scholarly journals Experimental study of confined coaxial jets in a non-axisymmetric co-flow

2020 ◽  
Vol 61 (12) ◽  
Author(s):  
I. A. Sofia Larsson ◽  
Henrik Lycksam ◽  
T. Staffan Lundström ◽  
B. Daniel Marjavaara
Keyword(s):  
Combustion Process ◽  
Flame Length ◽  
Mixing Process ◽  
Flowing Fluid ◽  
Complete Combustion ◽  
Coaxial Jets ◽  
Planar Laser ◽  
Jet Behavior ◽  
Low Mass ◽  
Secondary Fluid

Abstract Confined, turbulent, coaxial jets in a non-axisymmetric co-flow are studied using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) simultaneously. Eight different cases are measured. Two momentum flow ratios of the co-flow are used in the experiment to investigate the effect on the coaxial burner jet behavior and mixing characteristics of the coaxial jet flow and the co-flowing, secondary fluid. In addition, four different momentum flow ratios of the coaxial outer to inner jet are investigated. The objective of the study is to get a deeper understanding of how the flow dynamics affects the entrainment and mixing process in a coaxial jet with a non-axisymmetric, surrounding co-flow. The results show that the introduction of a coaxial stream affects the inner jet and decreases the mixing with the surrounding co-flow; the effect is enhanced as the momentum flow ratio of the coaxial jet increases. The distribution of the secondary, co-flowing fluid controls the shape and direction of the coaxial jet, but does not have a significant impact on the mixing process near the centerline. Practical implications of this investigation are related to the possibility to better control a diffusion flame by introducing a coaxial stream. In this context it is concluded that it is possible to affect the jet development and hence the flame length. The conclusion is based on the assumption that the outer, coaxial stream has a low mass flow, not enough to provide complete combustion, and hence the co-flowing, secondary fluid provides the air needed for the combustion process. Graphic abstract

scholarly journals Study on the Combustion Process of Premixed Methane Flames with CO2 Dilution at Elevated Pressures

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 348 ◽  
Author(s):  
Rafał Ślefarski
Keyword(s):  
Thermal Dissociation ◽  
Combustion Process ◽  
Elevated Pressure ◽  
Flame Length ◽  
Nox Emission ◽  
Atmospheric Conditions ◽  
Elevated Pressures ◽  
Wide Range ◽  
Planar Laser ◽  
Methane Flames

The article presents the results of experimental and numerical investigation of turbulent premixed methane flames diluted by carbon dioxide (up to 30%) at atmospheric and elevated pressures (up to 0.5 MPa). The study included the influence of fuel properties and operation parameters on the emission of NOx and CO as well as flame properties. The investigation has been prepared for two combustion system configurations (axisymmetric flames and flames supported by a pilot flame) in a wide range of air/fuel equivalence ratios (ϕ = 0.42 ÷ 0.85). It has been reported that reduction of NOx emission by CO2 fuel dilution reached a level of up to 45% in atmospheric conditions and 30% at elevated pressure, decreasing with a drop in the equivalence ratio. The results have shown influence of pressure on NOx composition, where for pressurized tests, NO2 was doubled compared to atmospheric tests. Carbon monoxide emission rises with CO2 content in the fuel as a result of thermal dissociation, but this phenomenon is mitigated by a pressure increase. Planar laser induced fluorescence (PLIF) study has shown that flame length decreases with an increase in pressure and CO2 content in the fuel. Fuel staging increased NOx emission, especially for richer flames (ϕ > 0.6) at low pressure, while CO increased in the whole range of equivalence ratios.

scholarly journals The Evolution of 3He, 4He and D in the Galaxy

2000 ◽  
Vol 198 ◽  
pp. 540-546 ◽  
Author(s):  
Cristina Chiappini ◽  
Francesca Matteucci
Keyword(s):  
Chemical Evolution ◽  
Present Model ◽  
Galactic Disk ◽  
The Sun ◽  
Mixing Process ◽  
Low Mass Stars ◽  
A Value ◽  
The Galaxy ◽  
Low Mass ◽  
Standing Problem

In this work we present the predictions of a modified version of the ‘two-infall model’ (Chiappini et al. 1997 - CMG) for the evolution of 3He, 4He and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M⊙), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of 3He by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)p < 3 × 10—5 is suggested by the present model. Finally, adopting the primordial 4He abundance suggested by Viegas et al. (1999), we obtain a value for ΔY/ΔZ ≃ 2 and a better agreement with the solar 4He abundance.

scholarly journals Li Enrichment, Mass Loss, and CN Abundances in High Rotating K Giants

2004 ◽  
Vol 215 ◽  
pp. 242-243
Author(s):  
N. A. Drake ◽  
R. de la Reza ◽  
L. da Silva ◽  
D. L. Lambert
Keyword(s):  
Mass Loss ◽  
Spectral Resolution ◽  
High Spectral Resolution ◽  
Mixing Process ◽  
Stellar Activity ◽  
New Models ◽  
Low Mass ◽  
K Giants

High rotating low-mass K giants can be considered as interesting new “laboratories” for studies of the mixing process and mass loss. By means of high spectral resolution observations of some rapidly rotating K giants we found a series of connections between rotation, stellar activity, high Li abundance and mass loss. These giants show low 14N and high 13C enrichment. Nearly half of them are Li rich. This frequency is much higher than the ~ 2% corresponding to common, low rotating K giants. They are also the most suitable objects to test new models of rotation-induced mixing or planet engulfing scenarios.

Use of Ceramic Injection Molding Technology to Increase Biogas Burners Efficiency

2017 ◽  
Vol 736 ◽  
pp. 127-131 ◽  
Author(s):  
V.Y. Sokolov ◽  
S.A. Naumov ◽  
A.V. Sadchikov ◽  
S.V. Mitrofanov
Keyword(s):  
Injection Molding ◽  
High Efficiency ◽  
Combustion Process ◽  
Gas Mixture ◽  
Complete Combustion ◽  
Ceramic Injection Molding

The article gives considerations to issues relating to organization of biogas combustion process. A new design of biogas burner is suggested. It differs from existing analogues by more complete combustion of air and gas mixture and high efficiency. Feasibility of greater burners' effectiveness due to the use of ceramic injection molding technology is demonstrated here.

Process Heater Air Infiltration

2010 ◽  
Author(s):  
Charles E. Baukal ◽  
Wesley R. Bussman
Keyword(s):  
Flame Length ◽  
Excess Oxygen ◽  
Oxygen Level ◽  
Heat Flux Distribution ◽  
Complete Combustion ◽  
Gaseous Fuels ◽  
Air Leaks ◽  
Air Infiltration ◽  
Pollution Emissions ◽  
The Impact

Process heaters are among the largest energy consumers in industry. Many of them were built years ago and often are not well sealed which leads to excessive air infiltration. Air leaks may be caused by cracks in the wall, by sight ports that are not properly sealed or may even be left open, failure to close air registers for burners that are out of service, improper sealing of penetrations through the heater walls, and by excessive draft levels in the heater. These leaks reduce energy efficiency and indirectly increase pollution emissions as more fuel must be consumed for a given production rate. Leaks may also directly cause NOx emissions to increase due to increased excess oxygen. Excessive air leakage can indirectly cause process burners to operate improperly. The excess oxygen level in a heater is normally controlled to a certain target value, typically about 2–3% by volume for gaseous fuels. Process burners are designed assuming that all of the air for combustion goes through the burner. However, if a significant amount of air is leaking into a heater, the measured excess oxygen level may be on target but not enough of the air is coming through the burner which can adversely affect performance. The flame length may be dramatically increased as the flame searches for air to complete combustion which often causes flame impingement on process tubes. The heat flux distribution may be shifted as the flame length increases. The flames may even become unstable if they are sufficiently starved for air. The draft level in a heater varies with elevation which means that air infiltration depends not only on the size of the leak opening, but also on its location. This paper will include an analysis of how excess air infiltration affects thermal efficiency and how the location of the leak and the heater draft level affect the amount of air infiltration. The impact of air infiltration on burner performance will be discussed. Techniques will be recommended for detecting air leaks and how to correct them.

scholarly journals Performance of a Reduced NOx Diffusion Flame Combustor for the MS5002 Gas Turbine

1999 ◽  
Author(s):  
Alan S. Feitelberg ◽  
Michael D. Starkey ◽  
Richard B. Schiefer ◽  
Roointon E. Pavri ◽  
Matt Bender ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Diffusion Flame ◽  
Turbulent Flame ◽  
Flame Length ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
British Petroleum ◽  
Complete Combustion ◽  
Significant Difference ◽  
Fuel Nozzle

This paper describes a reduced NOx diffusion flame combustor that has been developed for the MS5002 gas turbine. Laboratory tests have shown that when firing with natural gas, without water or steam injection, NOx emissions from the new combustor are about 40% lower than NOx emissions from the standard MS5002 combustor. CO emissions are virtually unchanged at base load, but increase at part load conditions. The laboratory results were confirmed in 1997 by a commercial demonstration test at a British Petroleum site in Prudhoe Bay, Alaska. The standard MS5002 gas turbine is equipped with a conventional, swirl stabilized diffusion flame combustion system. The twelve standard combustors in an MS5002 turbine are cylindrical cans, approximately 27 cm (10.5 inches) in diameter and 112 cm (44 inches) long. A small, annular, vortex generator surrounds the single fuel nozzle that is centered at the inlet to each can. The walls of the cans are louvered for cooling, and contain an array of mixing and dilution holes that provide the air needed to complete combustion and dilute the burned gas to the desired turbine inlet temperature. The new, reduced NOx emissions combustor (referred to as a “lean head end”, or LHE, combustor) retains all of the key features of the conventional combustor: the only significant difference is the arrangement of the mixing and dilution holes in the cylindrical combustor can. By optimizing the number, diameter, and location of these holes, NOx emissions were substantially reduced. The materials of construction, fuel nozzle, and total combustor air flow were unchanged. The differences in NOx emissions between the standard and LHE combustors, as well as the variations in NOx emissions with firing temperature, were well correlated using turbulent flame length arguments. Details of this correlation are also presented.

Controlling Gravity Impact on Diffusion Flames by Magnetic Field

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Fouad Khaldi
Keyword(s):  
Magnetic Field ◽  
Scaling Laws ◽  
Diffusion Flames ◽  
Combustion Process ◽  
Flame Length ◽  
Dimensionless Number ◽  
Length Variation ◽  
Zero Gravity ◽  
Blue Color ◽  
Gravity Level

The ability to use a magnetic field as a means for controlling the role of gravity buoyancy on the combustion process is demonstrated by applying a strong vertical magnetic field gradient on a laminar gas jet diffusion flame. The confirmation is based on a comparison of flame appearance; in particular, length variation, to both elevated gravity (higher than earth’s gravity) and zero-gravity combustion experimental data. The comparison parameter is the dimensionless number G, defined as the ratio of gravity level generated by magneto-gravity buoyancy to earth’s gravity. The more important results are as follows. First, for G > 1, good agreement between magnetic and centrifuge length scaling laws reveals that the slight decrease of flame length according to L ∼ G−1/8 is the result of increasing artificial magnetically induced gravity strength. It ensues that flame thinning, bluing, lifting, and extinction are produced by similar mechanisms previously identified in centrifuge diffusion flames. Thereafter, at G ≅ 0, the flame assumes a nearly hemispheric shape and a blue color in perfect similarity to nonbuoyant flames under zero-gravity conditions generated in drop towers. Another important fact is that the magnetic field offers the ability to observe the flame behavior at low gravity levels 0 < G < 1. A primary interesting result is that flame length varies strongly, following the scaling law L ∼ G−1/2.

Planar Imaging of Vortex Dynamics in Flames

1989 ◽  
Vol 111 (1) ◽  
pp. 148-155 ◽  
Author(s):  
E. Gutmark ◽  
T. P. Parr ◽  
D. M. Parr ◽  
K. C. Schadow
Keyword(s):  
Fluid Dynamics ◽  
Shear Layer ◽  
Large Scale ◽  
Combustion Process ◽  
Oh Radical ◽  
Planar Imaging ◽  
Reaction Parameters ◽  
Large Scale Structures ◽  
Planar Laser ◽  
Scale Structures

The interaction between the fluid dynamics and the combustion process in an annular diffusion flame was studied experimentally using the Planar Laser Induced Fluorescence (PLIF) technique. The local temperature and OH radical fluorescence signals were mapped in the entire flame cross section. The flame was forced at different instability frequencies, thus enabling the study of the evolution and interaction of large-scale structures in the flame shear layer. The present study of the effect of fluid dynamics on combustion is part of a more comprehensive program aimed at understanding and controlling the effect of heat release, density variations, and reaction parameters on the shear layer evolution.

Numerical Simulation of Combustion Process in a 350t/d MSW Incinerator

2012 ◽  
Vol 268-270 ◽  
pp. 898-901
Author(s):  
Shui E Yin ◽  
Jun Wu
Keyword(s):  
Numerical Simulation ◽  
Mathematical Model ◽  
Combustion Process ◽  
Species Distributions ◽  
Complete Combustion ◽  
Operational Conditions ◽  
Furnace Outlet ◽  
Air Supply ◽  
Total Temperature ◽  
Secondary Air

A mathematical model was presented for the combustion of municipal solid waste in a 350t/d MSW-burning incinerator. Numerical simulations were performed to predict the temperature and the species distributions in the furnace, with practical operational conditions taken into account. When the total air supply is constant, reducing primary air and increasing secondary air properly results in the higher total temperature of the furnace and the more oxygen concentration at the furnace outlet, and thereby contributes to the complete combustion of combustibles so that an optimal combustion effect can be achieved.

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