The Effects of Fuel Composition on Flame Structure and Combustion Dynamics in a Lean Premixed Combustor

2007 ◽  
Author(s):  
Lorenzo Figura ◽  
Jong Guen Lee ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Fuel Composition ◽  
Two Dimensional ◽  
Inlet Velocity ◽  
Unstable Combustion ◽  
Fuel Mixtures

The stability characteristics of a laboratory-scale lean premixed combustor operating on natural gas - hydrogen fuel mixtures have been studied in a variable length combustor facility. The fuel and air were mixed upstream of the choked inlet to the combustor to eliminate equivalence ratio fluctuations and thereby ensure that the dominant instability driving mechanism was flame-vortex interaction. The inlet velocity, inlet temperature, equivalence ratio and percent hydrogen in the fuel were systematically varied, and at each operating condition the combustor pressure fluctuations were measured as a function of the combustor length. The results are presented in the form of two-dimensional stability maps, which are plots of the normalized rms pressure fluctuation versus the equivalence ratio and the combustor length, for a given inlet temperature, inlet velocity, and fuel mixture. In order to understand the effects of operating conditions and fuel composition on the observed stability characteristics, two-dimensional chemiluminescence images of the flame structure were recorded at all operating conditions and for all fuel mixtures under stable conditions. Changes in the stable flame structure, as characterized by the location of the flame’s “center of heat release”, were found to be consistent with the observed instability characteristics. The location of the flame’s “center of heat release” was found to lie along a single path for all operating conditions and fuel mixtures. It was also observed that there were regions of stable and unstable combustion as one moved along this path. Furthermore it was found that flames having the same “center of heat release” location, but different operating conditions and fuel composition, have very nearly the same flame shape. These results will be useful for developing phenomenological models for predicting unstable combustion.

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.

Experimental Investigation of Dual-Swirl Spray Flame in a Fuel Staged Optical Model Combustor With Laser Diagnostics

2021 ◽  
Author(s):  
Siheng Yang ◽  
Jianchen Wang ◽  
Zhichao Wang ◽  
Meng Han ◽  
Yuzhen Lin ◽  
...  
Keyword(s):  
Heat Release ◽  
Shear Layer ◽  
Optical Model ◽  
Flame Structure ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Main Stage ◽  
Staged Combustion ◽  
Swirl Number ◽  
Fuel Distribution

Abstract Lean premixed prevaporized combustors often feature staged combustion with a premixed main flame anchored by the nonpremixed pilot flame to obtain a wide operating range. Interaction between pilot flame and main flame is complex. The present article investigates the flame topologies and flame-fuel interactions in separated stratified swirl flames under various operating conditions (fuel to air ratio FAR and fuel stage ratio α) and injector designs (main stage swirl number Sm and fuel injection angle JA). Experiments are carried out in the centrally staged optical model combustor at inlet pressure P3 = 0.49–0.7 MPa and inlet temperature T3 = 539 K. At first, the flame structures obtained from OH-PLIF are investigated and discussed for the baseline injector (Sm = 0.9, JA = −50°). The V-shaped flame is stabilized in the inner shear layer (ISL) with the flame attachment point located at the lip for the pilot flame mode (α = 1). Dual flame is observed in the combustor for the fuel staged combustion (α < 1): the main flame stabilized in the outer shear layer (OSL) and the pilot flame stabilized in the inner shear layer (ISL). For increasing α from 0.15 to 0.25, gaps between the main flame and pilot flame are decreased, indicating a stronger interaction between the two flames. The flame structure for different injector geometries is then investigated. It is found that the higher main stage swirl number induces a larger flame opening angle, decreasing the interaction between two flames. Fuel injected into crossflow (JA = −50°) is found to generated a more separated flame, decreasing the flame interactions. Finally, fuel distribution measured by kerosene-PLIF is analyzed with the correlation to flame structure. Results show that the existence of a good mixing of fuel and fresh air in ISL and OSL provide favorable conditions for chemical reaction with high heat release. The OH distribution is highly correlated to fuel distribution. The fuel zone is located at the inner side of high OH region, indicating the reaction and heat release take place after the mixing of preheating of fuel-air mixture.

Effect of Pilot Flame on Flame Macrostructure and Combustion Instability

2017 ◽  
Author(s):  
Jihang Li ◽  
Stephen Peluso ◽  
Bryan Quay ◽  
Domenic Santavicca ◽  
James Blust ◽  
...  
Keyword(s):  
Dynamic Stability ◽  
Flame Structure ◽  
Three Dimensional ◽  
Inlet Temperature ◽  
Two Dimensional ◽  
Swirl Combustor ◽  
Pilot Fuel ◽  
Unstable Combustion ◽  
Stable Flame ◽  
The Stability

The effect of a pilot flame on the dynamic stability characteristics of a single-nozzle lean-premixed swirl combustor operating on natural gas fuel is investigated. Experiments are performed at a fixed inlet temperature and inlet velocity over a broad range of overall fuel-lean equivalence ratios with varied amounts of pilot fuel. The stability results are presented in the form of a dynamic stability map which is a three-dimensional graph of the normalized rms pressure fluctuation versus the overall equivalence ratio and percent pilot. The dynamic stability map identifies boundaries between stable and unstable combustion and results are presented characterizing the transition across one of these boundaries. Time-averaged two-dimensional chemiluminescence images of the stable flame and phase-averaged two-dimensional chemiluminescence images of the unstable flame are used to gain an understanding of the effect of the pilot on dynamic stability through changes in flame structure.

CFD Modeling of a Catalytic Flat Plate Fuel Reformer for Hydrogen Generation

2010 ◽  
Author(s):  
Kranthi K. Gadde ◽  
Panini K. Kolavennu ◽  
Susanta K. Das ◽  
K. J. Berry
Keyword(s):  
Flat Plate ◽  
Catalytic Combustion ◽  
Reaction Rates ◽  
Operating Conditions ◽  
Cfd Modeling ◽  
Design Parameters ◽  
Practical Implementation ◽  
Channel Height ◽  
Inlet Temperature ◽  
Two Dimensional

In this study, steam reforming of methane coupled with methane catalytic combustion in a catalytic plate reactor is studied using a two-dimensional mathematical model for co-current flow arrangement. A two-dimensional approach makes the model more realistic by increasing its capability to capture the effect of parameters such as catalyst thickness, reaction rates, inlet temperature and velocity, and channel height, and eliminates the uncertainties introduced by heat and mass transfer coefficients used in one-dimensional models. In our work, we simulate the entire flat plate reformer (both reforming side and combustion side) and carry out parametric studies related to channel height, inlet velocities, and catalyst layer thickness that can provide guidance for the practical implementation of such design. The operating conditions chosen make possible a comparison of the catalytic plate reactor and catalytic combustion analysis with the conventional steam reformer. The CFD results obtained in this study will be very helpful to understand the optimization of design parameters to build a first generation prototype.

Behavior Prediction Model in Gas Fueled Spark Ignition Internal Combustion Engines Turbocharged for Genset Application

2013 ◽  
Author(s):  
Jorge Duarte Forero ◽  
German Amador Diaz ◽  
Fabio Blanco Castillo ◽  
Lesme Corredor Martinez ◽  
Ricardo Vasquez Padilla
Keyword(s):  
Equivalence Ratio ◽  
Internal Combustion Engines ◽  
Combustion Engine ◽  
Internal Combustion ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Combustion Engines ◽  
Gaseous Fuels ◽  
Methane Number

In this paper, a mathematical model is performed in order to analyze the effect of the methane number (MN) on knock tendency when spark ignition internal combustion engine operate with gaseous fuels produced from different thermochemical processes. The model was validated with experimental data reported in literature and the results were satisfactory. A general correlation for estimating the autoignition time of gaseous fuels in function of cylinder temperature, and pressure, equivalence ratio and methane number of the fuel was carried out. Livengood and Wu correlation is used to predict autoignition in function of the crank angle. This criterium is a way to predict the autoignition tendency of a fuel/air mixture under engine conditions and consider the ignition delay. A chemical equilibrium model which considers 98 chemical species was used in this research in order to simulate the combustion of the gaseous fuels at differents engine operating conditions. The effect of spark advance, equivalence ratio, methane number (MN), charge (inlet pressure) and inlet temperature (manifold temperature) on engine knocking is evaluated. This work, explore the feasibility of using syngas with low methane number as fuel for commercial internal combustion engines.

Flashback Propensity of Syngas Flames at High Pressure: Diagnostic and Control

2010 ◽  
Author(s):  
S. Daniele ◽  
P. Jansohn ◽  
K. Boulouchos
Keyword(s):  
Control System ◽  
Gas Turbine ◽  
Turbulent Flame ◽  
Back Propagation ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Experimental Facility ◽  
Inlet Velocity ◽  
Turbulent Flame Speed

Nowadays, the establishment of IGCC (integrated gasification combined cycle) plants, prompts a growing interest in synthetic fuels for gas turbine based power generation. This interest has as direct consequence the need for understanding of flashback phenomena for premixed systems operated with H2-rich gases. This is due to the different properties of H2 (e.g. reactivity and diffusivity) with respect to CH4 which lead to higher flame speeds in the case of syngases (mixtures of H2-CO). This paper presents the results of experiments at gas turbine like conditions (pressure up to 15 bar, 0.2 < Φ < 0.7, 577K < T0 < 674K) aimed to determine flashback limits and their dependence on the combustion parameters (pressure, inlet temperature and inlet velocity). For the experimental facility used for this work the back propagation of the flame is believed to happen into the boundary layer of the fuel/air duct. Flashback propensity was found to have an appreciable dependence on pressure and inlet temperature while the effects of inlet velocity variations are weak. Explanations for the dependence on these three parameters, based on consideration on laminar and turbulent flame speed data (from modeling and experiments), are proposed. Within the frame of this work, in order to avoid major damages, the experimental facility was equipped with an automatic control system for flashback described in the paper. The control system is able to detect flame propagation into the fuel/air supply, arrest it and restore safe operating conditions by moving the flame out of the fuel/air section without blowing it out. This avoids destruction of components (burner/mixing) and time consuming shut downs of the test rig.

Dynamics and Stability Limits of Syngas Combustion in a Swirl-Stabilized Combustor

2008 ◽  
Author(s):  
Raymond L. Speth ◽  
H. Murat Altay ◽  
Duane E. Hudgins ◽  
Ahmed F. Ghoniem
Keyword(s):  
High Speed ◽  
Equivalence Ratio ◽  
Fluid Dynamic ◽  
Flame Structure ◽  
Low Frequency ◽  
Operating Conditions ◽  
Video Data ◽  
Combustion Dynamics ◽  
Lean Blowout ◽  
Operating Modes

The combustion dynamics, stability bands and flame structure of syngas flames under different operating conditions are investigated in an atmospheric pressure swirl-stabilized combustor. Pressure measurements and high-speed video data are used to distinguish several operating modes. Increasing the equivalence ratio makes the flame more compact, and in general increases the overall sound pressure level. Very close to the lean blowout limit, a long stable flame anchored to the inner recirculation zone is observed. At higher equivalence ratios, a low frequency, low amplitude pulsing mode associated with the fluid dynamic instabilities of axial swirling flows is present. Further increasing the equivalence ratio produces unstable flames oscillating at frequencies coupled with the acoustic eigenmodes. Additionally, a second unstable mode, coupled with a lower eigen-mode of the system, is observed for flames with CO concentration higher than 50%. As the amount of hydrogen in the fuel is increased, the lean flammability limit is extended and transitions between operating regimes move to lower equivalence ratios.

Performance Evaluation of a Catalytic Flat Plate Fuel Reformer for Hydrogen-Rich Reformate

2013 ◽  
Author(s):  
Susanta K. Das ◽  
K. Joel Berry
Keyword(s):  
Flat Plate ◽  
Reaction Rates ◽  
Operating Conditions ◽  
Design Parameters ◽  
Practical Implementation ◽  
Channel Height ◽  
Inlet Temperature ◽  
Optimized Design ◽  
Two Dimensional ◽  
Transfer Coefficients

A two-dimensional computational fluid dynamics (CFD) model is used for reforming methane with the help of catalytic combustion and reformation in a catalytic flat plate reformer. The two-dimensional approach makes the computational model more realistic by eliminating the uncertainties introduced by heat and mass transfer coefficients used in one-dimensional models. It also increased its capability to capture the effect of design parameters such as catalyst thickness, reaction rates, inlet temperature and velocity, and channel height has on producing high purity reformate gas. In order to carry out parametric studies related to various design parameters, in our present work, we simulate the entire flat plate reformer domain by considering full electro-kinetics that provide guidance for the practical implementation of such design. We chose different designs and operating conditions in such a way which makes possible to build a catalytic flat plate fuel reformer prototype. Based on the CFD results obtained in this study, we built a first generation catalytic flat plate fuel reformer prototype using the optimized design parameters. The performance of the fuel reformer prototype is tested with a 5-cell high temperature PEM fuel cell stack.

Direct numerical simulation of H2/O2/N2 flames with complex chemistry in two-dimensional turbulent flows

1994 ◽  
Vol 281 ◽  
pp. 1-32 ◽  
Author(s):  
M. Baum ◽  
T. J. Poinsot ◽  
D. C. Haworth ◽  
N. Darabiha
Keyword(s):  
Heat Release ◽  
Turbulent Flows ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Flame Temperature ◽  
Molecular Transport ◽  
Tangent Plane ◽  
Turbulent Flames ◽  
Two Dimensional ◽  
Tangential Strain

Premixed H2/O2/N2 flames propagating in two-dimensional turbulence have been studied using direct numerical simulations (DNS: simulations in which all fluid and thermochemical scales are fully resolved). Simulations include realistic chemical kinetics and molecular transport over a range of equivalence ratios Φ (Φ = 0.35, 0.5, 0.7, 1.0, 1.3). The validity of the flamelet assumption for premixed turbulent flames is checked by comparing DNS data and results obtained for steady strained premixed flames with the same chemistry (flamelet ‘library’). This comparison shows that flamelet libraries overestimate the influence of stretch on flame structure. Results are also compared with earlier zero-chemistry (flame sheet) and one-step chemistry simulations. Consistent with the simpler models, the turbulent flame with realistic chemistry aligns preferentially with extensive strain rates in the tangent plane and flame curvature probability density functions are close to symmetric with near-zero means. For very lean flames it is also found that the local flame structure correlates with curvature as predicted by DNS based on simple chemistry. However, for richer flames, by contrast to simple-chemistry results with non-unity Lewis numbers (ratio of thermal to species diffusivity), local flame structure does not correlate with curvature but rather with tangential strain rate. Turbulent straining results in substantial thinning of the flame relative to the steady unstrained laminar case. Heat-release and H2O2 contours remain thin and connected (‘flamelet-like’) while species including H-atom and OH are more diffuse. Peak OH concentration occurs well behind the peak heat-release zone when the flame temperature is high (of the order of 2800 K). For cooler and leaner flames (about 1600 K and for an equivalence ratio below 0.5) the OH radical is concentrated near the reaction zone and the maximum OH level provides an estimate of the local flamelet speed as assumed by Becker et al. (1990).

Fuel-Forced Flame Response of a Lean-Premixed Combustor

2011 ◽  
Author(s):  
Poravee Orawannukul ◽  
Jong Guen Lee ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Flow Rate ◽  
Equivalence Ratio ◽  
Operating Conditions ◽  
Chemiluminescence Intensity ◽  
Combustion Dynamics ◽  
Lean Premixed ◽  
Flame Response ◽  
Rate Of Heat Release ◽  
The Relationship

The response of a swirl-stabilized flame to equivalence ratio fluctuations is experimentally investigated in a single-nozzle lean premixed combustor. Equivalence ratio fluctuations are produced using a siren device to modulate the flow rate of fuel to the injector, while the air flow rate is kept constant. The magnitude and phase of the equivalence ratio fluctuations are measured near the exit of the nozzle using an infrared absorption technique. The flame response is characterized by the fluctuation in the flame’s overall rate of heat release, which is determined from the total CH* chemiluminescence emission from the flame. The relationship between total CH* chemiluminescence intensity and the flame’s overall rate of heat release is determined from a separate calibration experiment which accounts for the nonlinear relationship between chemiluminescence intensity and equivalence ratio. Measurements of the normalized equivalence ratio fluctuation and the normalized rate of heat release fluctuation are made over a range of modulation frequencies from 200 Hz to 440 Hz, which corresponds to Strouhal numbers from 0.4 to 2.8. These measurements are used to determine the fuel-forced flame transfer function which expresses the relationship between the equivalence ratio and rate of heat release fluctuations in terms of a gain and phase as a function of frequency. In addition, phase-synchronized CH* chemiluminescence images are captured to study the dynamics of the flame response over the modulation period. These measurements are made over a range of operating conditions and the results are analyzed to identify and better understand the mechanisms whereby equivalence ratio fluctuations result in fluctuations in the flame’s overall rate of heat release. Such information is essential to guide the formulation and validation of analytical fuel-forced flame response models and hence to predict combustion dynamics in gas turbine combustors.

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