Effects of Flame Lift-Off on the Differences Between the Diffusion Flames From Circular and Elliptic Burners

1998 ◽  
Vol 120 (2) ◽  
pp. 161-166 ◽  
Author(s):  
S. R. Gollahalli
Keyword(s):  
Experimental Study ◽  
Combustion Product ◽  
Axial Velocity ◽  
Diffusion Flames ◽  
Air Entrainment ◽  
Lifted Flames ◽  
The Mean ◽  
Lift Off ◽  
Product Species

An experimental study conducted to determine the effects of lifting the flame base off the burner rim on the differences between the flame characteristics of diffusion flames from circular and elliptic burners is presented. The in-flame profiles of temperature, concentrations of fuel and combustion product species, and the mean and fluctuating components of axial velocity are presented. This study has shown that the effects of burner geometry in turbulent lifted flames are considerable only in the near-burner region. In the midflame and far-burner regions, the effects traceable to burner geometry are much weaker, contrary to those observed in the attached flame configuration. The observations are attributed to the turbulence and additional air entrainment into the jet prior to the flame base accompanying the lift-off process, which mitigate the effects of burner geometry.

Investigation of Extinction and Reignition Events Using the Flamelet Generated Manifold Model

2018 ◽  
Author(s):  
Hossam Elasrag ◽  
Shaoping Li
Keyword(s):  
Boundary Layer ◽  
Axial Velocity ◽  
Bluff Body ◽  
Grid Turbulence ◽  
Eddy Simulation ◽  
Flamelet Generated Manifold ◽  
Spray Droplets ◽  
The Mean ◽  
Lift Off ◽  
Flame Brush

Simulations for the Cambridge swirl bluff-body spray burner are performed near blow-out conditions. A hybrid stress blended eddy simulation (SBES) model is utilized for sub-grid turbulence closure. SBES blends the RANS-SST model at the boundary layer with large eddy simulation dynamic Smagorinsky model outside the boundary layer. The injected N-heptane spray droplets are tracked using a typical Eulerian-Lagrangian approach. Heat transfer coupling between the bluff-body walls and the near-walls fluid is accounted for by coupling the solid and fluid energy equations at the bluff-body surface. Mixing and chemistry are modeled using the Flamelet Generated Manifold (FGM) model. The study investigates how successful the FGM model is in predicting finite rate effects like local extinction and flame lift-off height. To this end, two near blow-out spray flames, the H1S1 (75% to blow-out) and H1S2 (88% to blow-out) are simulated. Good results are shown matching the spray Sauter mean diameter (SMD) and axial velocity mean and rms experimental data. The results also show that the FGM model captured reasonably well the flame structure and lift-off height as well as the spray pattern. Overall the spray droplets mean D32 and mean axial velocity were under-predicted, while the rms distribution matched reasonably well for the H1S1 flame. The mean flame brush lift-off height is estimated based on the statistically stationary mean flame brush and is estimated to be around 6 mm from the bluff-body base. Instantaneous local flame extinction is observed. The H1S2 flame, however, showed similar but slightly better match with the measurements for the mean spray data compared to the H1S1 flame, with slight under-prediction for D32 at Z = 10 mm and Z = 20 mm. Future work will investigate the sensitivity of the simulation to the spray boundary conditions and grid resolution.

Control of cavity tones using a spanwise cylinder

2008 ◽  
Vol 86 (12) ◽  
pp. 1355-1365 ◽  
Author(s):  
L Keirsbulck ◽  
M El Hassan ◽  
M Lippert ◽  
L Labraga
Keyword(s):  
Experimental Study ◽  
Shear Layer ◽  
Layer Thickness ◽  
Axial Velocity ◽  
High Frequency ◽  
Sound Pressure ◽  
Leading Edge ◽  
Deep Cavity ◽  
Change In The Mean ◽  
The Mean

A detailed experimental study of flow over a deep cavity was conducted towards understanding the attenuation of tones using a spanwise cylinder. Two “no-control” cavities were compared with a similar configuration using a cylinder on the leading edge of the cavities. Parametric changes of the spanwise cylinder such as the distance from the wall are studied. Maximum control across the range of studied velocities occurs for a particular position of the spanwise cylinder for the two configurations. Reductions in sound pressure levels (SPL) of up to 36 dB were obtained. Moreover, a shaped cylinder was also studied and shows that the attenuation of tones is not due to high-frequency pulsing as suggested in the literature, but to an increase of the cavity-shear-layer thickness due to the change in the mean axial velocity profiles.PACS Nos.: 47.27.Rc, 47.27.Sd

Pressure Dependence of the Stability Limits and the NOX Exhaust Gas Concentrations in Case of Swirl-Stabilized, Diffusion Flames Burning in a Lift-Off Regime

2009 ◽  
Author(s):  
Plamen Kasabov ◽  
Nikolaos Zarzalis
Keyword(s):  
Reaction Zone ◽  
Diffusion Flames ◽  
Sudden Change ◽  
Measurement Data ◽  
Exhaust Gas ◽  
Stabilization Mechanism ◽  
Lifted Flames ◽  
Lift Off ◽  
Stability Limits ◽  
The Impact

The present study deals with confined, swirl-stabilized, diffusion flames burning in a lift-off regime and is meant to be a meaningful extension of our previous work [1]. The unique features of these hybrid flames originate from the presence of the so called lift-off zone located between the burner exit and the reaction zone. In the lift-off zone, surrounded by hot recirculating exhaust gases, the liquid fuel heats up and will reach a certain degree of prevaporation and premixing before entering the reaction zone. For that reason lifted flames posses some of the advantages of the premixed flames, for example in respect of emissions, but lack their major drawbacks, such as susceptibility to flashback and combustion noise. The investigations were motivated by the high NOX reduction potential of the lifted flames and the scarce information about their emission characteristics, flame behaviour and stability limits for gas turbine typical conditions especially when operated with liquid fuels. In order to gain a deeper understanding of the stabilization mechanism of lifted flames, several process parameters were varied within this study. The impact of the pressure (up to 18bar), of the air preheating and of the stoichiometry on the NOX emissions and on the lean blowout limits was investigated and discussed. The lift-off burning mode was achieved by utilizing a modified airblast nozzle and kerosene serving as a fuel. To acquire measurement data for a set of Reynolds numbers and residence times, four nozzles with similar geometries, but different scaling factors were employed. All main components of the exhaust gas were detected by means of conventional gas analysis. The NOX concentrations for the whole measured pressure range and for adiabatic flame temperatures up to 1800K does not exceed 20ppm normalized for 15% O2. The carbon monoxide concentration served as indicator for the presence of flame instabilities. The evaluation of the gathered data revealed some interesting phenomena. For example a sudden change in the nitrogen oxides concentration plotted over the equivalence ratio allows to distinguish between two burning modes: lift-off and detached flame. Another interesting finding is a maximum in the profile of the LBO limits as a function of the operational pressure, signifying a change in the predominant stabilization mechanism.

Lift-Off, Reattachment and Blowout Limits of Co-Flow Jet Diffusion Flames

2002 ◽  
Author(s):  
M. Karbasi ◽  
I. Wierzba
Keyword(s):  
Diffusion Flames ◽  
Flame Stabilization ◽  
Nozzle Geometry ◽  
Stream Velocity ◽  
Jet Diffusion Flames ◽  
Air Stream ◽  
Lifted Flames ◽  
Lift Off ◽  
The Stability ◽  
Flowing Stream

The stability behaviour of jet diffusion flames in a co-flowing stream of air was examined. Their lift-off, reattachment and blowout limits were established for methane, propane, ethylene and hydrogen. The co-flowing air stream velocity affected significantly the mechanism of flame stabilization. Different flow regimes where the blowout of lifted flames or attached flames can occur were recognized. A transition region in which both the blowout of lifted flames as well as that of attached flames was observed and identified with respect to the value of the air stream velocity. It was found that the blowout limits for lifted flames in this region were much smaller than for the attached flames. The effects of changes in the nozzle geometry and co-flowing stream composition were also considered.

The experimental study of flame height and lift-off height of propane diffusion flames diluted by carbon dioxide

Fuel ◽  
2021 ◽  
Vol 290 ◽  
pp. 119958
Author(s):  
Changfa Tao ◽  
Bin Liu ◽  
Yuling Dou ◽  
Yejian Qian ◽  
Yu Zhang ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Experimental Study ◽  
Diffusion Flames ◽  
Flame Height ◽  
Lift Off

Non-buoyant diffusion flames with oscillatory air entrainment

1997 ◽  
Author(s):  
U. Hegde ◽  
D. Stocker ◽  
M. Bahadori ◽  
D. Stocker ◽  
M. Bahadori ◽  
...  
Keyword(s):  
Diffusion Flames ◽  
Air Entrainment ◽  
Buoyant Diffusion Flames

scholarly journals Experimental study on the mean flow characteristics of a supersonic multiple jet configuration

2021 ◽  
Vol 108 ◽  
pp. 106377
Author(s):  
Mohammed Faheem ◽  
Aqib Khan ◽  
Rakesh Kumar ◽  
Sher Afghan Khan ◽  
Waqar Asrar ◽  
...  
Keyword(s):  
Experimental Study ◽  
Flow Characteristics ◽  
Mean Flow ◽  
The Mean

Effects of finite-rate chemistry and detailed transport on the instability of jet diffusion flames

2014 ◽  
Vol 745 ◽  
pp. 647-681 ◽  
Author(s):  
Yee Chee See ◽  
Matthias Ihme
Keyword(s):  
Transport Properties ◽  
Diffusion Flames ◽  
Diffusive Transport ◽  
Mean Flow ◽  
Stability Behaviour ◽  
Jet Diffusion Flames ◽  
One Step ◽  
The Mean ◽  
Modelling Assumptions ◽  
The Stability

AbstractLocal linear stability analysis has been shown to provide valuable information about the response of jet diffusion flames to flow-field perturbations. However, this analysis commonly relies on several modelling assumptions about the mean flow prescription, the thermo-viscous-diffusive transport properties, and the complexity and representation of the chemical reaction mechanisms. In this work, the effects of these modelling assumptions on the stability behaviour of a jet diffusion flame are systematically investigated. A flamelet formulation is combined with linear stability theory to fully account for the effects of complex transport properties and the detailed reaction chemistry on the perturbation dynamics. The model is applied to a methane–air jet diffusion flame that was experimentally investigated by Füriet al.(Proc. Combust. Inst., vol. 29, 2002, pp. 1653–1661). Detailed simulations are performed to obtain mean flow quantities, about which the stability analysis is performed. Simulation results show that the growth rate of the inviscid instability mode is insensitive to the representation of the transport properties at low frequencies, and exhibits a stronger dependence on the mean flow representation. The effects of the complexity of the reaction chemistry on the stability behaviour are investigated in the context of an adiabatic jet flame configuration. Comparisons with a detailed chemical-kinetics model show that the use of a one-step chemistry representation in combination with a simplified viscous-diffusive transport model can affect the mean flow representation and heat release location, thereby modifying the instability behaviour. This is attributed to the shift in the flame structure predicted by the one-step chemistry model, and is further exacerbated by the representation of the transport properties. A pinch-point analysis is performed to investigate the stability behaviour; it is shown that the shear-layer instability is convectively unstable, while the outer buoyancy-driven instability mode transitions from absolutely to convectively unstable in the nozzle near field, and this transition point is dependent on the Froude number.

Quasi-Experimental study of effects of lighting on rest, activity and melatonin in postpartum women

2021 ◽  
Vol 74 (6) ◽  
Author(s):  
Cristina Furtado Volcov ◽  
Eliana Moreira Pinheiro ◽  
Miriam Harumi Tsunemi ◽  
Fernanda Gaspar do Amaral ◽  
Ariane Ferreira Machado Avelar ◽  
...  
Keyword(s):  
Experimental Study ◽  
Comparison Group ◽  
Total Load ◽  
Long Wavelength ◽  
Light Regimen ◽  
Early Postpartum ◽  
Comparison Groups ◽  
Quasi Experimental ◽  
The Mean ◽  
Experimental Group

ABSTRACT Objectives: to compare the parameters of the activity/rest cycle of early postpartum breastfeeding women under a controlled and uncontrolled long wavelength ray light regimen. Methods: quasi-experimental study with breastfeeding women and their babies during postnatal rooming-in, São Paulo, Brazil. Participants were allocated to either an experimental (intervention) or a comparison group. The intervention involved exposure of the woman in a controlled room with artificial long wavelength ray light at night. Each woman’s level of 6-sulfatoxymelatonin at 24 hours and activity/rest times was analyzed. Results: the mean activity/rest times of women in the experimental and comparison groups were similar. The mean percentages of total load of 6-sulfatoxymelatonin during the day and night were similar (p=0.09). At 24 hours, the experimental group presented a significantly lower mean percentage of total load compared to the comparison group (p=0.04). Conclusions: women who stayed in the room with long-wavelength artificial light showed no difference in activity/rest and 6-sulfatoxymelatonin levels in the early postpartum period.

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