Determination of Equivalence Ratio and Oscillatory Heat Release Distributions in Non-Premixed Bluff Body-Stabilized Flames Using Chemiluminescence Imaging

2011 ◽  
Author(s):  
Caleb Cross ◽  
Eugene Lubarsky ◽  
Dmitriy Shcherbik ◽  
Keary Bonner ◽  
Alex Klusmeyer ◽  
...  
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
Equivalence Ratio ◽  
Bluff Body ◽  
Fuel Injection ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Flame Holder ◽  
Air Stream ◽  
Local Equivalence

In an effort to elucidate the fundamental processes controlling bluff body flame stabilization, the dependence of the spatial distribution of the local equivalence ratio and the heat release dynamics upon the mode of fuel injection was studied. Experiments were performed in a single flame holder combustion channel which was supplied with a high-temperature air stream. Jet-A fuel was injected across the incoming air stream from one of two locations: a cylindrical fuel bar installed 0.25 m upstream of the bluff body, or from fuel injectors integrated within the bluff body 2.5 cm upstream of the trailing edge (i.e., close-coupled injection). The time-averaged spatial distributions of the combustion heat release were characterized by CH* and C2* chemiluminescence imaging of the flame, and ratios of the C2* to CH* light emission were used to characterize the local equivalence ratio. The spatial average of the C2*/CH* value in the flame was found to increase linearly with increasing global equivalence ratio for fuel injection upstream of the bluff body, whereas this value was relatively constant for close-coupled injection. This constant value equaled the same average C2*/CH* value obtained for upstream fuel injection at globally stoichiometric conditions, suggesting that combustion resulting from close-coupled fuel injection took place, on average, in stoichiometric flamelets throughout the combustor. The heat release dynamics due to asymmetric (von Ka´rma´n) vortex shedding were also investigated for each operating condition by recording high-speed movies of the flame at 24 kHz. Upon processing of these movies, the amplitudes of heat release fluctuations due to von Ka´rma´n vortex shedding were found to be significantly higher for close-coupled injection than for injection well upstream of the flame holder for all operating conditions. This is attributed to an increase in span-wise fuel-air mixing and near-wake heat release for upstream fuel injection, resulting in a hotter recirculation zone which suppressed the von Ka´rma´n instability more than the close-coupled case.

Dynamics of Non-Premixed Bluff Body-Stabilized Flames in Heated Air Flow

2010 ◽  
Author(s):  
Caleb Cross ◽  
Aimee Fricker ◽  
Dmitriy Shcherbik ◽  
Eugene Lubarsky ◽  
Ben T. Zinn ◽  
...  
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
High Speed ◽  
Bluff Body ◽  
Combustion Process ◽  
Flame Stabilization ◽  
Inlet Temperature ◽  
Fuel Injectors ◽  
Flame Holder ◽  
Process Heat

This paper describes a study of the fundamental flame dynamic processes that control bluff body-stabilized combustion of liquid fuel with low dilatation. Specifically, flame oscillations due to asymmetric vortex shedding downstream of a bluff body (i.e., the Be´nard/von-Ka´rma´n vortex street) were characterized in an effort to identify the fundamental processes that most affect the intensity of these oscillations. For this purpose, the spatial and temporal distributions of the combustion process heat release were characterized over a range of inlet velocities, temperatures, and overall fuel-air ratios in a single flame holder combustion channel with full optical access to the flame. A stream of hot preheated air was supplied to the bluff body using a preburner, and Jet-A fuel was injected across the heated gas stream from discrete fuel injectors integrated within the bluff body. The relative amplitudes, frequencies, and phase of the sinusoidal flame oscillations were characterized by Fourier analysis of high-speed movies of the flame. The amplitudes of the flame oscillations were generally found to increase with global equivalence ratio, reaching a maximum just before rich blowout. Comparison of the flame dynamics to the time-averaged spatial heat release distribution revealed that the intensity of the vortex shedding decreased as a larger fraction of the combustion process heat release occurred in the shear layers surrounding the recirculation zone of the bluff body. Furthermore, a complete transition of the vortex shedding and consequent flame stabilization from asymmetric to symmetric modes was clearly observed when the inlet temperature was reduced from 850°C to 400°C (and hence, significantly increasing the flame dilatation ratio from Tb/Tu ∼ 2.3 to 3.7).

Dynamics of Flame Stabilized by Triangular Bluff Body in Partially Premixed Methane-Air Combustion

2011 ◽  
Author(s):  
T. V. Santosh Kumar ◽  
P. R. Alemela ◽  
J. B. W. Kok
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Reaction Rates ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Partially Premixed Combustion ◽  
Computational Fluid Dynamics Analysis ◽  
Partially Premixed

In the design and operational tuning of gas turbine combustors it is important to be able to predict the interaction of the flame stabilization recirculation area with the burner aerodynamics. In the present paper transient computational fluid dynamics analysis is used to study these effects. Vortex interactions with the flame play a key role in many practical combustion systems. The interactions drive a large class of combustion instabilities and are responsible for changing the reaction rates, shape of the flame and the global heat release rate. The evolution of vortex shedding in reactive flows and its effects on the dynamics of the flame are important to be predicted. The present study describes dynamics of bluff body stabilized flames in a partially premixed combustion system. The bluff body is an equilateral wedge that induces the flame recirculation zone. The wedge is positioned at one-third length of the duct, which, is acoustically closed at the bottom end and open at the top. Transient computational modeling of partially premixed combustion is carried out using the commercial ANSYS CFX code and the results show that the vortex shedding has a destabilizing effect on the combustion process. Scale Adaptive Simulation turbulence model is used to compare between non-reacting cases and combustion flows to show the effects of aerodynamics-combustion coupling. The transient data reveals that frequency peaks of pressure and temperature spectra and is consistent with the longitudinal natural frequencies and Kelvin-Helmholtz instability frequency for reactive flow simulations. The same phenomenon is observed at different operating conditions of varying power. It has also been shown that the pressure and heat release are in phase, satisfying the Rayleigh criterion and therefore indicating the presence of aerodynamic-combustion instability. The data are compared to the scarce data on experiments and simulations available in literature.

Characteristics of Flame Bases for V-Gutters Stabilized Premixed Flames

2013 ◽  
Author(s):  
Fan Gong ◽  
Yong Huang
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Heat Conducting ◽  
Inlet Velocity ◽  
The Impact

The objective of this work is to investigate the flame stabilization mechanism and the impact of the operating conditions on the characteristics of the steady, lean premixed flames. It’s well known that the flame base is very important to the existence of a flame, such as the flame after a V-gutter, which is typically used in ramjet and turbojet or turbofan afterburners and laboratory experiments. We performed two-dimensional simulations of turbulent premixed flames anchored downstream of the heat-conducting V-gutters in a confined passage for kerosene-air combustion. The flame bases are symmetrically located in the shear layers of the recirculation zone immediately after the V-gutter’s trailing edge. The effects of equivalence ratio of inlet mixture, inlet temperature, V-gutter’s thermal conductivity and inlet velocity on the flame base movements are investigated. When the equivalence ratio is raised, the flame base moves upstream slightly and the temperature gradient dT/dx near the flame base increases, so the flame base is strengthened. When the inlet temperature is raised, the flame base moves upstream very slightly, and near the flame base dT/dx increases and dT/dy decreases, so the flame base is strengthened. As the V-gutter’s thermal conductivity increases, the flame base moves downstream, and the temperature gradient dT/dx near the flame base decreases, so the flame base is weakened. When the inlet velocity is raised, the flame base moves upstream, and the convection heat loss with inlet mixture increases, so the flame base is weakened.

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.

Effect of Fuel Injection Timing Relative to Ignition Timing on the Natural-Gas Direct-Injection Combustion

2001 ◽  
Author(s):  
Zuohua Huang ◽  
Seiichi Shiga ◽  
Takamasa Ueda ◽  
Nobuhisa Jingu ◽  
Hisao Nakamura ◽  
...  
Keyword(s):  
Heat Release ◽  
Late Stage ◽  
Equivalence Ratio ◽  
Fuel Injection ◽  
Direct Injection ◽  
Injection Timing ◽  
Ignition Timing ◽  
Fuel Injection Timing ◽  
Initial Stage ◽  
Wide Range

Abstract Effect of fuel injection timing relative to ignition timing on natural gas direct-injection combustion was studied by using a rapid compression machine. The ignition timing was fixed at 80 ms from the compression start. When the injection timing was relatively earlier (injection start at 60 ms), the heat release pattern showed slower burn in the initial stage and faster burn in the late stage, which is similar to that of flame propagation of a premixed gas. In contrast to this, when the injection timing was relatively later (injection start at 75 ms), the heat release rate showed faster burn in the initial stage and slower burn in the late stage, which is similar to that of diesel combustion. The shortest duration was realized at the injection end timing of 80 ms (the same timing as the ignition timing) over the wide range of equivalence ratio. The degree of charge stratification and the intensity of turbulence generated by the fuel jet is considered to cause these behaviors. Earlier injection leads to longer duration of the initial combustion, whereas the later injection does longer duration of the late combustion. Earlier injection showed relatively lower CO emission while later injection produces relatively lower NOx emission. It was suggested that earlier injection leads to lower mixture stratification combustion and later injection leads to higher mixture stratification combustion. Combustion efficiency maintained high value over the wide range of equivalence ratio.

scholarly journals A Model for Bluff Body Flame Stabilization

1986 ◽  
Author(s):  
J. A. De Champlain ◽  
M. F. Bardon
Keyword(s):  
Experimental Data ◽  
Equivalence Ratio ◽  
Bluff Body ◽  
Laminar Flame ◽  
Flame Stabilization ◽  
Effect Of Temperature ◽  
Laminar Flame Speed ◽  
Tabular Form ◽  
Chemical Effects ◽  
Stirred Reactor

Previous work on bluff body stabilization mechanisms is reviewed, and existing models are categorized in tabular form, showing the underlying assumptions and resulting equations. Lacunae in existing models are discussed, particularly their reliance on characteristics such as laminar flame speed which is difficult to predict for the conditions encountered in turbojet afterburners. A model for bluff body flame stabilization is proposed based on the stirred reactor approach. In addition to the effect of temperature, pressure and geometry, it includes chemical effects such as vitiation and fuel-air equivalence ratio. Blow off velocities predicted by the model are compared to experimental data for various conditions.

Zero Dimensional Quasi-Predictive Thermodynamic Simulation for Establishing Initial Cylinder Conditions for CFD Simulation of Diesel Combustion

2015 ◽  
Author(s):  
Ryan A. Bandura ◽  
Timothy J. Jacobs
Keyword(s):  
Experimental Data ◽  
Heat Release ◽  
Cfd Simulation ◽  
Fuel Injection ◽  
Initial Conditions ◽  
Thermodynamic Simulation ◽  
Operating Conditions ◽  
Gas Composition ◽  
Gas Temperature ◽  
Rate Of Heat Release

Computational fluid dynamics (CFD) is now a ubiquitous computational tool for engine design and diagnosis. It is often necessary to provide well-known initial cycle conditions to commence the CFD computations. Such initial conditions can be provided by experimental data. To create an opportunity to computationally study engine conditions where experimental data are not available, a zero-dimensional quasi-predictive thermodynamic simulation is developed that uses well-established spray model to predict rate of heat release and calculated burned gas composition and temperature to predict nitric oxide (NO) concentration. This simulation could in turn be used in reverse to solve for initial cylinder conditions for a targeted NO concentration. This paper details the thermodynamic simulation for diesel engine operating conditions. The goal is to produce a code that is capable of predicting NO emissions as well as performance characteristics such as mean effective pressure (MEP) and brake specific fuel consumption (BSFC). The simulation uses general conservation of mass and energy approaches to model intake, compression, and exhaust. Rate of heat release prediction is based on an existing spray model to predict how fuel concentrations within the spray jet change with penetration. Rate of heat release provides predicted cylinder pressure, which is then validated against experimental pressure data under known operating conditions. An equilibrium mechanism is used to determine burned gas composition which, along with burned gas temperature, can be used for prediction of NO in the cylinder. NO is predicted using the extended Zeldovich mechanism. This mechanism is highly sensitive to temperature, and it is therefore important to accurately predict cylinder gas temperature to obtain correct NO values. Additionally, MEP and BSFC are determined. The simulation focuses on single fuel injection events, but insights are provided to expand the simulation to model multiple injection events.

scholarly journals Influence of Fuel Injection, Turbocharging and EGR Systems Control on Combustion Parameters in an Automotive Diesel Engine

2019 ◽  
Vol 9 (3) ◽  
pp. 484 ◽  
Author(s):  
Giorgio Zamboni
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Alternative Fuels ◽  
Fuel Injection ◽  
Combustion Process ◽  
Environmental Parameters ◽  
Operating Conditions ◽  
Combustion Noise ◽  
First Derivative ◽  
Test Sets

Indicated pressure diagrams were measured during experimental campaigns on the control of fuel injection, turbocharging and hybrid exhaust gas recirculation systems in an automotive downsized diesel engine. Three-part load operating conditions were selected for four test sets, where strategies aimed at the reduction of NOX emissions and fuel consumption, limiting penalties in soot emissions and combustion noise were applied to the selected systems. Processing of in-cylinder pressure signal, its first derivative and curves of the rate of heat release allowed us to evaluate seven parameters related to the combustion centre and duration, maximum values of pressure, heat release and its first derivative, heat released in the premixed phase and a combustion noise indicator. Relationships between these quantities and engine operating, energy and environmental parameters were then obtained by referring to the four test sets. In the paper, the most significant links are presented and discussed, aiming at a better understanding of the influence of control variables on the combustion process and the effects on engine behaviour. The proposed methodology proved to be a consistent tool for this analysis, useful for supporting the application of alternative fuels or advanced combustion modes.

CH*/OH* Chemiluminescence Response of an Atmospheric Premixed Flame Under Varying Operating Conditions

2010 ◽  
Author(s):  
Daniel Guyot ◽  
Felix Guethe ◽  
Bruno Schuermans ◽  
Arnaud Lacarelle ◽  
Christian Oliver Paschereit
Keyword(s):  
Equivalence Ratio ◽  
Fuel Injection ◽  
Wave Length ◽  
Optical Filters ◽  
Operating Conditions ◽  
Chemiluminescence Intensity ◽  
Ratio Distribution ◽  
Iccd Camera ◽  
Air Mass ◽  
Co2 Intensity

In this work the relationship between the ratio of the global CH* and OH* flame chemiluminescece and the global equivalence ratio of a technically premixed swirl-stabilized flame is investigated. The burner allows for a modification of the premix fuel injection pattern. The global flame chemiluminescence is monitored by a high-sensitivity light spectrometer and multiple photo-multipliers. The photo-multipliers were equipped with narrow optical band-pass filters and recorded the flame’s OH*, CH* and CO2* chemiluminescence intensity. To ensure an approximately uniform equivalence ratio distribution in the combustion zone, the spatial OH* and CH* flame chemiluminescence was recorded simultaneously with one ICCD camera using a special optical setup, which incorporated among other things one fully reflective and one semi-reflective mirror and appropriate optical filters. The flame chemiluminescence intensity was mapped for a range of equivalence ratios and air mass flows. The mapping shows that (as stated for perfectly premixed flames in the literature) the OH*, CH* and CO2* intensity of the investigated flame depends linearly on the air mass flow and exponentially on the equivalence ratio (i.e., I = km * φβ). Hence for the investigated operating conditions (i.e., quasi premix conditions) the global CH*/OH* intensity can be employed as a measure of the global equivalence ratio for the operating conditions investigated in this work. However, the contribution of broadband CO2* chemiluminescence in the wave length range of CH* chemiluminescence has to be accounted for.

The influence of the geometry of V-gutter bluff body on transient vortex shedding

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Luckachan K George ◽  
Raja Sekar K ◽  
Srikrishnan A R ◽  
Kannan R
Keyword(s):  
Vortex Shedding ◽  
High Speed ◽  
Bluff Body ◽  
Vortex Motion ◽  
Flame Stabilization ◽  
Cold Flow ◽  
Transient Simulations ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
The Impact

Abstract This study investigates the turbulent flow field downstream of V-gutters using unsteady numerical modelling. An important domain of application of the vortex shedding induced by the V-gutters is the flame stabilization in high speed combustion systems which find extensive applications in aerospace engineering. In view of this, the present study analyses the impact of the V-gutter geometry, as characterized by the included angle, on inducing vortex motion in the wake. Transient simulations are carried out for three values of the semi-span angle, α = 30°, 45° and 60°. Based on the analysis of the saddle point and the vortex shedding frequency, the study shows that an increase in span angle within this range, favours the effectiveness of the method in flame stabilization. Though the simulations are done for cold flow, the dominant mechanism of vortex shedding is adequately addressed in the analysis.

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