Effects of Diluents on Lifted Turbulent Methane and Ethylene Jet Flames

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Andrew R. Hutchins ◽  
James D. Kribs ◽  
Kevin M. Lyons
Keyword(s):  
Mole Fraction ◽  
Flame Speed ◽  
Flow Conditions ◽  
Jet Flames ◽  
Nitrogen Dilution ◽  
Potential Impact ◽  
Methane Flames ◽  
Burner Operation ◽  
Jet Velocities ◽  
Ethylene Flames

The effects of diluents on the liftoff of turbulent, partially premixed methane and ethylene jet flames for potential impact in industrial burner operation for multifuel operation have been investigated. Both fuel jets were diluted with nitrogen and argon in separate experiments, and the flame liftoff heights were compared for a variety of flow conditions. Methane flames have been shown to liftoff at lower jet velocities and reach blowout conditions much more rapidly than ethylene flames. Diluting ethylene and methane jets with nitrogen and argon, independently, resulted in varying trends for each fuel. At low dilution levels (∼5% by mole fraction), methane flames were lifted to similar heights, regardless of the diluent type; however, at higher dilution levels (∼10% by mole fraction) the argon diluent produced a flame which stabilized farther downstream. Ethylene jet flames proved to vary less in liftoff heights with respect to diluent type. Significant soot reduction with dilution is witnessed for both ethylene and methane flames, in that flame luminosity alteration occurs at the flame base at increasing levels of argon and nitrogen dilution. The increasing dilution levels also decreased the liftoff velocity of the fuel. Analysis showed little variance among liftoff heights in ethylene flames for the various inert diluents, while methane flames proved to be more sensitive to diluent type. This sensitivity is attributed to the more narrow limits of flammability of methane in comparison to ethylene, as well as the much higher flame speed of ethylene flames.

Experimental Observations of Nitrogen Diluted Ethylene and Methane Jet Flames

2013 ◽  
Author(s):  
Andrew R. Hutchins ◽  
James D. Kribs ◽  
Richard D. Muncey ◽  
William A. Reach ◽  
Kevin M. Lyons
Keyword(s):  
Thermal Diffusivity ◽  
Higher Order ◽  
Flame Stabilization ◽  
Hydrocarbon Fuels ◽  
Jet Flames ◽  
Nitrogen Dilution ◽  
Fuel Mixtures ◽  
And Behavior ◽  
Ethylene Flames

While the liftoff mechanisms of nitrogen-diluted methane jet flames have been well documented, higher order fuels, such as ethylene, have not been studied as extensively with regards to flame stabilization and behavior. Higher order fuels generally burn more intensely, and thus produce much different stabilization patterns than those of simple hydrocarbon fuels, such as methane. The purpose of this study was to observe the effects of nitrogen dilution on ethylene combustion and compare to that witnessed in typical methane jet flames; specifically, the influence on the liftoff height, blowout, and flame chemiluminescence. Liftoff and blowout velocities were compared for various mixtures of ethylene without nitrogen. It was observed that the reason behind the varying stabilization patterns is due to the higher thermal diffusivity of ethylene as well the higher flame speeds that are characterized in the combustion of ethylene. Using a sequence of images from each mixture, the flame liftoff heights were recorded. Due to the strong chemiluminescence of ethylene flames, little fluctuation between liftoff parameters was observed, with respect the velocity; however, there was a significant effect on the liftoff height, with respect to dilution. Blowout for fuel mixtures was much more difficult to achieve due to the higher thermal diffusivity of ethylene, meaning the flame would stabilize at positions much farther downstream than those of simple hydrocarbon fuels.

The Influence of Singlet Oxygen and Ozone on the Combustion in Methane-Air Mixture

2013 ◽  
Vol 699 ◽  
pp. 111-118
Author(s):  
Rui Shi ◽  
Chang Hui Wang ◽  
Yan Nan Chang
Keyword(s):  
Singlet Oxygen ◽  
Chemical Kinetics ◽  
Mole Fraction ◽  
Ignition Delay ◽  
Delay Time ◽  
Ignition Delay Time ◽  
Laminar Flame ◽  
Combustion Products ◽  
Flame Speed ◽  
Air Mixing

Based on GRI3.0, we study the main chemical kinetics process about reactions of singlet oxygen O2(a1Δg) and ozone O3 with methane-air combustion products, inherit and further develop research in chemical kinetics process with enhancement effects on methane-air mixed combustion by these two molecules. In addition, influence of these two molecules on ignition delay time and flame speed of laminar mixture are considered in our numerical simulation research. This study validates the calculation of this model which cotains these two active molecules by using experimental data of ignition delay time and the speed of laminar flame propagation. In CH4-air mixing laminar combustion under fuel-lean condition(ф=0.5), flame speed will be increased, and singlet oxygen with 10% of mole fraction increases it by 80.34%, while ozone with 10% mole fraction increase it by 127.96%. It mainly because active atoms and groups(O, H, OH, CH3, CH2O, CH3O, etc) will be increased a lot after adding active molecules in the initial stage, and chain reaction be reacted greatly, inducing shortening of reaction time and accelerating of flame speed. Under fuel rich(ф=1.5), accelerating of flame speed will be weakened slightly, singlet oxygen with 10% in molecular oxygen increase it by 48.93%, while ozone with 10% increase it by 70.25%.

Nitrogen-Diluted Methane Flames in the Near-and Far-Field

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
James Kribs ◽  
Nancy Moore ◽  
Tamir Hasan ◽  
Kevin Lyons
Keyword(s):  
Reynolds Number ◽  
Natural Gas ◽  
Low Reynolds Number ◽  
Industrial Applications ◽  
Flame Height ◽  
Far Field ◽  
Jet Flames ◽  
Jet Flame ◽  
Lifted Flame ◽  
Nitrogen Dilution

With the increased utilization of multicomponent fuels, such as natural gas and biogas, in industrial applications, there is a need to be able to effectively model and predict the properties of jet flames for mixed fuels. In addition, the interaction of these diluted fuels with outside influences (such as differing levels of coflow air) is a primary consideration. Experiments were performed on methane jet flames under the influence of varying levels of nitrogen dilution, from low Reynolds number lifted regimes to blowout, observing the influence of the nitrogen on lifted flame height and flame chemiluminesence images. These findings were analyzed and compared with existing lifted jet flame relations, such as the flammable region approximation proposed by Tieszen et al., as well as to undiluted flames. The influence of nitrogen dilution was seen to have an effect on the liftoff height of the flame, as well as the blowout velocity of the flame, but was seen to have a less pronounced effect compared with flames with coflowing air.

Boundary Layer Flashback Prediction for Turbulent Premixed Jet Flames: Comparison of Two Models

2019 ◽  
Author(s):  
Alireza Kalantari ◽  
Nicolas Auwaijan ◽  
Vincent McDonell
Keyword(s):  
Boundary Layer ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Operating Conditions ◽  
Pollutant Emissions ◽  
Jet Flames ◽  
Turbulent Flame Speed ◽  
Turbulent Premixed

Abstract Lean-premixed combustion is commonly used in gas turbines to achieve low pollutant emissions, in particular nitrogen oxides. But use of hydrogen-rich fuels in premixed systems can potentially lead to flashback. Adding significant amounts of hydrogen to fuel mixtures substantially impacts the operating range of the combustor. Hence, to incorporate high hydrogen content fuels into gas turbine power generation systems, flashback limits need to be determined at relevant conditions. The present work compares two boundary layer flashback prediction methods developed for turbulent premixed jet flames. The Damköhler model was developed at University of California Irvine (UCI) and evaluated against flashback data from literature including actual engines. The second model was developed at Paul Scherrer Institut (PSI) using data obtained at gas turbine premixer conditions and is based on turbulent flame speed. Despite different overall approaches used, both models characterize flashback in terms of similar parameters. The Damköhler model takes into account the effect of thermal coupling and predicts flashback limits within a reasonable range. But the turbulent flame speed model provides a good agreement for a cooled burner, but shows less agreement for uncooled burner conditions. The impact of hydrogen addition (0 to 100% by volume) to methane or carbon monoxide is also investigated at different operating conditions and flashback prediction trends are consistent with the existing data at atmospheric pressure.

Velocity Profiles in Stenosed Tube Models Using Magnetic Resonance Imaging

1988 ◽  
Vol 110 (3) ◽  
pp. 180-184 ◽  
Author(s):  
S. E. Rittgers ◽  
Ding-yu Fei ◽  
K. A. Kraft ◽  
P. P. Fatouros ◽  
P. R. S. Kishore
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Laminar Flow ◽  
Measurement Technique ◽  
Turbulent Jets ◽  
Tube Model ◽  
Resonance Imaging ◽  
Flow Conditions ◽  
Jet Velocities ◽  
Termination Point

A time-of-flight MRI velocity measurement technique is evaluated against corresponding LDV measurements in a constriction tube model over a range of physiologic flow conditions. Results from this study show that MR displacement images can: 1) be obtained within both laminar and turbulent jets (maximum stenotic Re≅4,200), 2) measure mean jet velocities up to 172 cm/s, and, 3) detect low forward and reverse stenosis (0≤L/D≤2). Regions between the jet termination point and re-establishment of laminar flow (Re≥1500, ≥1000, and ≥110 downstream of 40, 60, and 80 percent stenosis, respectively) cannot presently be detected by this technique.

Effects of Dilution and Nozzle Diameter on Laminar Dimethyl Ether Lifted Flames

2013 ◽  
Author(s):  
Jie Zhou ◽  
Yuhua Ai ◽  
Wenjun Kong
Keyword(s):  
Mass Flow Rate ◽  
Dimethyl Ether ◽  
Mole Fraction ◽  
Flow Rate ◽  
Nozzle Exit ◽  
Nozzle Diameter ◽  
Nitrogen Dilution ◽  
Lifted Flames ◽  
Inner Diameter ◽  
Jet Velocity

This work aimed at studying the effects of nitrogen dilution and nozzle exit inner diameter on the liftoff properties of the dimethyl ether (DME) jet diffusion flames. The liftoff properties including the liftoff position (HL), the critical liftoff velocity (Ulo) and the critical blowout velocity (Ubo) were studied experimentally. In nitrogen dilution experiments, a slowly converging nozzle was used with inner exit diameter of 0.43 mm. When mole fraction of N2 (Z) increased, a) HL increased because the dilution reduced the chemical activity of fuel, in order to achieve stoichiometric conditions, the stabilization point of the lifted flame moved downstream. b) at the critical liftoff condition, the flow rate of DME decreased with the increase of N2, while the total flow rate was almost unchanged, so the jet velocity was almost the same. c) as Z increased, the stabilization zone of the DME liftoff flames became narrow and small. In the experimental study of the effects of the nozzle diameter on the flame liftoff characteristics, six nozzles with i.d. of 0.17mm, 0.25mm, 0.386mm, 0.43mm, 0.693mm and 1.152mm were used. These nozzles had different materials and nozzle exit types. The experimental results showed that the nozzle inner diameter has a significant impact on the flame liftoff characteristics. As the nozzle diameter increased, four types of different liftoff features were observed. The flame was blown out directly with i.d. of 0.17 mm. The DME flame could only be observed liftoff by ignition at a proper position downstream with i.d. of 0.25 mm, 0.386 mm and 0.43 mm. The observations are agreed with that reported in the literatures. While it could be lifted off directly by increasing the mass flow rate of fuel/dilution with i.d. of 0.693 mm. This is the new observation in the present work. It is different from the report in the literatures that the DME flame could not be lifted off directly by increasing the jet velocity except for far field ignition at relatively low mass flow rate. When the nozzle i.d. was increased to 1.152 mm, the DME flames could be lifted off by three different methods: increasing the flow rate of fuel/dilution, decreasing the flow rate of the fuel and ignition the flame downstream. Oscillation lifted DME flames were found with i.d. of 1.152 mm when the fuel was highly diluted by nitrogen. The experimental results also showed that the critical liftoff velocity Ulo and the critical blowout velocity Ubo were strongly dependent on the inner diameter, which decreased with the increase of the nozzle diameter. When the jet velocity was kept constant, the flame liftoff height HL increased with the increase of the nitrogen mole fraction Z for all lifted flames.

Effects of Fuel-Side Nitrogen Dilution on Structure and NOx Formation of Turbulent Syngas Non-premixed Jet Flames

2012 ◽  
Vol 26 (6) ◽  
pp. 3304-3315 ◽  
Author(s):  
Jeongwon Lee ◽  
Sangwoon Park ◽  
Yongmo Kim
Keyword(s):  
Jet Flames ◽  
Nox Formation ◽  
Nitrogen Dilution

Nitrogen Diluted Jet Flames in the Presence of Coflowing Air

2011 ◽  
Author(s):  
James D. Kribs ◽  
Tamir S. Hasan ◽  
Kevin M. Lyons
Keyword(s):  
Diffusion Flame ◽  
Axial Position ◽  
Flammability Limit ◽  
Jet Flames ◽  
Flow Rates ◽  
Nitrogen Dilution ◽  
Flame Shape ◽  
Methane Flow

The purpose of this study is to observe methane jet flames under varying levels of nitrogen dilution and coflowing air. The jet flames were examined in order to determine the conditions for which liftoff and blowout occur under conditions that strain the flame. Methane flow rates were varied, corresponding to intermediate lifted positions to blowout. A sequence of images were taken at each level of dilution and coflow, and were used to determine the lowest radial and axial position of the flammability limit. These flammability regions were compared to the lean flammability limit. It was observed that flame shape and liftoff were considerably more influenced by the effects of the coflowing air compared to the presence of the diluents, and that flames under coflow lost the trailing diffusion flame earlier, which has been shown to be a marker for flame blowout.

Effect of Centrifugal Force on the Performance of High-G Ultra Compact Combustor

2015 ◽  
Author(s):  
Alejandro M. Briones ◽  
Dave L. Burrus ◽  
Timothy J. Erdmann ◽  
Dale T. Shouse
Keyword(s):  
Temperature Profile ◽  
Turbulent Flame ◽  
Flame Length ◽  
Swirl Flow ◽  
Flame Speed ◽  
Reacting Flow ◽  
Flow Conditions ◽  
Radial Temperature ◽  
Turbulent Flame Speed ◽  
Progress Variable

A numerical investigation of reacting flows in an advanced high-g cavity (HGC), Ultra-Compact Combustor (UCC) concept is conducted. The high-g cavity UCC (UCC-HGC) design uses high swirl in a circumferential cavity (CC) wrapped around a main stream annular flow. The high swirl is generated through angled CC driver jets. This centrifugal force is varied by changing the CC-to-core air mass flow ratio (ṁcc/ṁcore) and jet inclination angle (αjet) relative to the cavity ring surface, while maintaining the global equivalence ratio (ϕGlobal) constant. Steady, rotational periodic, 3D simulations are performed following a multiphase, Reynolds-averaged Navier-Stokes (RANS), and non-premixed flamelet/progress variable (FPV) approach using a customized FLUENT. Results indicate that under non-reacting flow conditions the driver jets impose a very strong bulk swirl flow within the CC and the mainstream flow does not entrain into the CC. Thus, the maximum g-load is primarily sensitive to ṁcc/ṁcore and secondarily to αjet. However, the g-loads become increasingly more sensitive to the latter at greater ṁcc/ṁcore. Now, under reacting flow conditions, the flame interacts with the flow and the bulk swirl flow is diminished at low ṁcc/ṁcore, while boosted at high ṁcc/ṁcore. The former happens because the flame deflects the incoming driver jet flow, enhancing radial and axial velocity components (through thermal expansion), while diminishing the tangential flow velocity. This, in turn, weakens the g-loads within the CC to below its design g-load operation. On the other hand, at high ṁcc/ṁcore and small αjet the flame is perpendicular to the bulk swirl flow, accelerating the flow tangential velocity and enhancing g-loads above its design operation. Qualitatively, the more and hotter the flame that can be sustained within the CC the shorter the flame length. The converse is also true. Flame length does not appear to be strongly influenced by ṁcc/ṁcore and αjet. Even though g-loads appear to enhance reaction progress variable source (SC) and, consequently, turbulent flame speed, through turbulence this does not necessarily mean that the turbulent flame speed under g-loads is various factors greater than its corresponding turbulent flame speed under 0g’s. As the ṁcc/ṁcore increases the center-peaked radial temperature profile at intermediate αjet starts to deteriorate, whereas the radial temperature profile at low αjet improves. For high αjet, increasing ṁcc/ṁcore has no substantial effect on the exit radial temperature profiles.

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