Investigation of Stability Limits of a Premixed Counter Flame

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
H.A. Abdul Wahhab
Keyword(s):  
Equivalence Ratio ◽  
Analytical Study ◽  
Narrow Range ◽  
Flame Stability ◽  
Local Flow ◽  
Fuel Gas ◽  
Liquid Petroleum Gas ◽  
Air Flow Velocity ◽  
The Stability ◽  
Stability Limits

In combustion operations, flame fronts are often spread in an irregular. Therefore, the temperature and flame speed varies along the flame's front and depend on the asymmetry of the composition of the mixture and the conditions of the local flow before the flame, especially this behavior is evident in double counter flames. This paper describes an analytical study of stability limits of premixed counter flame. The investigation is based on experiments carried out to identify the effect of varying the distance between upper and lower burner edges on the stability limits at different equivalence ratio values; liquid petroleum gas (LPG) was used as fuel in experiments. The blow-off limit, disc flame limit, and double flame limit were investigated. Under the change of fuel gas-air flow velocity, in this type of flames, the conical flame is transformed into mushroom-shaped tented flame attached to the widened convex apex in the medial distance between the upper and lower burner edges. The experimental data and numerical analysis obtained show that high-stability for double flame, fuel-rich premixed flame operate over narrow range of equivalence ratio φ from 0.43 to 1.41. The ANSYS 17.0 FLUENT Premixed Flamelet Module with pre-processing was used. The results appear that increasing distance between burner edges decreases the flame stability efficiency. 

Experimental Investigation of CH4 and C3H8 Combustion in a Packed Bed Burner

2011 ◽  
Author(s):  
H. B. Gao ◽  
Z. G. Qu ◽  
W. Q. Tao ◽  
T. J. Lu
Keyword(s):  
Equivalence Ratio ◽  
Packed Bed ◽  
Pollutant Emissions ◽  
Flame Stability ◽  
Nox Emissions ◽  
Flame Thickness ◽  
Porous Burner ◽  
Hc Emissions ◽  
The Stability ◽  
Stability Limits

The main object of this work is to investigate combustion in a two-layer packed beds porous burner, in particular, to study the effect of methane and propane on flame stability, pressure drop and pollutant emissions. The equivalence ratio of both methane and propane varied from 0.55 to 0.70. The results indicated that flame stability limits of both methane and propane enlarged with the increasing of equivalence ratio, however, the stability limits of methane is more widely than propane. The macroscopic flame shapes of methane and propane remains approximately the same but the later has a larger flame thickness. The NOx emissions are seen to be increased and the CO decreased with the equivalence ratio, HC emissions firstly decreased and then increased with the equivalence ratio for both methane and propane.

Stability Limits of Premixed Methane-Air Microflames for Micropower Generation

2006 ◽  
Vol 326-328 ◽  
pp. 1133-1136
Author(s):  
Oh Chae Kwon ◽  
K.H. Lee ◽  
H.S. Ko ◽  
T. Kim
Keyword(s):  
Atmospheric Pressure ◽  
Equivalence Ratio ◽  
Heat Losses ◽  
Rich Region ◽  
Realistic Condition ◽  
Heat Recirculation ◽  
Micropower Generation ◽  
Tube Exit ◽  
The Stability ◽  
Stability Limits

Stability limits of premixed microflames were experimentally and computationally studied in order to understand the fundamental behavior of the flames when applied for micropower generation. Single microflames were generated on microtubes with inner diameters of 300-420 μm for methane-air mixtures at temperatures of 298-400 K and atmospheric pressure. For all the microflames at normal temperature, the stability limits were observed in a fuel-rich region, which is different from conventional macroflames exhibiting fuel-lean stability limits. Similar to the macroflames, however, the stability limits of the microflames show C-shaped curves in a tube exit Reynolds number (Re) – fuel equivalence ratio diagram, due to insufficient residence times and heat losses. For elevated temperature that is realistic condition for micropower generation using a heat-recirculation concept, the stability limits were extended toward the fuel-leaner conditions. Numerically predicted structure of microflames near the critical point (that is defined as the fuel-leanest condition among the C-shaped fuel-rich stability limits) showed significant fuel-dilution immediately near the tube exit due to a low Re effect, explaining why the stability limits of microflames are observed only in the fuel-rich region. Microcombustors for micropower generation should be designed to completely consume fuel for better performance.

scholarly journals Experimental Study of Biogas–Hydrogen Mixtures Combustion in Conventional Natural Gas Systems

2021 ◽  
Vol 11 (14) ◽  
pp. 6513
Author(s):  
Isabel Amez ◽  
Blanca Castells ◽  
Bernardo Llamas ◽  
David Bolonio ◽  
María Jesús García-Martínez ◽  
...  
Keyword(s):  
Natural Gas ◽  
Flame Stability ◽  
Exhaust Gas ◽  
Gas Temperature ◽  
Fuel Gas ◽  
Hydrogen Mixtures ◽  
The Stability ◽  
Exhaust Gas Temperature ◽  
Conventional Systems ◽  
Work Up

Biogas is a renewable gas with low heat energy, which makes it extremely difficult to use as fuel in conventional natural gas equipment. Nonetheless, the use of hydrogen as a biogas additive has proven to have a beneficial effect on flame stability and combustion behavior. This study evaluates the biogas–hydrogen combustion in a conventional natural gas burner able to work up to 100 kW. Tests were performed for three different compositions of biogas: BG70 (30% CO2), BG60 (40% CO2), and BG50 (50% CO2). To achieve better flame stability, each biogas was enriched with hydrogen from 5% to 25%. The difficulty of burning biogas in conventional systems was proven, as the burner does not ignite when the biogas composition contains more than 40% of CO2. The best improvements were obtained at 5% hydrogen composition since the exhaust gas temperature and, thus, the enthalpy, rises by 80% for BG70 and 65% for BG60. The stability map reveals that pure biogas combustion is unstable in BG70 and BG60; when the CO2 content is 50%, ignition is inhibited. The properties change slightly when the hydrogen concentrations are more than 20% in the fuel gas and do not necessarily improve.

scholarly journals Experimental study of the effects of swirl and air dilution on biogas non-premixed flame stability

2015 ◽  
Vol 19 (6) ◽  
pp. 2161-2169 ◽  
Author(s):  
Amir Rowhani ◽  
Sadegh Tabejamaat
Keyword(s):  
Carbon Dioxide ◽  
Flame Structure ◽  
Premixed Flame ◽  
Flame Stability ◽  
Negative Effects ◽  
Air Stream ◽  
The Stability ◽  
Carbon Dioxide Co2 ◽  
Flame Behavior ◽  
Stability Limits

An experimental investigation of the stability limits of biogas in a swirling non-premixed burner has been carried out. A mixture of 60% methane (CH4) and 40% carbon dioxide (CO2) was used to reach the typical biogas composition. Vane swirlers with 30?, 45? and 60? angles were used to make the swirling air. The biogas stability limits and flame behavior under swirling conditions were tested. Besides, effects of air dilution with nitrogen (N2) and CO2 on biogas stability limits were investigated. The results show that using swirl can enhance the flame stability limits approximately four or five times comparing to non-swirling air stream. Adding N2/CO2 to the air had negative effects on the flame stability but no changes were observed in the flame structure. The maximum air dilution was also obtained when 27% and 15% N2 was added to the swirling air under strong and weak swirl, respectively.

scholarly journals The Influence of Tailpipe Length on Flame Stability

1967 ◽  
Author(s):  
Louis G. Palermo ◽  
John R. O’Loughlin
Keyword(s):  
High Velocity ◽  
Test Section ◽  
Equivalence Ratio ◽  
Bluff Body ◽  
Flame Stability ◽  
A Value ◽  
Satisfactory Correlation ◽  
Air Stream ◽  
The Stability ◽  
Correlation Procedure

The influence of tailpipe length on the stability of a flame anchored in a high-velocity propane-air stream contained in a 2-in. pipe test section has been experimentally examined. Two flameholders were studied; a bluff body and a reverse-jet. A satisfactory correlation of the bluff-body data was obtained by plotting (blowoff velocity) (tailpipe length) 0.31 versus equivalence ratio. For the reverse-jet, the correlation procedure yielded a value of 0.64 for the exponent on tailpipe length but the correlation was poorer. A better correlation of the bluff-body data was obtained when the exponent on tailpipe length was taken as a function of equivalence ratio.

Numerical study of the flame stability of premixed methane–air combustion in a combined porous-free flame burner

2018 ◽  
Vol 233 (4) ◽  
pp. 530-544 ◽  
Author(s):  
Seyed Mohammad Hashemi ◽  
Seyed Abdolmehdi Hashemi
Keyword(s):  
Equivalence Ratio ◽  
Numerical Study ◽  
Flame Stabilization ◽  
Pollutant Emissions ◽  
Pollutant Emission ◽  
Flame Stability ◽  
Emission Analysis ◽  
Porous Burner ◽  
Flame Burner ◽  
Stability Limits

Premixed methane–air combustion process within a combined porous-free flame burner was investigated numerically in the present study. The burner consisted of a perforated porous ceramic pellet forming combination of submerged and free flame zones. Nonequilibrium thermal condition between the gas and solid phases was implemented and governing equations were solved in a two-dimensional model using finite volume method. Detailed chemistry based on reduced GRI 3.0 mechanism with 41 reaction steps and 16 species including NOx mechanisms was utilized to simulate the combustion processes and pollutant emissions. In order to investigate the validation of the implemented numerical model, the burner was manufactured and tested. The predicted results were consistent with the experimental data. Comparison of the combined porous-free flame burner with porous burner showed that the flame stability limits of the combined burner were higher than those of porous burner. Multimode heat transfer within the porous medium was perused and the effect of heat recirculation on the flame stabilization was discussed. Investigation of the effect of pore density on the flame stabilization showed that the lower pore densities were desirable in order to improve the flame stability limits. Pollutant emission analysis proved that the NO concentration increased with increasing the equivalence ratio while the minimum quantity of CO concentration was evaluated at an equivalence ratio of 0.6.

Analysis of LPG diffusion flame in tube type burner

2019 ◽  
Vol 13 (3) ◽  
pp. 5278-5293
Author(s):  
Vipul Patel ◽  
Rupesh Shah
Keyword(s):  
Diffusion Flame ◽  
Emission Characteristic ◽  
Flame Stability ◽  
Liquefied Petroleum Gas ◽  
Air Velocity ◽  
Length Fraction ◽  
Low Emission ◽  
Tube Type ◽  
Stability Limits ◽  
Co Emission

The present research aims to analyse diffusion flame in a tube type burner with Liquefied petroleum gas (LPG) as a fuel. An experimental investigation is performed to study flame appearance, flame stability, Soot free length fraction (SFLF) and CO emission of LPG diffusion flame. Effects of varying air and fuel velocities are analysed to understand the physical process involved in combustion. SFLF is measured to estimate the reduction of soot. Stability limits of the diffusion flame are characterized by the blowoff velocity. Emission characteristic in terms of CO level is measured at different equivalence ratios. Experimental results show that the air and fuel velocity strongly influences the appearance of LPG diffusion flame. At a constant fuel velocity, blue zone increases and the luminous zone decreases with the increase in air velocity. It is observed that the SFLF increases with increasing air velocity at a constant fuel velocity. It is observed that the blowoff velocity of the diffusion flame increases as fuel velocity increases. Comparison of emission for flame with and without swirl indicates that swirl results in low emission of CO and higher flame stability. Swirler with 45° vanes achieved the lowest CO emission of 30 ppm at Φ = 1.3.

Stability as a constraint in sagittal plane human force exertion modeling

1998 ◽  
Vol 1 (1) ◽  
pp. 23-39
Author(s):  
Carter J. Kerk ◽  
Don B. Chaffin ◽  
W. Monroe Keyserling
Keyword(s):  
Muscle Strength ◽  
Ankle Joint ◽  
Coefficient Of Friction ◽  
Sagittal Plane ◽  
Biomechanical Model ◽  
Whole Body ◽  
The Stability ◽  
Joint Center ◽  
Static Conditions ◽  
Stability Limits

The stability constraints of a two-dimensional static human force exertion capability model (2DHFEC) were evaluated with subjects of varying anthropometry and strength capabilities performing manual exertions. The biomechanical model comprehensively estimated human force exertion capability under sagittally symmetric static conditions using constraints from three classes: stability, joint muscle strength, and coefficient of friction. Experimental results showed the concept of stability must be considered with joint muscle strength capability and coefficient of friction in predicting hand force exertion capability. Information was gained concerning foot modeling parameters as they affect whole-body stability. Findings indicated that stability limits should be placed approximately 37 % the ankle joint center to the posterior-most point of the foot and 130 % the distance from the ankle joint center to the maximal medial protuberance (the ball of the foot). 2DHFEC provided improvements over existing models, especially where horizontal push/pull forces create balance concerns.

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.

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