Stability and Liftoff of a N2-in-H2 Jet Flame in a Vitiated Co-flow at Atmospheric Pressure

2014 ◽  
Vol 16 (2-3) ◽  
pp. 129 ◽  
Author(s):  
A. North ◽  
D. Frederick ◽  
J.-Y. Chen ◽  
R. Dibble ◽  
A. Gruber
Keyword(s):  
Flame Propagation ◽  
Equivalence Ratio ◽  
Jet Flame ◽  
Environment Temperature ◽  
Flow Equivalence ◽  
Nitrogen Dilution ◽  
Height Dependence ◽  
Jet Velocity ◽  
The Stability ◽  
Stability Regime

<p>The stability and liftoff characteristics of a nitrogen (N<sub>2</sub>) diluted hydrogen (H<sub>2</sub>) jet flame in a vitiated co-flow are investigated experimentally with particular attention focused on regimes where multiple stabilization mechanisms are active. Information gleaned from this research is instrumental for informing modeling approaches in flame transition situations when both autoignition and flame propagation influence combustion characteristics. Stability regime diagrams which outline the conditions under which the flame is attached, lifted, blown-out, and unsteady are experimentally developed and explored. The lifted regime is further characterized in determining liftoff height dependence on N<sub>2</sub> dilution, jet velocity, and co-flow equivalence ratio (or essentially, co-flow temperature). A strong sensitivity of liftoff height to N<sub>2</sub> dilution, jet velocity, and co-flow equivalence ratio is observed. Liftoff heights predicted by Kalghatgi’s correlation are unable to capture the effects of N<sub>2</sub> dilution on liftoff height for the heated co-flow cases. A uniquely formulated Damköhler number, where the chemical time scale is based on flame propagation rather than autoignition, was therefore developed which acceptably captures the effects of jet velocity, nitrogen dilution and environment temperature on liftoff height. Satisfactory agreement between the correlation results indicate that stabilization is dominated by propagation, and prior studies with similar flames, such as the research of Muñiz and Mungal (1997) indicate that the propagating flame is likely tribrachial.</p>

scholarly journals Effect of Pressure, Environment Temperature, Jet Velocity and Nitrogen Dilution on the Liftoff Characteristics of a N2-in-H2 Jet Flame in a Vitiated Co-flow

2014 ◽  
Vol 16 (2-3) ◽  
pp. 141 ◽  
Author(s):  
A. North ◽  
M. Magar ◽  
J.-Y. Chen ◽  
R. Dibble ◽  
A. Gruber
Keyword(s):  
Gas Turbines ◽  
Operating Conditions ◽  
Flame Stability ◽  
High Hydrogen ◽  
Jet Flame ◽  
Environment Temperature ◽  
Nitrogen Dilution ◽  
Air Mixing ◽  
Partially Premixed ◽  
Jet Velocity

<p>The CO<sub>2</sub> emission prevention advantage of generating power with high hydrogen content fuels using gas turbines motivates an improved understanding of the ignition behavior of hydrogen in premixed and partially premixed environments. Hydrogen rich fueled flame stability is sensitive to operating conditions, including environment pressure, temperature, and jet velocity. Furthermore, when premixed or partially premixed operation is needed for nitric oxide emissions reduction, a diluent, such as nitrogen, is often added in allowing fuel/air mixing prior to combustion. Thus, the concentration of the diluent added is an additional independent variable on which flame stability dependence is needed. The focus of this research is on characterizing the dependence of hydrogen jet flame stability on environment temperature, pressure, jet velocity and diluent concentration by determining the dependence of the liftoff height of lifted flames on these 4 independent parameters. Nitrogen is used as the diluent due to its availability and effectiveness in promoting liftoff. A correlation modeling the liftoff height dependence on operating conditions is developed which emphasizes the factors that bear the greatest impact on ignition behavior.</p>

Effect of Equivalence Ratio and Burner Geometry on the Characteristics of Laminar Premixed Flames at Moderate Coflow

2004 ◽  
Author(s):  
P. Hariharan ◽  
S. R. Gollahalli
Keyword(s):  
Aspect Ratio ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Combustion Efficiency ◽  
Flame Height ◽  
No Production ◽  
Air Velocity ◽  
Burner Flame ◽  
Jet Velocity ◽  
The Stability

The importance of studying laminar premixed flames lies in applications such as gas ranges and ovens, heating appliances and Bunsen burners. With the current demand for large amounts of economical, clean power, there is a need for research in increasing the combustion efficiency. Laminar premixed Propane/Hydrogen/Air flames with 3 m/s coflow and without coflow, with a variation of jet equivalence ratio (JEQ) from 0.5 to 4 for 20 m/s jet velocity, have been studied experimentally to determine the interactions of burner geometry of premixed flames and coflow. Two different burner geometries (circular burner, and 3:1 aspect ratio (AR) burners) were used in the experiments. The stability tests indicated that for 20 m/s jet velocity both at quiescent and coflow conditions the circular burner was more stable than the 3:1AR elliptical burner. Flame height studies indicated that circular burner flames were taller than the 3:1AR elliptical burner flames. However, there was a reduction in flame height when coflow air velocity of 3 m/s was introduced. Temperature profile indicated a higher peak temperature for circular burners followed by elliptical burner, both at quiescent and coflow conditions. The introduction of moderate coflow showed a decrease in NO production rate. In order to explain the structure of the flame in detail and various mechanisms that lead to the explanation of global flame characteristics, inflame concentration measurements were taken in near burner (25% of flame height), mid burner (50% of flame height) and far burner (75% of flame height) regions of the flame.

scholarly journals Studies on Lean-Blowout Characteristics of a Premixed Jet Flame

1995 ◽  
Author(s):  
Viswanath R. Katta ◽  
W. M. Roquemore
Keyword(s):  
Equivalence Ratio ◽  
Ambient Air ◽  
Computational Domain ◽  
Detailed Chemical Kinetics ◽  
Jet Flame ◽  
Fuel Jet ◽  
Wide Range ◽  
The Stability ◽  
Dependent Transport ◽  
Fuel Tube

The stability characteristics of a fuel-lean premixed jet flame are investigated using a time-dependent, axisymmetric numerical model with a detailed-chemical-kinetics mechanism for H2-O2-N2 combustion. Temperature- and species-dependent transport properties are incorporated. The mathematical model is validated by computing the burning velocities for different equivalence ratios and comparing them with experimentally measured values. Premixed flames that are stably attached to the fuel tube are obtained over a wide range of equivalence ratios. The lower limit for equivalence ratio at which the flame lifts-off from the fuel tube is found to be 0.4. Calculations have also correctly predicted the following scenario: when a premixed flame lifts-off at the base, it becomes unstable and is eventually blown out of the computational domain. The blow-out process is studied by analyzing the stable flame at Φ = 0.4 and the unstable flame at Φ = 0.395. Entrainment of ambient air by the fuel jet upstream of the lifted-flame base reduces the local equivalence ratio which, in turn, is found to be responsible for the blow-out of the flame.

scholarly journals Effect of Temperature Conditions on Flame Evolutions of Turbulent Jet Ignition

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2226
Author(s):  
Jiaying Pan ◽  
Yu He ◽  
Tao Li ◽  
Haiqiao Wei ◽  
Lei Wang ◽  
...  
Keyword(s):  
Flame Propagation ◽  
Early Stage ◽  
Turbulent Jet ◽  
Combustion Stability ◽  
Effect Of Temperature ◽  
Main Chamber ◽  
Detailed Chemical Kinetics ◽  
Jet Flame ◽  
Spherical Flame ◽  
Temperature Conditions

Turbulent jet ignition technology can significantly improve lean combustion stability and suppress engine knocking. However, the narrow jet channel between the pre-chamber and the main chamber leads to some difficulties in heat exchange, which significantly affects combustion performance and mechanical component lifetime. To clarify the effect of temperature conditions on combustion evolutions of turbulent jet ignition, direct numerical simulations with detailed chemical kinetics were employed under engine-relevant conditions. The flame propagation in the pre-chamber and the early-stage turbulent jet ignition in the main chamber were investigated. The results show that depending on temperature conditions, two types of flame configuration can be identified in the main chamber, i.e., the normal turbulent jet flame propagation and the spherical flame propagation, and the latter is closely associated with pressure wave disturbance. Under low-temperature conditions, the cold jet stoichiometric mixtures and the vortexes induced by the jet flow determine the early-stage flame development in the main chamber. Under intermediate temperature conditions, pre-flame heat release and leading pressure waves are induced in the jet channel, which can be regarded as a transition of different combustion modes. Whereas under high-temperature conditions, irregular auto-ignition events start to occur, and spherical flame fronts are induced in the main chamber, behaving faster flame propagation.

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

2021 ◽  
Author(s):  
Jihang Li ◽  
Hyunguk Kwon ◽  
Drue Seksinsky ◽  
Daniel Doleiden ◽  
Jacqueline O’Connor ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Breakdown Region ◽  
Large Eddy ◽  
Rate Oscillations ◽  
Combustion Oscillation ◽  
The Stability ◽  
The Impact

Abstract Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot gases as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot flame efficacy increases with pilot flame equivalence ratio until it matches the main flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. The simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

Technology and Effectiveness of Cast Iron Treatment by Gas Injection

2010 ◽  
Vol 457 ◽  
pp. 459-464
Author(s):  
Edis B. Ten
Keyword(s):  
Cast Iron ◽  
Gas Injection ◽  
Small Diameter ◽  
Multiple Use ◽  
Positive Effects ◽  
Injection Treatment ◽  
The Stability ◽  
Injection Technology ◽  
Stability Regime ◽  
Structure Stabilization

In this work the development of the technology and equipment for gas injection treatment of cast iron by inert gas (nitrogen) is presented. The equipment includes the plunging lance as a lined steel pipe with nozzles. The nozzles are thin channels, which are lined by ceramic tubes with small-diameter. The lance has a multiple use, as it has calibrated channel sizes, and provide the stability regime of gas injection treatment. The characteristic of the gas injection technology consists of blowing of melt by gas, which is injected into the liquid cast iron through thin jet with a speed near to the velocity of sound. In this case, the dispersion of gas jets in small-sized bubbles is reached, therefore the refining effectiveness increases. The gas injection treatment shows the promotion of casting properties, improvement of homogeneity and fineness of structure, stabilization or increasing of mechanical properties, decreasing of casting defectiveness. The positive effects of the gas injection treatment is the result of complex action of the injecting gas into the cast iron melt. Together with refining and homogenizing action at specified conditions, it offers the modifying and alloying effects also.

Dielectric Elastomer as a New Material for Electrostatically Actuated Microbeams: Stability Analysis

2019 ◽  
Vol 11 (10) ◽  
pp. 1950098
Author(s):  
Mohammad Fathalilou ◽  
Pegah Rezaei-Abajelou ◽  
Afsoon Vefaghi ◽  
Ghader Rezazadeh
Keyword(s):  
Pitchfork Bifurcation ◽  
Dielectric Elastomer ◽  
Micro Electro Mechanical Systems ◽  
High Deformation ◽  
Electrostatically Actuated ◽  
Eigen Value ◽  
Deformation Ability ◽  
New Material ◽  
The Stability ◽  
Stability Regime

Due to the interesting properties such as light weight and high deformation ability, dielectric elastomer (DE) resonators can be good alternatives for conventional silicon resonant beams used in micro-electro-mechanical systems (MEMS). This paper proposes a modeling in which a pre-stretched clamped-clamped DE-based microbeam oscillating above the ground substrate is subjected to an external electrostatic pressure. Using a DE-based beam affects the total rigidity of the system, which may lead to an anticipated saddle-node or pitchfork bifurcation. Hence, the present study tries to analyze the effects of DE properties on changing the stability regime of DE-based microbeams under electrostatic actuation. The stability of the system has been investigated using an eigen-value form of the problem. The effects of DE properties including pre-stress, relative permittivity and voltage value across the electrodes on pull-in or divergence instability as well as the frequency response of the system have been investigated. Moreover, the critical values of the DE voltage as a booster of instability occurrence have been obtained in either the presence or absence of the direct current (DC) voltage. It has been found that the pre-stress and appropriate DE permittivity can provide a needed magnitude of the DE actuating voltage to alter the resonance frequency and stability positions of the structure.

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