The Effect of the Corner Recirculation Zone on Separated Stratified Swirling Flames and Combustion Instabilities

2019 ◽  
Author(s):  
Heng Song ◽  
Xiao Han ◽  
Yuzhen Lin ◽  
Chi Zhang ◽  
Xin Hui ◽  
...  
Keyword(s):  
Equivalence Ratio ◽  
Passive Control ◽  
Recirculation Zone ◽  
Acoustic Oscillation ◽  
Potential Method ◽  
Suppressive Effect ◽  
Operating Conditions ◽  
Sudden Increase ◽  
Combustion Instabilities ◽  
Swirling Flames

Abstract The present work investigates effects of the corner recirculation zone (CRZ) on flame macrostructures and combustion instabilities in the Beihang Axial Swirler Independently Stratified (BASIS) burner, a double-swirled full-scale burner characterized by separated stratified swirling flames at atmospheric pressure supplied with methane/air mixture. Three different macrostructures are observed, i.e. a lifted L-flame, a double-conical S-flame and a single conical V-flame as the stratification ratio (SR, the ratio of the inner stream equivalence ratio to the outer stream equivalence ratio) varies from 0.25 to 2.50 at a fixed total equivalence ratio of 0.6. It is found that the penetration of the flame into the corner recirculation zone leads to a sudden increase of acoustic oscillation. Rayleigh index maps confirm the driving effect of the CRZ region on combustion instabilities for the 0.25 ≤ SR ≤ 1.75 cases. When the corner recirculation zone is removed by the use of segmented confinements, similar flame macrostructures arise in the same SR range. More interestingly, the combustion instability is suppressed under all stratification ratios. A parametric experiment is also performed to confirm the generality of above findings, including three types of the segmented confinement, two premixednesses of the outer flame and a wider range of operating conditions. The suppressive effect is outstanding in all segmented confinements. The present study reveals the effect of the corner recirculation zone on combustion instabilities and demonstrates a potential method for passive control.

A Novel Strategy for Passive Control of Combustion Instabilities Through Modification of Flame Dynamics

2008 ◽  
Author(s):  
Nicolas Noiray ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Se´bastien Candel
Keyword(s):  
Passive Control ◽  
Full Range ◽  
Premixed Flames ◽  
Perforated Plate ◽  
Operating Conditions ◽  
System Stability ◽  
Injection System ◽  
Coherent Motion ◽  
Dynamical Response ◽  
Combustion Instabilities

Passive control of combustion instabilities is explored in the case of systems featuring a collection of premixed flames. The method devised in this research differs from the general strategies employed to passively hinder the growth of acoustic-combustion oscillations by augmenting acoustic damping. Dissipation of acoustic energy is usually obtained by connecting Helmholtz resonators or quarter wave type cavities or by placing perforated plate linings around the system. While these systems effectively reduce pressure oscillations, optimum performance is not always obtained over the full range of operating conditions and their implementation requires substantial space which is not often available in practice. Conceptually, these standard techniques deal with the consequences of combustion instabilities but not with the driving sources. It is shown here that an alternative solution may be to directly act on the causes of the onset of thermo-acoustic coupling. The basic idea is to modify the flames dynamics using the dynamical response of the injection system. The principle of the passive control strategy proposed on this basis is to counteract the onset of oscillations by tackling the underlying causes. The injection system is modified to avoid a coherent motion of the flames when they are submitted to an acoustic modulation and reduce the coupling between acoustic perturbations and heat release fluctuations. Numerical simulations and experimental data are presented and one may infer that the method could bring a substantial improvement to the system stability. The efficiency of this technique is demonstrated in the case of small premixed flames anchored on a multipoint injection system (the configuration is that of a premixed gaseous-fueled multipoint dump combustor), but the principle is more general and can be extended to larger scale turbulent combustors featuring a collection of flames.

scholarly journals Injector-coupled transverse instabilities in a multi-element premixed combustor

2020 ◽  
Vol 12 ◽  
pp. 175682772093283
Author(s):  
John J Philo ◽  
Rohan M Gejji ◽  
Carson D Slabaugh
Keyword(s):  
Equivalence Ratio ◽  
Pressure Fluctuations ◽  
High Amplitude ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Combustion Dynamics ◽  
Thermoacoustic Instabilities ◽  
Transverse Modes ◽  
Additional Mode ◽  
The Relationship

Combustion instabilities in a high-pressure, multi-element combustor are studied in order to understand the relationship between the chamber and injector dynamics. A linear array of seven injectors supplies premixed natural gas and air into a rectangular combustion chamber designed to promote high-frequency, transverse thermoacoustic instabilities. The effect of equivalence ratio on the combustion dynamics was investigated for two injector lengths, 62.5 and 125 mm. For all operating conditions, the 125 mm injectors promote high-amplitude instabilities of the fundamental transverse (1T) mode, which has a frequency of 1750–1850 Hz. Reducing the injector length significantly lowers the instability amplitudes for all operating conditions and, for lower equivalence ratio cases, excites an additional mode near 1550 Hz. The delineating feature controlling the growth of the instabilities in each injector configuration is the coupling with axial pressure fluctuations in the injectors that occur in response to the transverse modes in the chamber.

Ion Kinetic Energy Determinations in Radio-Frequency Glow Discharge Mass Spectrometry

1995 ◽  
Vol 49 (7) ◽  
pp. 917-926 ◽  
Author(s):  
Paula R. Cable ◽  
R. Kenneth Marcus
Keyword(s):  
Kinetic Energy ◽  
Glow Discharge ◽  
Radio Frequency ◽  
Source Region ◽  
Potential Method ◽  
Operating Conditions ◽  
Atmospheric Plasma ◽  
Radio Frequency Glow Discharge ◽  
Ion Trajectory ◽  
Ion Kinetic Energy

Radio-frequency glow discharge (rf-GD) sources produce an abundance of both atoms and ions. For the mass spectrometric application of the glow discharge technique, knowledge of the ion kinetic energies is required to optimize extraction and focusing of ions from the source region into the analyzer. This paper details kinetic energies experimentally determined with the use of the “retarding potential” method. For this study, the analyzer quadrupole of a double-quadrupole mass spectrometer was positively biased to act as a repeller. Ion kinetic energies (IKEs) determined for a variety of discharge and analyzer operating conditions ranged from 12.5 eV to 25.0 eV for 63Cu+. Kinetic energy measurements were confirmed from ion trajectory simulations and follow closely the experimental values for identical analyzer conditions and initial IKEs. Results of this study indicate that the conditions under which ions are formed (plasma conditions) affect IKEs and energy spreads to a greater extent than analyzer parameter variations. Different from atmospheric plasma sources, IKEs for rf-GD species do not vary as a function of ion mass/identity. Evidence is also given in support of a slight mass biasing owing to the transmission properties of double-quadrupole analyzers. The findings detailed herein demonstrate the effects of rf modulation on both ion kinetic energy values and distributions.

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.

scholarly journals Combined Effects of EMBr and SEMS on Melt Flow and Solidification in a Thin Slab Continuous Caster

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 948
Author(s):  
Changjun Wang ◽  
Zhongqiu Liu ◽  
Baokuan Li
Keyword(s):  
Continuous Caster ◽  
Solidification Rate ◽  
Potential Method ◽  
Suppressive Effect ◽  
Thin Slab ◽  
Dispersion Effect ◽  
Melt Flow ◽  
Simultaneous Application ◽  
Iron And Steel ◽  
Slab Continuous Caster

Electromagnetic fields have emerged as powerful tools for addressing current problems in thin slab continuous casting processes in the iron and steel industry. Substantial studies have been undertaken on the fundamental effects of electromagnetic brakes (EMBr) and strand electromagnetic stirring (SEMS). However, little attention has been focused on melt flow and solidification in a thin slab continuous caster with the simultaneous application of an EMBr and SEMS. The present study aimed to predict transient fields in the caster using a large eddy simulation and an enthalpy-porosity method. The electric potential method was applied in the braking process, and the conductivity change with solidification was considered. The suppressive effect on the intensity of the nozzle jet, the balance effect on the mold flow, and a dispersion effect could be observed. The dispersion effect was a novel finding and was beneficial to a flatter nozzle jet. In contrast, SEMS caused a highly turbulent flow in the strand. A large vortex could be observed in the casting direction. The solidified shell became more uniform, and the solidification rate became obviously slower. These findings supported the view that a high-quality thin slab can be produced by the application of an EMBr and SEMS.

Extraction and Identification of Vitamin E from Pithecellobium Jiringan Seeds Using Supercritical Carbon Dioxide

2015 ◽  
Vol 74 (7) ◽  
Author(s):  
Mohd Azizi Che Yunus ◽  
Salman Zhari ◽  
Saharudin Haron ◽  
Nur Husnina Arsad ◽  
Zuhaili Idham ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Vitamin E ◽  
Supercritical Carbon Dioxide ◽  
Potential Method ◽  
Operating Conditions ◽  
Oil Yield ◽  
Flight Mass Spectrometry ◽  
Carbon Dioxide Extraction ◽  
Natural Herb ◽  
Supercritical Carbon

Pithecellobium Jiringan (P. Jiringan) is traditionally known as natural herb consists of several medicinal compounds (vitamin E). Supercritical carbon dioxide extraction (SC-CO2) has been proven as potential method to extract interest compound from herbs. By altering pressure and temperature, the specific compound can be extracted. In this study, the SC-CO2 operating conditions are pressure (20.68 MPa to 55.16 MPa) and temperature (40°C to 80°C) in one hour extraction regime was used to extract vitamin E from P. jiringan. The quantification of vitamin E was analysed with Gas Chromatography Time of Flight Mass Spectrometry (GC-TOF-MS). The responses are overall oil yield and vitamin E yield. The overall oil yield was obtained at the highest condition of 55.16 MPa and 80°C with asymptotic yield of 8.06%. In contrast, the highest amount of vitamin E obtained is 0.0458mg/g sample (80.14 ppm) at the lowest extraction condition of 20.68 MPa and 40ᵒC.

scholarly journals Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations

1998 ◽  
Author(s):  
Rajiv Mongia ◽  
Robert Dibble ◽  
Jeff Lovett
Keyword(s):  
Power Spectrum ◽  
Mole Fraction ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Pollutant Emissions ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Lean Premixed Combustion ◽  
Lean Premixed

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer. The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

2005 ◽  
Author(s):  
P. Griebel ◽  
R. Bombach ◽  
A. Inauen ◽  
R. Scha¨ren ◽  
S. Schenker ◽  
...  
Keyword(s):  
Flame Front ◽  
Gas Turbines ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Turbulent Flame Speed ◽  
Front Position ◽  
Preheating Temperature ◽  
Lean Premixed

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

Modelling of Thermoacoustic Combustion Instabilities Phenomena: Application to an Experimental Rig for Testing Full Scale Burners

2014 ◽  
Author(s):  
Davide Laera ◽  
Giovanni Campa ◽  
Sergio M. Camporeale ◽  
Edoardo Bertolotto ◽  
Sergio Rizzo ◽  
...  
Keyword(s):  
Acoustic Analysis ◽  
Fem Analysis ◽  
Full Scale ◽  
Operating Conditions ◽  
System Modelling ◽  
Combustion Instabilities ◽  
Test Rig ◽  
Pressure Oscillations ◽  
Secondary Air ◽  
Actual Geometry

This paper concerns the acoustic analysis of self–sustained thermoacoustic pressure oscillations that occur in a test rig equipped with full scale lean premixed burner. The experimental work is conducted by Ansaldo Energia and CCA (Centro Combustione Ambiente) at the Ansaldo Caldaie facility in Gioia del Colle (Italy), in cooperation with Politecnico di Bari. The test rig is characterized by a longitudinal development with two acoustic volumes, plenum and combustion chamber, coupled by the burner. The length of both chambers can be varied with continuity in order to obtain instability at different frequencies. A previously developed three dimensional finite element code has been applied to carry out the linear stability analysis of the system, modelling the thermoacoustic combustion instabilities through the Helmholtz equation under the hypothesis of low Mach approximation. The heat release fluctuations are modelled according to the κ-τ approach. The burner, characterized by two conduits for primary and secondary air, is simulated by means of both a FEM analysis and a Burner Transfer Matrix (BTM) method in order to examine the influence of details of its actual geometry. Different operating conditions, in which self–sustained pressure oscillations have been observed, are examined. Frequencies and growth rates of unstable modes are identified, with good agreement with experimental data in terms of frequencies and acoustics pressure wave profiles.

Experimental Investigation Into the High Altitude Relight of a Three-Cup Combustor Sector

2018 ◽  
Author(s):  
Michael J. Denton ◽  
Samir B. Tambe ◽  
San-Mou Jeng
Keyword(s):  
Pressure Drop ◽  
High Altitude ◽  
High Speed ◽  
Development Process ◽  
Recirculation Zone ◽  
Operating Conditions ◽  
Pressure Drops ◽  
High Speed Video ◽  
Air Jet ◽  
Flame Development

The altitude relight of a gas turbine combustor is an FAA and EASA regulation which dictates the successful re-ignition of an engine and its proper spool-up after an in-flight shutdown. Combustor pressure loss, ambient pressure, ambient temperature, and equivalence ratio were all studied on a full-scale, 3-cup, single-annular aviation combustor sector to create an ignition map. The flame development process was studied through the implementation of high-speed video. Testing was conducted by placing the sector horizontally upstream of an air jet ejector in a high altitude relight testing facility. Air was maintained at room temperature for varying pressure, and then the cryogenic heat exchanger was fed with liquid nitrogen to chill the air down to a limit of −50 deg F, corresponding with an altitude of 30,000 feet. Fuel was injected at constant equivalence ratios across multiple operating conditions, giving insight into the ignition map of the combustor sector. Results of testing indicated difficulty in achieving ignition at high altitudes for pressure drops greater than 2%, while low pressure drops show adequate performance. Introducing low temperatures to simulate the ambient conditions yielded a worse outcome, with all conditions having poor results except for 1%. High-speed video of the flame development process during the relight conditions across all altitudes yielded a substantial effect of the pressure drop on ignitability of the combustor. An increase in pressure drop was associated with a decrease in the likelihood of ignition success, especially at increasing altitudes. The introduction of the reduced temperature effect exacerbated this effect, further hurting ignition. High velocity regions in the combustor were detrimental to the ignition, and high area, low velocity regions aided greatly. The flame tended to settle into the corner recirculation zone and recirculate back into the center-toroidal recirculation zone (CTRZ), spreading downstream and likewise into adjacent swirl cups. These tests demonstrate the need for new combustor designs to consider adding large recirculation zones for combustor flame stability that will aid in relight requirements.

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