlet plane. Simulation result shows that for the laminar inflow case, flow separation occurs in the near-wall region of the diffusion section, inducing a boundary layer transition and consequently introducing turbulence with nonuniformity in space before the swirler. In contrast, synthesized inflow generated under turbulent inlet condition by synthetic eddy method is more spatially homogeneous. Time-averaged flow field inside the swirler cup reveals that turbulent inflow ultimately causes the swirling flow with higher rotating speed in central region and more uniform distribution along the circumferential direction. It also enhances the transverse jet flow from primary holes and reverse flow in the central recirculation zone, and makes streamlines corresponding to the recirculation vortices more symmetrical on central profile. Maximum recirculating velocity predicted in central recirculation zone is −27.65 m/s and −17.86 m/s in turbulent and laminar case respectively, and corresponding total pressure recovery coefficient is 96.03% and 96.81%.

scholarly journals Numerical study of bluff-body non-premixed flame structures using laminar flamelet model

2005 ◽  
Vol 219 (5) ◽  
pp. 361-370 ◽  
Author(s):  
M Hossain ◽  
W Malalasekera
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Flame Structure ◽  
Local Extinction ◽  
Flamelet Model ◽  
Neck Zone ◽  
Laminar Flamelet ◽  
Laminar Flamelet Model

A laminar flamelet model is applied for bluff-body stabilized flames to study the flow field, mixing pattern, and the flame structure at two different velocities. The k - ɛ turbulence model is applied for accounting the turbulence fluctuations. It is found that the recirculation zone dominates the near field, while the far field structure is similar to the jet flow. The intermediate neck zone is the intense mixing region. The computation shows that the fuel jet velocity has significant effect on the structure of the flow field, which in turn has significant effect on the combustion characteristics. The laminar flamelet model is found to be adequate for simulating the temperature and the flame composition inside the recirculation zone. The flamelet model has, however, failed to account for the local extinction in the neck zone. Possible limitation of the laminar flamelet model to predict the local extinction is discussed.

Flashback Propensity in Swirl Stabilized Burner With Syngas Fuels

2010 ◽  
Author(s):  
Bidhan Dam ◽  
Gilberto Corona ◽  
Ahsan Choudhuri
Keyword(s):  
Flow Field ◽  
Recirculation Zone ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Fuel Mixture ◽  
Stoichiometric Ratio ◽  
Swirl Number ◽  
Significant Phenomenon ◽  
Transient Velocity ◽  
Fuel Mixtures

In swirl stabilized burner, combustion induced vortex breakdown (CIVB) flashback is a significant phenomenon. This paper presents experimental measurements of CIVB flashback propensity for hydrogen (H2)-carbon monoxide (CO) flames. The effects of H2 concentration, and swirl number on the flashback propensity of H2-CO flames are discussed. For a given air mass flow rate, the stoichiometric ratio (%F) at which the CIVB flashback occurs decreases with the increase in H2 concentration in fuel mixtures. However it appears that near the CIVB flashback limit, the swirl strength plays a more dominating role over the H2 concentration in the fuel mixture. The flashback propensity decreases with the increase in swirl number. An analysis of the nonreacting flow field (Air 6 g/s) as well as reacting (CH4-Air and H2-CO-Air) flame near the CIVB transient velocity field was conducted. The analysis revealed that a complex vortex-chemistry interaction leading to vortex breakdown and flashback occurred. The vector flow field showed that the high swirling flow generates a more stabilized and wider recirculation zone. It also showed that the presence of H2 dictates the intensity of the flashback process.

A review on the applications of the chemical reactor network approach on the prediction of pollutant emissions

2020 ◽  
Vol 92 (4) ◽  
pp. 551-570
Author(s):  
Hamidreza Khodayari ◽  
Fathollah Ommi ◽  
Zoheir Saboohi
Keyword(s):  
Flow Field ◽  
Chemical Reactor ◽  
Pollutant Emissions ◽  
Network Approach ◽  
Content Type ◽  
Modeling Methods ◽  
Chemical Reactor Network ◽  
Field Modeling ◽  
Reactor Network ◽  
Homogeneous Regions

Purpose The purpose of this paper is to review the applications of the chemical reactor network (CRN) approach for modeling the combustion in gas turbine combustors and classify the CRN construction methods that have been frequently used by researchers. Design/methodology/approach This paper initiates with introducing the CRN approach as a practical tool for precisely predicting the species concentrations in the combustion process with lower computational costs. The structure of the CRN and its elements as the ideal reactors are reviewed in recent studies. Flow field modeling has been identified as the most important input for constructing the CRNs; thus, the flow field modeling methods have been extensively reviewed in previous studies. Network approach, component modeling approach and computational fluid dynamics (CFD), as the main flow field modeling methods, are investigated with a focus on the CRN applications. Then, the CRN construction approaches are reviewed and categorized based on extracting the flow field required data. Finally, the most used kinetics and CRN solvers are reviewed and reported in this paper. Findings It is concluded that the CRN approach can be a useful tool in the entire process of combustion chamber design. One-dimensional and quasi-dimensional methods of flow field modeling are used in the construction of the simple CRNs without detailed geometry data. This approach requires fewer requirements and is used in the initial combustor designing process. In recent years, using the CFD approach in the construction of CRNs has been increased. The flow field results of the CFD codes processed to create the homogeneous regions based on construction criteria. Over the past years, several practical algorithms have been proposed to automatically extract reactor networks from CFD results. These algorithms have been developed to identify homogeneous regions with a high resolution based on the splitting criteria. Originality/value This paper reviews the various flow modeling methods used in the construction of the CRNs, along with an overview of the studies carried out in this field. Also, the usual approaches for creating a CRN and the most significant achievements in this field are addressed in detail.

Large eddy simulation study of flow field characteristics of a combustor with two coaxial swirlers

2019 ◽  
Vol 234 (5) ◽  
pp. 625-642
Author(s):  
Qun Zhang ◽  
Peng Zhang ◽  
Shun-li Sun ◽  
Ya-heng Song ◽  
Yi-fei Li ◽  
...  
Keyword(s):  
Flow Field ◽  
Proper Orthogonal Decomposition ◽  
Vortex Core ◽  
Large Scale ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Orthogonal Decomposition ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Proper Orthogonal

The cold and reaction flow fields of a combustor with two coaxial swirlers are investigated by means of large eddy simulation. Effective data processing methods such as proper orthogonal decomposition and fast Fourier transform are employed for analysis. The complex flow phenomena such as swirling jet, shear layer, recirculation zone, and precession vortex core are observed and their characteristics are analyzed. The dynamics of the flame and its interactions with the complex swirling flows and large-scale eddies are characterized. The precession vortex core structures and its influences on the combustion process are emphatically explored. It is found that the outer shear layer produces spiral precession vortex core cantilever structures and the change of structural characteristics of the PVC determines the pressure pulsation frequency of the combustor. The results also indicate precession vortex core accelerates the mixing of unburned and burned mixture, leading to the ignition. The principal structures are studied by determining the highest energy modes via proper orthogonal decomposition. The modes are classified according to energy size. By means of proper orthogonal decomposition four-decomposition method, the vortexes of different energy and scales in swirling flow field are classified and analyzed in detail, the flow field is reconstructed, and the large-scale coherent structures and small energy flow structures are obtained. A spectral map of the turbulent kinetic energy density exhibits the −5/3 slope given by the Kolmogorov–Obukhov law. Based on the analysis of the vortex structures and their evolution, and the analysis of the transports and distributions of flow field characteristic parameters, a novel unsteady swirling flow combustion organization mechanism is proposed. It is found that combustion mainly occurs in low-energy small-scale vortexes, releasing a large amount of heat. High-temperature gas enters the recirculation zone and continues to provide energy for the precession vortex cores.

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