Flame Stability of a Micro Can-Type Afterburner for a SOFC

2008 ◽  
Author(s):  
Yuji Yahagi
Keyword(s):  
Flame Stabilization ◽  
Premixed Flame ◽  
Baffle Plate ◽  
Air Jets ◽  
Air Jet ◽  
Nonpremixed Flame ◽  
Air Mixing ◽  
Fuel Nozzle ◽  
Lean Fuel ◽  
Partially Premixed Flame

This paper is fundamental studies on an afterburner for a 20kW class home cogeneration solid oxide fuel cell (SOFC) hybrid system. The proposed burner is a micro size can-type with a baffle plate having multi air holes set annularly and an opposite arranged single fuel and air nozzle in the center. This geometry is suitable to enhance the fuel and air mixing and to stabilize the flame in the ultra lean fuel of the effluent from SOFC stack in the MGT. The blow off limits and flame shape are discussed with the flow structure behind the baffle plate which measured by using a particle image velocimetry (PIV). The formed flames can be classified into four groups which are a premixed flame, a partially premixed flame, a partially nonpremixed flame, and a nonpremixed flame depend on the pilot air jet velocity, the baffle plate holes air jets velocity, and the clearance of the fuel nozzle exit and baffle plate, even when the flow rate of the fuel is same. When the premixed flame formed side by the fuel nozzle, the fuel is preheated approximately 750K. The counter-rotating vortices are formed behind the baffle plate and the vortices play a key role for the fuel and air mixing as well as the flame stabilization. The pilot jet not only controlled the flame position but also enhanced the fuel and air mixing. Especially, the pilot jet is important to form the premixed flame near the blow off conditions, and the desirable velocity is close to the air jets velocity of the baffle plate holes. However, there are some ineffective conditions for the pilot air jet.

Large Eddy Simulation of Lifted Non-Premixed Jet Flames Using 2-Scalar Flamelet Model

2003 ◽  
Author(s):  
Mikikane Hirohata ◽  
Nobuyuki Taniguchi ◽  
Toshio Kobayashi
Keyword(s):  
Burning Velocity ◽  
Velocity Model ◽  
Flame Stabilization ◽  
Premixed Combustion ◽  
Premixed Flame ◽  
Jet Flames ◽  
Flamelet Model ◽  
The Difference ◽  
Partially Premixed Flame ◽  
Lift Off

In this paper we introduce the LES of lifted non-premixed jet flames based on two-scalar flamelet modeling. The flamelet G-equation for premixed combustion and the conserved scalar equation for non-premixed combustion are combined to express partially premixed flame propagation. In order to close filtered G-equation, the subgrid burning velocity model is proposed based on the concept that small triple flamelet are projected into unburnt gas from the flame-base of the lifted non-premixed flame. The calculation results are shown that wrinkling lifted flames are simulated and the difference of the lift-off height and the flame-shape with the variation of the co-flowing velocity is predicted. It is also confirmed that the conditional axial velocity near the flame base which is thought to relate the condition of the flame stabilization is on the order of two–three times of the laminar burning velocity, which agrees well with the experimental data. We hope that this method will be useful to investigate the flame stabilizing mechanism or flame controls of practical non-premixed jet flames.

Twin Pulsating Jets Impingement Heat Transfer for Fuel Preheating in Automotives

2014 ◽  
Vol 663 ◽  
pp. 322-328 ◽  
Author(s):  
Ali Ahmed Gitan ◽  
Rozli Zulkifli ◽  
Kamaruzaman Sopian ◽  
Shahrir Abdullah
Keyword(s):  
Heat Transfer ◽  
Ignition Process ◽  
Pulsation Frequency ◽  
Ir Camera ◽  
Copper Target ◽  
Air Jets ◽  
Air Jet ◽  
Impingement Heat Transfer ◽  
Pulsating Jet ◽  
Pulsating Jets

The problem of environmental pollution and depletion of fossil fuel can be reduced in automotives by using an alternative bio-fuel and improve the ignition process in engine. Both solutions need to use the fuel preheating technique. This work presents the idea of fuel preheating by using exhaust impingement on the fuel tank. Heat transfer between twin pulsating hot air jets and flat copper target was investigated as an application for preheating of automotive fuel to improve ignition process in the engine. The nozzle of 20 mm was used to produce air jet of Reynolds number, Re ≃ 5500 and a temperature of 54°C. The impinged target was imposed to still air surrounding at temperature of 24°C. Pulsating frequencies of 10-50 Hz were applied on air jets by using twin pulsating jet mechanism. The effect of pulsation frequency on heat transfer was measured using IR camera and heat flux-temperature micro foil sensor. The results obtained by both of these methods showed well agreement. Also, the results revealed significant influence of flow rate difference between steady and pulsating jet cases. In addition, the highest Nusselt number, Nu ≃ 7.2, was obtained at pulsation frequency of 20 Hz.

Fluid mechanical aspects of open- and closed-toe flue organ pipe voicing

2011 ◽  
Vol 2 (2) ◽  
pp. 284-295
Author(s):  
D. Steenbrugge
Keyword(s):  
Pressure Measurements ◽  
Jet Instability ◽  
Active Involvement ◽  
Air Jets ◽  
Air Jet ◽  
Hole Area ◽  
Power Regulation ◽  
Organ Pipes ◽  
Organ Pipe ◽  
Jet Characteristics

Open- and closed-toe voicing of flue organ pipes constitute two opposite extremes of possible ways todetermine the air-jet flow rate through the flue. The latter method offers more voicing control parametersand thus more flexibility, at the expense of a necessary pressure loss at the toe hole. Another differencebetween both cases arises from different air-jet characteristics, such as velocity profile, Re number, flowmomentum or aspect ratio, the latter influencing jet instability. Furthermore, for closed-toe voicing, the flowfield in the pipe foot is modified by an axisymmetric air jet created through the highly constricted toe hole.Velocity measurements on air jets, pressure measurements in the pipe foot are presented, compared anddiscussed for both voicing methods. The ratio of flue to toe hole area is shown to be the sole pipeparameter to entirely determine the jet velocity and can be useful to quantitatively characterize flue and toehole voicing. Open-toe voicing turns out to be the more delicate and low-pressure only method becauseany modification of the flue has consequences on all aspects of the pipe operation, whereas the closed-toemethod, in connection with higher pressures and with active involvement of cut-up adjustment, allows someseparation between sound timbre and power regulation.

Effects of Reacting Conditions on Flow Fields in a Swirl Stabilized Lean Premixed Can Combustor

2018 ◽  
Author(s):  
Suhyeon Park ◽  
Siddhartha Gadiraju ◽  
Jaideep Pandit ◽  
Srinath Ekkad ◽  
Federico Liberatore ◽  
...  
Keyword(s):  
Test Section ◽  
Atmospheric Condition ◽  
Jet Impingement ◽  
Swirl Flow ◽  
Reacting Flows ◽  
Flame Stabilization ◽  
Piv Measurements ◽  
Fuel Nozzle ◽  
Proper Orthogonal ◽  
The Impact

PIV measurements to understand the flow differences between reacting and non-reacting conditions were conducted in an optically accessible single can combustor. An industrial fuel nozzle was installed at the inlet of the test section to generate the swirl flow for flame stabilization and simulate realistic conditions of a gas turbine combustor. Five different equivalence ratios between 0.50 and 0.75 were tested with propane as fuel. Main air flow was also varied from Reynolds number from 50000 to 110000 with respect to the fuel nozzle diameter. Effect of preheating was tested by changing inlet air temperature from 23 to 200°C. The pressure at the test section was close to atmospheric condition throughout the tests. The measurements were performed with a 2-D PIV system. Time-averaged flow velocity, vorticity and turbulent kinetic energy (TKE) were obtained from PIV data and flow structures under different conditions were compared. Swirl jet impingement location on the liner wall was determined as well to understand the impact on the liner wall. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows.

Effect of Acoustic Feedback on Lagrangian Coherent Structures in a Backward Facing Step Combustor With a Partially Premixed Flame

2017 ◽  
Author(s):  
Ramgopal Sampath ◽  
S. R. Chakravarthy
Keyword(s):  
Coherent Structures ◽  
Large Scale ◽  
Pressure Oscillation ◽  
Velocity Fields ◽  
Premixed Flame ◽  
Time Resolved ◽  
Acoustic Feedback ◽  
Acoustic Characterization ◽  
Partially Premixed ◽  
Partially Premixed Flame

The thermoacoustic oscillations of a partially premixed flame stabilized in a backward facing step combustor are studied at a constant equivalence ratio in long and short combustor configurations corresponding to with and without acoustic feedback respectively. We perform simultaneous time-resolved particle image velocimetry (TR-PIV) and chemiluminescence for selected flow conditions based on the acoustic characterization in the long combustor. The acoustic characterization shows a transition in the dominant pressure amplitudes from low to high magnitudes with an increase in the inlet flow Reynolds number. This is accompanied by a shift in the dominant frequencies. For the intermittent pressure oscillations in the long combustor, the wavelet analysis indicates a switch between the acoustic and vortex modes with silent zones of relatively low-pressure amplitudes. The short combustor configuration indicates the presence of the vortex shedding frequency and an additional band comprising the Kelvin Helmholtz mode. Next, we apply the method of finite-time Lyapunov exponent (FTLE) to the time-resolved velocity fields to extract features of the Lagrangian coherent structures (LCS) of the flow. In the long combustor post transition with the time instants with dominant acoustic mode, a large-scale modulation of the FTLE boundaries over one cycle of pressure oscillation is evident. Further, the FTLEs and the flame boundaries align each other for all phases of the pressure oscillation. In the short combustor, the FTLEs indicate the presence of small wavelength waviness that overrides the large-scale vortex structure, which corresponds to the vortex shedding mode. This behaviour contrasts with the premixed flame in the short combustor reported earlier in which such large scales were found to be seldom present. The presence of the large-scale structures even in the absence of acoustic feedback in a partially premixed flame signifies its inherent unstable nature leading to large pressure amplitudes during acoustic feedback. Lastly, the FTLE boundaries provide the frequency information of the identified coherent structure and also acts as the surrogate flame boundaries that are estimated from just the velocity fields.

Modeling Unsteady Flow of a Lean Partially Premixed Flame on a Dry Low NOx Combustion System

2013 ◽  
Author(s):  
Salvatore Matarazzo ◽  
Hannes Laget ◽  
Evert Vanderhaegen ◽  
Jim B. W. Kok
Keyword(s):  
Gas Turbine ◽  
Limit Cycle ◽  
Gas Turbines ◽  
Premixed Flame ◽  
Computational Domain ◽  
Pressure Oscillations ◽  
Combustion Dynamics ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
Limit Cycle Behavior

The phenomenon of combustion dynamics (CD) is one of the most important operational challenges facing the gas turbine (GT) industry today. The Limousine project, a Marie Curie Initial Training network funded by the European Commission, focuses on the understanding of the limit cycle behavior of unstable pressure oscillations in gas turbines, and on the resulting mechanical vibrations and materials fatigue. In the framework of this project, a full transient CFD analysis for a Dry Low NOx combustor in a heavy duty gas turbine has been performed. The goal is to gain insight on the thermo-acoustic instability development mechanisms and limit cycle oscillations. The possibility to use numerical codes for complex industrial cases involving fuel staging, fluid-structure interaction, fuel quality variation and flexible operations has been also addressed. The unsteady U-RANS approach used to describe the high-swirled lean partially premixed flame is presented and the results on the flow characteristics as vortex core generation, vortex shedding, flame pulsation are commented on with respect to monitored parameters during operations of the GT units at Electrabel/GDF-SUEZ sites. The time domain pressure oscillations show limit cycle behavior. By means of Fourier analysis, the coupling frequencies caused by the thermo-acoustic feedback between the acoustic resonances of the chamber and the flame heat release has been detected. The possibility to reduce the computational domain to speed up computations, as done in other works in literature, has been investigated.

scholarly journals Experimental testing of exterior wall mounted mechanical ventilation exhaust air outlet devices

2021 ◽  
Vol 246 ◽  
pp. 02001
Author(s):  
Ülar Palmiste ◽  
Tauno Meier ◽  
Jarek Kurnitski ◽  
Hendrik Voll
Keyword(s):  
Mechanical Ventilation ◽  
Experimental Testing ◽  
Airflow Rate ◽  
Tracer Gas ◽  
Qualitative Comparison ◽  
Smoke Visualization ◽  
Air Jets ◽  
Air Jet ◽  
Building Wall ◽  
Face Velocity

The purpose of the study was to experimentally test the performance of four types of wall-mounted mechanical ventilation exhaust air outlet devices. A full-scale mock-up of a segment of an external wall with an exhaust air outlet was constructed. The tested exhaust air devices include a gravity louver, fixed-blade louver, louver plate, and exhaust nozzle. The performance assessment included two types of experiments over the exhaust airflow rate range of 25–94 l/s at isothermal conditions with no influencing wind: (i) the particle tracer method with smoke to visualize the exhaust air jets from the outlets, and (ii) the tracer gas method to measure the dilution of CO2 concentration in the exhaust air jet. Furthermore, the aerodynamic performance was comparatively evaluated in terms of pressure drop and exhaust air face velocity at the outlet. The qualitative comparison of airflow patterns by smoke visualization showed notable differences between the tested device types. Concentration decrease evaluation indicated that the exhaust air pollutants are more efficiently transported away from the building wall by exhaust outlets that discharge at 0–45 degrees downwards from the horizontal plane. Discharge angles 60–90 degrees downwards produced a wall-attached jet and the pollutant tracer concentration remained relatively high in the vicinity of the wall.

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