Measurements of Stretch Statistics at Flame Leading Points for High Hydrogen Content Fuels

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Andrew Marshall ◽  
Julia Lundrigan ◽  
Prabhakar Venkateswaran ◽  
Jerry Seitzman ◽  
Tim Lieuwen
Keyword(s):  
Flame Front ◽  
Hydrogen Content ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Fuel Composition ◽  
Mean Flow ◽  
Tangential Strain ◽  
High Hydrogen ◽  
High Hydrogen Content ◽  
Turbulent Flame Speed

Fuel composition has a strong influence on the turbulent flame speed, even at very high turbulence intensities. An important implication of this result is that the turbulent flame speed cannot be extrapolated from one fuel to the next using only the laminar flame speed and turbulence intensity as scaling variables. This paper presents curvature and tangential strain rate statistics of premixed turbulent flames for high hydrogen content (HHC) fuels. Global (unconditioned) stretch statistics are presented as well as measurements conditioned on the leading points of the flame front. These measurements are motivated by previous experimental and theoretical work that suggests the turbulent flame speed is controlled by the flame front characteristics at these points. The data were acquired with high-speed particle image velocimetry (PIV) in a low-swirl burner (LSB). We attained measurements for several H2:CO mixtures over a range of mean flow velocities and turbulence intensities. The results show that fuel composition has a systematic, yet weak effect on curvatures and tangential strain rates at the leading points. Instead, stretch statistics at the leading points are more strongly influenced by mean flow velocity and turbulence level. It has been argued that the increased turbulent flame speeds seen with increasing hydrogen content are the result of increasing flame stretch rates, and therefore, SL,max values, at the flame leading points. However, the differences observed with changing fuel compositions are not significant enough to support this hypothesis. Additional analysis is needed to understand the physical mechanisms through which the turbulent flame speed is altered by fuel composition effects.

Measurements of Stretch Statistics at Flame Leading Points for High Hydrogen Content Fuels

2014 ◽  
Author(s):  
Andrew Marshall ◽  
Julia Lundrigan ◽  
Prabhakar Venkateswaran ◽  
Jerry Seitzman ◽  
Tim Lieuwen
Keyword(s):  
Flame Front ◽  
Hydrogen Content ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Fuel Composition ◽  
Mean Flow ◽  
Tangential Strain ◽  
High Hydrogen ◽  
High Hydrogen Content ◽  
Turbulent Flame Speed

Fuel composition has a strong influence on the turbulent flame speed, even at very high turbulence intensities. An important implication of this result is that the turbulent flame speed cannot be extrapolated from one fuel to the next using only the laminar flame speed and turbulence intensity as scaling variables. This paper presents curvature and tangential strain rate statistics of premixed turbulent flames for high hydrogen content fuels. Global (unconditioned) stretch statistics are presented as well as measurements conditioned on the leading points of the flame front. These measurements are motivated by previous experimental and theoretical work that suggests the turbulent flame speed is controlled by the flame front characteristics at these points. The data were acquired with high speed particle image velocimetry (PIV) in a low swirl burner (LSB). We attained measurements for several H2:CO mixtures over a range of mean flow velocities and turbulence intensities. The results show that fuel composition has a systematic, yet weak effect on curvatures and tangential strain rates at the leading points. Instead, stretch statistics at the leading points are more strongly influenced by mean flow velocity and turbulence level. It has been argued that the increased turbulent flame speeds seen with increasing hydrogen content are the result of increasing flame stretch rates, and therefore SL,max values, at the flame leading points. However, the differences observed with changing fuel compositions are not significant enough to support this hypothesis. Additional analysis is needed to understand the physical mechanisms through which the turbulent flame speed is altered by fuel composition effects.

scholarly journals Investigation of Hydrogen Content and Dilution Effect on Syngas/Air Premixed Turbulent Flame Using OH Planar Laser-Induced Fluorescence

Processes ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1894
Author(s):  
Li Yang ◽  
Wubin Weng ◽  
Yanqun Zhu ◽  
Yong He ◽  
Zhihua Wang ◽  
...  
Keyword(s):  
Hydrogen Content ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Laser Induced Fluorescence ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
High Hydrogen ◽  
Turbulent Flame Speed ◽  
Planar Laser Induced Fluorescence ◽  
Planar Laser

Syngas produced by gasification, which contains a high hydrogen content, has significant potential. The variation in the hydrogen content and dilution combustion are effective means to improve the steady combustion of syngas and reduce NOx emissions. OH planar laser-induced fluorescence technology (OH-PLIF) was applied in the present investigation of the turbulence of a premixed flame of syngas with varied compositions of H2/CO. The flame front structure and turbulent flame velocities of syngas with varied compositions and turbulent intensities were analyzed and calculated. Results showed that the trend in the turbulent flame speed with different hydrogen proportions and dilutions was similar to that of the laminar flame speed of the corresponding syngas. A higher hydrogen proportion induced a higher turbulent flame speed, higher OH concentration, and a smaller flame. Dilution had the opposite effect. Increasing the Reynolds number also increased the turbulent flame speed and OH concentration. In addition, the effect of the turbulence on the combustion of syngas was independent of the composition of syngas after the analysis of the ratio between the turbulent flame speed and the corresponding laminar flame speed, for the turbulent flames under low turbulent intensity. These research results provide a theoretical basis for the practical application of syngas with a complex composition in gas turbine power generation.

Turbulent Consumption Speed Scaling of H2/CO Blends

2011 ◽  
Author(s):  
Prabhakar Venkateswaran ◽  
Andrew D. Marshall ◽  
David R. Noble ◽  
Jerry M. Seitzman ◽  
Tim C. Lieuwen
Keyword(s):  
Laminar Flame ◽  
Turbulent Flame ◽  
Practical Interest ◽  
Flame Speed ◽  
Fuel Composition ◽  
Laminar Flame Speed ◽  
Volume Data ◽  
Mean Flow ◽  
Turbulent Flame Speed ◽  
Kinetic Calculations

This paper describes measurements and analysis of global turbulent consumption speeds, ST,GC, of hydrogen/carbon monoxide (H2/CO) mixtures. The turbulent flame properties of such mixtures are of fundamental interest because of their strong stretch sensitivity and of practical interest since they are the primary constituents of syngas fuels. Data are analyzed at mean flow velocities and turbulence intensities of 4 < U0 < 50 m/s and 1 < u′rms/SL,0 < 100, respectively, for H2/CO blends ranging from 30–90% H2 by volume. Data from two sets of experiments are reported. In the first, fuel blends ranging from 30–90% H2 and mixture equivalence ratio, Φ, were adjusted at each fuel composition to have nominally the same un-stretched laminar flame speed, SL,0. In the second set, equivalence ratios were varied at constant H2 levels. The data clearly corroborate results from other studies that show significant sensitivity of ST,GC to fuel composition. For example, at a fixed u′rms, ST,GC of a 90% H2 case (at Φ = 0.48) is a factor of three times larger than the baseline Φ = 0.9, CH4/air mixture that has the same SL,0 value. We also describe physics-based correlations of these data, using leading points concepts and detailed kinetic calculations of their stretch sensitivities. These results are used to develop an inequality for negative Markstein length flames that bounds the turbulent flame speed data and show that the data can be collapsed using the maximum stretched laminar flame speed, SL,max, rather than SL,0.

Flame Front Characteristic and Turbulent Flame Speed of Lean Premixed Syngas Combustion at Gas Turbine Relevant Conditions

2009 ◽  
Author(s):  
S. Daniele ◽  
P. Jansohn ◽  
K. Boulouchos
Keyword(s):  
Flame Front ◽  
Gas Turbine ◽  
Turbulent Flame ◽  
Front Surface ◽  
Flame Speed ◽  
Inlet Temperature ◽  
Oh Radicals ◽  
High Hydrogen ◽  
Turbulent Flame Speed ◽  
Front Detection

This paper focuses on the description of the turbulent flame speed, at gas turbine like conditions, for different syngas mixtures, selected in order to simulate syngas compositions typically derived from gasification of coal, oil, biomass, and used for power generation in integrated gasification combined cycle (IGCC) processes. In this paper the turbulent flame speed is reported as global consumption rate and calculated based on a mass continuity approach applied to the combustor inlet area and the flame front surface, which was detected experimentally. Flame front detection was done by means of planar laser induced fluorescence technique taking OH radicals as seeding dyes. An in-house developed flame front detection software tool has been further improved and utilized in this work in order to better fit ultra-lean H2-rich flames. Experiments were carried out in a High Pressure Test Rig for operating pressures up to 15 bar. Data provided in this paper will focus on a pressure level of 5 bar, adiabatic flame temperatures up to 1900 K, inlet velocities from 40 to 80 m/s, and inlet temperature of 672 and 772 K. As expected, the results highlight the strongly elevated values of turbulent flame speed for high hydrogen containing fuel gas mixtures. Compared with flame speed data for pure CH4 the ratio (STSyn/STCH4) takes up values of 7 to 8. In absolute terms values go up even beyond 10 m/s. With increased H2 content in the mixture the burning velocity raises, due to the faster chemical kinetics characteristic of this compound and due to physical properties of H2 (Le&lt;1) which enhance flame front corrugation (i.e. flame front surface). Inlet velocity and pressure variations showed to have weak effect on the average flame front position whereas this last parameter is strongly affected by the mixture composition, the equivalence ratio and inlet temperature.

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.

Spark Ignition Simulations and the Generation of Ignition Maps by Means of a Turbulent Flame Speed Closure Approach

2010 ◽  
Author(s):  
Jan M. Boyde ◽  
Massimiliano Di Domenico ◽  
Berthold Noll ◽  
Manfred Aigner
Keyword(s):  
Turbulent Flame ◽  
Spark Ignition ◽  
Flame Speed ◽  
Test Case ◽  
Ignition Energy ◽  
Mean Flow ◽  
Flame Kernel ◽  
Turbulent Flame Speed ◽  
Flow Parameters ◽  
Partially Premixed

This paper presents a numerical investigation of ignition phenomena in turbulent partially premixed methane/air flames. In this work, a turbulent flame speed closure model (TFC) is employed with an ignition delay module extension. The model is applied to two partially premixed test cases under standard conditions in the configuration of a shearless flame and a counter flow flame, respectively. For both setups, the flame kernel propagation and consequent establishment or extinction of the flame are examined. A shearless configuration represents the first test case under investigation. The study demonstrates the large influence of the mean flow parameters on achieving a successful ignition of the domain. The second test case under examination is a counterflow geometry. A sensitivity analysis with respect to spark ignition position and ignition energy is performed. The simulations show that flame kernel spreading is largely influenced by the magnitude of turbulence occurring in the flow, leading to an enhanced propagation in areas with a moderate turbulence degree, whereas high turbulence can be detrimental for the flame establishment due to extensive heat losses. Another observation is that a successful ignition of the domain can occur, even in cases in which the ignition energy is not placed in an area with flammable mixture. The comparison with experimental data shows a good agreement, both in terms of successful ignition and flame kernel propagation.

Effect of Centrifugal Force on Conventional and Alternative Fuel Surrogate Turbulent Premixed Flames

2014 ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar ◽  
Timothy Erdmann
Keyword(s):  
Flame Front ◽  
Centrifugal Force ◽  
Flame Propagation ◽  
Propagation Velocity ◽  
Turbulent Flame ◽  
Premixed Flames ◽  
Flame Speed ◽  
Turbulent Premixed Flames ◽  
Flame Propagation Velocity ◽  
Turbulent Flame Speed

The effect of centrifugal force on flame propagation velocity of stoichiometric propane-, kerosene-, and n-octane-air turbulent premixed flames was numerically examined. The quasi-turbulent numerical model was set in an unsteady two-dimensional geometry with finite length in the transverse and streamwise directions but with infinite length in the spanwise direction. There was relatively good comparison between literature-reported measurements and predictions of propane-air flame propagation velocity as a function of centrifugal force. It was found that for all mixtures the flame propagation velocity increases with centrifugal force. It reaches a maximum then falls off rapidly with further increases in centrifugal force. The results of this numerical study suggest there are no distinct differences among the three mixtures in terms of the effect of centrifugal force on the flame propagation velocity. There are, however, quantitative differences. The numerical models are set in a non-inertial, rotating reference frame. This rotation imposes a radially outward (centrifugal) force. The ignited mixture at one end of the tube raises the temperature and its heat release tends to laminarize the flow. The attained density difference combined with the direction of the centrifugal force promotes Rayleigh-Taylor instability. This instability with thermal expansion and turbulent flame speed constitute the flame propagation mechanism towards the other tube end. A wave is also originated but propagates faster than the flame. During propagation the flame interacts with eddies that wrinkle and/or corrugate the flame. The flame front wrinkles interact with streamtubes that enhance Landau-Darrieus (hydrodynamic) instability, giving rise to a corrugated flame. Under strong stretch conditions the stabilizing equidiffusive-curvature mechanism fails and the flame front breaks up, allowing inflow of unburned mixture into the flame. This phenomenon slows down the flame temporarily and then the flame speeds up faster than before. However, if corrugation is large and the inflow of unburned mixture into the flame is excessive, the latter locally quenches and slows down the flame. This occurs when the centrifugal force is large, tending to blowout the flame. The wave in the tube interacts continuously with the flame through baroclinic torques at the flame front that further enhances the above mentioned flame-eddies interactions. Only at low centrifugal forces the wave intermingles several times with the flame before the averaged flame propagation velocity is determined. The centrifugal force does not substantially increase the turbulent flame speed as commented by previous experimental investigations. The results also suggest that an ultra-compact combustor (UCC) with high-g cavity (HGC) will be limited to centrifugal force levels in the 2000–3000g range.

Effects of Hydrogen Addition on the Flame Speeds of Natural Gas Blends Under Uniform Turbulent Conditions

2015 ◽  
Author(s):  
S. Ravi ◽  
A. Morones ◽  
E. L. Petersen ◽  
F. Güthe
Keyword(s):  
Natural Gas ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Mean Flow ◽  
Hydrogen Addition ◽  
Turbulent Flame Speed ◽  
Preferential Diffusion ◽  
Wide Range ◽  
H2 Addition

Natural gas is the primary fuel for stationary, powergeneration gas turbines, and it is necessary to understand its combustion characteristics under engine-relevant (turbulent) conditions. Since its composition varies depending on the fuel source, a natural gas surrogate (NG 18% C2+) and admixtures with H2 have been utilized recently by the authors to aid chemical kinetics modeling using ignition delay times and laminar flame speed experiments. The present study focused on measuring turbulent flame speeds (displacement speeds) of natural gas (NG2) and methane with H2 using a fan-stirred flame bomb. The apparatus is a closed, cylindrical chamber fitted with four radial impellers that generate a central spherical volume of homogeneous and isotropic turbulence with negligible mean flow. Schlieren imaging was used to visually track the growth of the spherically expanding turbulent kernels during the constant-pressure period. The turbulence levels were fixed at an average RMS intensity level of 1.5 m/s and at an integral length scale of 27 mm. Turbulent flame speeds (ST,0.1) of NG2 blends were measured over a wide range of equivalence ratios between 0.7 and 1.3. ST,0.1 for the natural gas surrogate closely matched with those of methane for near-stoichiometric mixtures. However, preferential-diffusion effects (fuel effects) were observed under turbulent conditions for off-stoichiometric cases. The effects of hydrogen addition on the turbulent flame speeds of NG2 (25/75 and 50/50 (by volume) blends of H2/NG2) were also investigated and were compared with the flame speeds reported in a recent paper by the authors (ASME GT2014-26742) on the effects of hydrogen addition to turbulent flame speeds of methane. The effect of the hydrogen addition was to increase the turbulent flame speed (by about a factor of two for 50% H2 addition), although this effect was much more pronounced for the lean and stoichiometric mixtures. Interestingly, the flame speeds (both laminar and turbulent) of the CH4 blends with H2 were slightly larger than those for the NG2 blend at equivalent conditions, or about 10–20% larger at 50% H2 addition. This behavior can be explained kinetically by the increased importance of the inhibiting reaction CH3 + H (+M) ↔ CH4 (+M), where ethane oxidation produces more CH3 radicals than methane at similar conditions.

Investigation of H2/CH4-Air Flame Characteristics of a Micromix Model Burner at Atmosphere Pressure Condition

2018 ◽  
Author(s):  
Xunwei Liu ◽  
Weiwei Shao ◽  
Yong Tian ◽  
Yan Liu ◽  
Bin Yu ◽  
...  
Keyword(s):  
Hydrogen Content ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Nox Emission ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
High Hydrogen ◽  
Atmosphere Pressure ◽  
Turbulent Flame Speed

For high-hydrogen-content fuel, the Micromix Combustion Technology has been developed as a potential low NOx emission solution for gas turbine combustors, especially for advanced gas turbines with high turbine inlet temperature. Compared with conventional lean premixed flames, multiple distributed slim and micro flames could lead to a lower NOx emission performance for shortening residence time of high temperature flue gas and generally a more uniform temperature distribution. This work aims at micromix flame characteristics of a model burner fueled with hydrogen blending with methane under atmosphere pressure conditions. The model burner assembly was designed to have six concentrically millimeter-sized premixed units around a same unit centrally. Numerical and experimental studies were conducted on mixing performance, flame stability, flame structure and CO/NOx emissions of the model burner. OH radical distribution by OH-PLIF and OH chemiluminescence (OH*) imaging were employed to analyze the turbulence-reaction interactions and characters of the reaction zone at the burner exit. Micromix flames fueled with five different hydrogen content H2-CH4 (60/40, 50/50, 40/60, 30/70, 0/100 Vol.%) were investigated, along with the effects of equivalence ratio and heat load. Results indicated that low NOx emissions of less than 10 ppm (@15% O2) below the exhaust temperature of 1920 K were obtained for all the different fuels. Combustion oscillation didn’t occur for all the conditions. It was found that at a constant flame temperature, the higher the hydrogen content of the fuel, the higher the turbulent flame speed and the weaker the flame lift effect. Combustion noise and NOx emissions also increase with increasing hydrogen content. The OH/OH* signal distribution indicated that a pure methane micromix flame showed a lifted and weaken distributed feature.

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