A Review of Mechanisms Controlling Bluff-Body Stabilized Flames With Closely-Coupled Fuel Injection

2011 ◽  
Author(s):  
Jeffery A. Lovett ◽  
Caleb Cross ◽  
Eugene Lubarsky ◽  
Ben T. Zinn
Keyword(s):  
Liquid Fuel ◽  
Bluff Body ◽  
Fuel Injection ◽  
Flame Structure ◽  
Flame Stabilization ◽  
Current Understanding ◽  
Two Phase ◽  
Combustion Region ◽  
Combustion Systems ◽  
And Performance

The processes controlling bluff-body stabilized combustion have been extensively studied over the years because such stabilization approaches are commonly used in many practical systems. Much of the current understanding of this problem was attained in experimental and analytical studies of premixed combustion systems where the complexities introduced by fuel atomization, vaporization and mixing could be neglected. Yet, practical considerations often require fuel injection just upstream of the bluff-body stabilized combustion region. Consequently, it’s necessary to develop understanding of the fundamental processes in such non-premixed systems. Supplying fuel via the injection of discrete liquid fuel jets requires understanding of the complex physics of two-phase sprays and the transport to various regions within the combustor. This paper describes current understanding of the manner in which these processes affect flame stabilization in bluff-body combustion systems that employ close-coupled, liquid fuel injection. Specifically, the paper compares findings of premixed bluff-body flames with recent results obtained in studies using close-coupled fueling at Georgia Tech to support postulates of the processes controlling flame stabilization and flame structure. These findings are also used to propose a set of parameters that can be used to describe the combustion behavior and performance of such combustion systems.

Effects of Pilot Fuel and Liner Cooling on the Flame Structure in a Full Scale Swirl-Stabilized Combustion Setup

2009 ◽  
Author(s):  
Jens Fa¨rber ◽  
Rainer Koch ◽  
Hans-Jo¨rg Bauer ◽  
Matthias Hase ◽  
Werner Krebs
Keyword(s):  
Combustion Chamber ◽  
Fuel Injection ◽  
Flame Structure ◽  
Cone Angle ◽  
Flow Patterns ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Combustion Noise ◽  
Pilot Fuel ◽  
Combustor Liner

The flame structure and the limits of operation of a lean premixed swirl flame were experimentally investigated under piloted and non-piloted conditions. Flame stabilization and blow out limits are discussed with respect to pilot fuel injection and combustor liner cooling for lean operating conditions. Two distinctly different flow patterns are found to develop depending on piloting and liner cooling parameters. These flow patterns are characterized with respect to flame stability, blow out limits, combustion noise and emissions. The combustion system explored consists of a single burner similar to the burners used in Siemens annular combustion systems. The burner feeds a distinctively non-adiabatic combustion chamber operated with natural gas under atmospheric pressure. Liner cooling is mimicked by purely convective cooling and an additional flow of ‘leakage air’ injected into the combustion chamber. Both, this additional air flow and the pilot fuel ratio were found to have a strong influence on the flow structure and stability of the flame close to the lean blow off limit (LBO). It is shown by Laser Doppler Velocimetry (LDV) that the angle of the swirl cone is strongly affected by pilot fuel injection. Two distinct types of flow patterns are observed close to LBO in this large scale setup: While non-piloted flames exhibit tight cone angles and small inner recirculation zones (IRZ), sufficient piloting results in a wide cone angle and a large IRZ. Only in the latter case, the main flow becomes attached to the combustor liner. Flame structures deduced from flow fields and CH-Chemiluminescence images depend on both the pilot fuel injection and liner cooling.

Combustion Characteristics and Performance Increase of an LPG-SI Engine with Liquid Fuel Injection System

2009 ◽  
Author(s):  
Norifumi Mizushima ◽  
Susumu Sato ◽  
Yasuhiro Ogawa ◽  
Toshiro Yamamoto ◽  
Umerujan Sawut ◽  
...  
Keyword(s):  
Liquid Fuel ◽  
Fuel Injection ◽  
Combustion Characteristics ◽  
Injection System ◽  
Fuel Injection System ◽  
Si Engine ◽  
And Performance

Combustion Characteristics of a Peripheral Vortex Reverse Flow Combustor With Coaxial Fuel Injection

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Raghav Sood ◽  
Preetam Sharma ◽  
Vaibhav Kumar Arghode
Keyword(s):  
Liquid Fuel ◽  
Fuel Injection ◽  
Reverse Flow ◽  
Flame Structure ◽  
Operating Conditions ◽  
Single Digit ◽  
Air Jet ◽  
Fuel Jet ◽  
Primary Breakup ◽  
Reaction Zones

Abstract This paper deals with an experimental investigation of a novel and simple reverse flow combustor, operated stably with a liquid fuel (ethanol) for heat release intensities ranging from 16 to 25 MW/(m3·atm) with very low NOx and CO emissions. The liquid fuel is injected coaxially with the air jet along the centerline of the combustor. The high velocity air annulus helps in primary breakup of the liquid fuel jet. Air injection along the combustor centerline results in a strong peripheral vortex inside the combustor leading to enhanced product gas recirculation, internal preheating of the reactants, and stabilization of reaction zones. Single-digit NOx emissions were obtained for both coaxial fuel injection (non-premixed) and a premixed–prevaporized (PP) cases for all operating conditions. CO emissions for both the modes were less than 100 ppm (ϕ < 0.75). CH* chemiluminescence images revealed two distinct flame structures for coaxial fuel injection case. A single flame structure for PP case was observed extending from the injector exit to the bottom of the combustor. The instantaneous (spatially averaged) CH* intensity fluctuations were significantly lower for the PP case as compared to the coaxial fuel injection case.

Experimental Investigation Into the Role of Mean Flame Stabilization On the Combustion Dynamics of High-Hydrogen Fuels in a Turbulent Combustor

2021 ◽  
Author(s):  
Nikhil Ashokbhai Baraiya ◽  
Vikram Ramanan ◽  
Baladandayuthapani Nagarajan ◽  
Chetankumar S Vegad ◽  
S. R. Chakravarthy
Keyword(s):  
Bluff Body ◽  
Flame Structure ◽  
High Amplitude ◽  
Acoustic Mode ◽  
Flame Stabilization ◽  
Pure Hydrogen ◽  
Airflow Rate ◽  
High Hydrogen ◽  
Combustion Dynamics

Abstract A bluff-body turbulent combustor is mapped for its thermo-acoustic stability across variation in airflow rate, non-dimensionalized as the Reynolds number (Re) and fuel composition. The combustor stability is evaluated for three fuels, namely, pure hydrogen (PH), synthesis natural gas (SNG), and syngas (SG). The combustion dynamics display markedly different behavior across the fuels, in the extent of the unstable region, as well as the observed dominant Eigenvalues. At low Re, SNG displays stable combustion, while SG exhibits high amplitude oscillations at the fundamental duct acoustic mode. As the Re is increased, SNG displays very high amplitude oscillations at the duct acoustic mode, while SG exhibit relatively low amplitude oscillations at the third harmonic. In the case of PH, high amplitude oscillations observed at higher Re at the first harmonic. These peculiarities are investigated in light of the role of mean flame stabilization. The combustion dynamics of fuels is influenced by the global equivalence ratio, as well as the jet momentum ratio. These effects significantly demarcates the dynamics of SNG and SG combustion. This is seen manifested in mean flame structure of flame at high amplitude oscillations, whereby result in SNG flame to be present in the wake, while the SG flame resides in the shear layer. The driving by the flame because of their mean stabilization quantified by a spatial Rayleigh index. It confirms the presence of large driving regions for SNG compared to that of SG, results in the observed differences in amplitude of the oscillations.

Towards a Detailed Liquid Fuel Injection Model for Gas Turbine Combustor CFD

2020 ◽  
Author(s):  
L. Wang ◽  
H. Ozogul ◽  
T. Kaushik ◽  
A. Bhat ◽  
S. Rida
Keyword(s):  
Boundary Condition ◽  
Liquid Fuel ◽  
Fuel Injection ◽  
Initial Conditions ◽  
Model Performance ◽  
Fuel Spray ◽  
Two Phase ◽  
Lagrangian Simulation ◽  
Fine Mesh ◽  
Injection Model

Abstract Fuel injection modeling plays an important role in Computational Fluid Dynamics (CFD) based combustor design and performance analysis. The specification of initial fuel spray size, velocity, and location strongly affects the subsequent fuel air mixing and combustion processes. Current common practice of introducing fuel spray in combustor CFD relies on either experimental correlations built from spray data measured at locations further away from injector exit or simplified theoretical models that have limited applications. This often leads to large uncertainties in spray initial conditions and inconsistencies in combustor model performance. Although much progress has been made in multiphase simulation of primary atomization, involving a two-phase flow solver in combustor CFD to resolve liquid fuel injection processes is still not feasible in the foreseeable future. Standalone fuel injection simulations, however, can provide valuable information on initial spray distributions required for accurate fuel injection modeling in combustor CFD. In this paper the approach of using a standalone or separate detailed fuel injection simulation to provide initial spray boundary condition for combustor CFD is demonstrated in a Liquid Jet In Cross Flow (LJICF) configuration. The primary atomization (PA) of the LJICF is simulated using a Volume of Fluid (VOF) solver on a fine mesh, and the blobs and ligaments from the PA simulation are collected and transferred to another separate simulation of spray using a Lagrangian particle tracking solver on a coarser mesh. The results from the Lagrangian simulation are compared with experimental data as well as the results from a conventional fuel injection model. The differences from the comparisons are discussed to reveal the challenges and new modeling needs associated with this detailed fuel injection model. These include the effect of mesh resolution on the spray boundary condition, the need for blockage modeling, and the need for ligament breakup modeling.

scholarly journals A Comparison of the Characteristics of Planar and Axisymmetric Bluff-Body Combustors Operated under Stratified Inlet Mixture Conditions

2013 ◽  
Vol 2013 ◽  
pp. 1-15
Author(s):  
G. Paterakis ◽  
K. Souflas ◽  
E. Dogkas ◽  
P. Koutmos
Keyword(s):  
Large Scale ◽  
Cross Correlation ◽  
Bluff Body ◽  
Fuel Injection ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Control Measures ◽  
Effective Control ◽  
Large Eddy ◽  
Flame Region

The work presents comparisons of the flame stabilization characteristics of axisymmetric disk and 2D slender bluff-body burner configurations, operating with inlet mixture stratification, under ultralean conditions. A double cavity propane air premixer formed along three concentric disks, supplied with a radial equivalence ratio gradient the afterbody disk recirculation, where the first flame configuration is stabilized. Planar fuel injection along the center plane of theleading faceof a slender square cylinder against the approach cross-flow results in a stratified flame configuration stabilized alongside the wake formation region in the second setup. Measurements of velocities, temperatures,OH∗andCH∗chemiluminescence, local extinction criteria, and large-eddy simulations are employed to examine a range of ultralean and close to extinction flame conditions. The variations of the reacting front disposition within these diverse reacting wake topologies, the effect of the successive suppression of heat release on the near flame region characteristics, and the reemergence of large-scale vortical activity on approach to lean blowoff (LBO) are investigated. The cross-correlation of the performance of these two popular flame holders that are at the opposite ends of current applications might offer helpful insights into more effective control measures for expanding the operational margin of a wider range of stabilization configurations.

On the Influence of Fuel Distribution on the Flame Structure of Bluff-Body Stabilized Flames

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Jeffery A. Lovett ◽  
Kareem Ahmed ◽  
Oleksandr Bibik ◽  
Andrew G. Smith ◽  
Eugene Lubarsky ◽  
...  
Keyword(s):  
Reaction Zone ◽  
Bluff Body ◽  
Fuel Injection ◽  
Flame Structure ◽  
Reacting Flow ◽  
Oh Radicals ◽  
Fuel Distribution ◽  
Jet In Crossflow ◽  
Wide Range ◽  
Stabilized Flames

This paper describes recent learning on the flame structure associated with bluff-body stabilized flames and the influence of the fuel distribution with nonpremixed, jet-in-crossflow fuel injection. Recent experimental and analytical results disclosing the flame structure are discussed in relation to classical combustion reaction zone regimes. Chemiluminescence and planar fluorescence imaging of OH* radicals as an indicator of the flame zone are analyzed from various tests conducted at Georgia Tech using a two-dimensional vane-type bluff-body with simple wall-orifice fuel injectors. The results described in this paper support the view that combustion occurs in separated flame zones aligned with the nonpremixed fuel distribution associated with the fuel jets that are very stable and contribute to flame stability at low fuel flow rates. The experimental data is also compared with computational reacting flow large-eddy simulations and interpreted in terms of the fundamental reaction zone regimes for premixed flames. For the conditions of the present experiment, the results indicate combustion occurs over a wide range of flame regimes including the broken reaction zone or separated flamelet regimes.

Effects of Pilot Fuel and Liner Cooling on the Flame Structure in a Full Scale Swirl-Stabilized Combustion Setup

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Jens Färber ◽  
Rainer Koch ◽  
Hans-Jörg Bauer ◽  
Matthias Hase ◽  
Werner Krebs
Keyword(s):  
Combustion Chamber ◽  
Fuel Injection ◽  
Flame Structure ◽  
Cone Angle ◽  
Flow Patterns ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Combustion Noise ◽  
Pilot Fuel ◽  
Combustor Liner

The flame structure and the limits of operation of a lean premixed swirl flame were experimentally investigated under piloted and nonpiloted conditions. Flame stabilization and blow out limits are discussed with respect to pilot fuel injection and combustor liner cooling for lean operating conditions. Two distinctly different flow patterns are found to develop depending on piloting and liner cooling parameters. These flow patterns are characterized with respect to flame stability, blow out limits, combustion noise, and emissions. The combustion system explored consists of a single burner similar to the burners used in Siemens annular combustion systems. The burner feeds a distinctively nonadiabatic combustion chamber operated with natural gas under atmospheric pressure. Liner cooling is mimicked by purely convective cooling and an additional flow of “leakage air” injected into the combustion chamber. Both additional air flow and the pilot fuel ratio were found to have a strong influence on the flow structure and stability of the flame close to the lean blow off (LBO) limit. It is shown by laser Doppler velocimetry that the angle of the swirl cone is strongly affected by pilot fuel injection. Two distinct types of flow patterns are observed close to LBO in this large scale setup: While nonpiloted flames exhibit tight cone angles and small inner recirculation zones (IRZs), sufficient piloting results in a wide cone angle and a large IRZ. Only in the latter case, the main flow becomes attached to the combustor liner. Flame structures deduced from flow fields and CH-chemiluminescence images depend on both the pilot fuel injection and liner cooling.

Experimental Investigation on Lean Blow Out of a Piloted Aero-Engine Burner

2014 ◽  
Author(s):  
R. Bhagwan ◽  
J. C. Wollgarten ◽  
P. Habisreuther ◽  
N. Zarzalis
Keyword(s):  
Liquid Fuel ◽  
Laser Doppler Anemometry ◽  
Flame Structure ◽  
Field Measurements ◽  
Flame Stabilization ◽  
Nox Formation ◽  
Fuel Distribution ◽  
Lean Combustion ◽  
Aero Engine ◽  
Operational Range

One of the preferred ways to reduce NOX formation in an aero-engine is to operate lean throughout the whole operational range; however the lean combustion suffers from poor stability. To avoid the problem associated with stability, often a rich pilot flame is used along with a main flame to act as a source of heat and radicals to the main flame. The focus of the paper is to discuss the influence of the liquid fuel spray characteristics and effect of flow parameters on the lean blow out (LBO) limits of a piloted burner. In order to understand the observed remarkable LBO limits of the pilot flame with Jet A-1 (LBO = 145 kg-air to kg-fuel at 0.1 MPa of combustor pressure), velocity field measurements by laser Doppler Anemometry (LDA) technique have been performed. Furthermore, the flame structure has been analyzed with OH* chemiluminescence imaging. Experimental results show that the LBO limits of the burner running with liquid fuel further improves with an increase in combustor pressure. Such improvement in LBO limits is attributed to the change in the liquid fuel distribution caused by the change in the combustor pressure. For gaseous fuel measurements, results indicate that the equivalence ratio and the momentum ratio of the pilot jet to the co-annular flow are the dominating parameters that control the mixing process in the combustor and the ensuing effect on the flame structure and location of flame stabilization is substantial. The flame stabilizes either along the centreline or along the shear layer between two jets. Such information is useful in designing a lean partially premixed combustion system where a pilot flame is required to stabilize a main lean flame.

Large Eddy Simulation of Swirling Kerosene/Air Spray Flame Using Tabulated Chemistry

2013 ◽  
Author(s):  
B. Franzelli ◽  
A. Vié ◽  
B. Fiorina ◽  
N. Darabiha
Keyword(s):  
Large Eddy Simulation ◽  
Flame Structure ◽  
Flame Stabilization ◽  
Injection System ◽  
Two Phase ◽  
Detailed Chemistry ◽  
Eddy Simulation ◽  
Spray Flame ◽  
Tabulated Chemistry ◽  
Large Eddy

Accurate characterization of swirled flames is a key point in the development of more efficient and safer aeronautical engines. The task is even more challenging for spray injection systems. On the one side, spray interacts with both turbulence and flame, eventually affecting the flame dynamics. On the other side, spray flame structure is highly complex due to equivalence ratio inhomogeneities caused by the evaporation process. Introducing detailed chemistry in numerical simulations, necessary for the prediction of flame stabilization, ignition and pollutant concentration, is then essential but extremely expensive in terms of CPU time. In this context, tabulated chemistry methods, expressly developed to account for detailed chemistry at a reduced computational cost in Large Eddy Simulation of turbulent gaseous flames, are attractive. The objective of this work is to propose a first computation of a swirled spray flame stabilized in an actual turbojet injection system using tabulated chemistry. A Large Eddy Simulation of an experimental benchmark, representative of an industrial swirl two-phase air/kerosene injection system, is performed using a standard tabulated chemistry method. The numerical results are compared to the experimental database in terms of mean and fluctuating axial velocity. The reactive two-phase flow is deeper investigated focusing on the flame structure and dynamics.

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