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Mohammadreza Baigmohammadi - One of the best experts on this subject based on the ideXlab platform.
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experimental study on the effects of mixture flow rate Equivalence Ratio oxygen enhancement and geometrical parameters on propane air premixed flame dynamics in non adiabatic meso scale reactors
Energy, 2017Co-Authors: Mohammadreza Baigmohammadi, Sadegh Tabejamaat, Morteza FaghanilamraskiAbstract:In the present study, the effects of reactive mixture flow rate, adding oxygen to propane-air mixture, geometrical parameters, and Equivalence Ratio on propane-air/oxygen premixed flame dynamics in ...
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experimental study on the effects of mixture flow rate Equivalence Ratio oxygen enhancement and geometrical parameters on propane air premixed flame dynamics in non adiabatic meso scale reactors
Energy, 2017Co-Authors: Mohammadreza Baigmohammadi, Sadegh Tabejamaat, Morteza FaghanilamraskiAbstract:In the present study, the effects of reactive mixture flow rate, adding oxygen to propane-air mixture, geometrical parameters, and Equivalence Ratio on propane-air/oxygen premixed flame dynamics in non-adiabatic meso-scale reactors were experimentally investigated. During the experiments, seven flame regimes of blow-off, blow-out, asymmetric stationary, stationary-repetitive extinction and re-ignition (RERI), forced/self-RERI, RERI-flash-back, and flash-back were observed. The results showed that increasing the reactive mixture flow rate could generally promote variety of the flame regimes and also improve flame stability in the non-adiabatic meso-scale reactors, especially in 40% and 80% oxygen-enhanced cases. Also, the results demonstrated that increasing the reactor inner diameter and Equivalence Ratio generally extended propane-air- oxygen flame stability and its presence range in the non-adiabatic meso-scale reactors. Moreover, it was shown that increasing the reactor length and also increasing the added oxygen to propane-air mixture more than 40% promoted flame instability and consequently restricted propane-air-oxygen flame presence range in the non-adiabatic meso-scale reactors. Also, it was shown that variations in the mixture flow rate, the reactor length and inner diameter, Equivalence Ratio, and oxygen concentRation in propane-air mixture could significantly influence the flame average propagation speed, acoustic, and chemiluminescence in the non-adiabatic meso-scale reactors.
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experimental study of the effects of geometrical parameters reynolds number and Equivalence Ratio on methane oxygen premixed flame dynamics in non adiabatic cylinderical meso scale reactors with the backward facing step
Chemical Engineering Science, 2015Co-Authors: Mohammadreza Baigmohammadi, Sadegh Tabejamaat, Yasaman FarsianiAbstract:Abstract In this study, we experimentally investigated the effects of geometrical parameters (such as the reactor length ( L ) and the inner diameter ( D R )), the step height ( r in − r R ) , the Reynolds number (Re), and the Equivalence Ratio ( φ )) of the inlet mixture on the behavior of the rich fuel methane–oxygen flames in non-adiabatic cylindrical meso-scale reactors with the backward facing step. During the experiments, seven different flame regimes were observed. These flame regimes were the blow-out, marginal, stationary (stable), RERI, stationary (stable)-flashback, RERI-flashback, and flashback, respectively. Also, the results showed that the length and diameter of reactors could strongly affect flame dynamics, especially the borders among the observed flame regimes in the meso-scale reactors. As a result, it was demonstrated that the reactor length and diameter obviously influenced the traveling speed and frequency of RERI flame regime. Also, it was shown that decreasing the step height from 1.4 mm to 0.4 mm suppressed RERI flame regime in the meso-scale reactors. Moreover, in the certain ranges of the Equivalence Ratio, increasing the Reynolds number decreased the flame presence range in the meso-scale reactors. Finally, it was concluded that RERI flame regime is a prevalent opeRational regime for applications in which an almost uniform temperature pattern on the outer surface of lengthy meso-scale reactors is required. However, it was shown that this privilege was not valid as compared to the temperature distribution patterns caused by the stationary flame regimes in the small length reactors.
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an experimental study of the effects of Equivalence Ratio mixture velocity and nitrogen dilution on methane oxygen pre mixed flame dynamics in a meso scale reactor
Energy Conversion and Management, 2014Co-Authors: Soroush Sarrafan Sadeghi, Mohammadreza Baigmohammadi, Sadegh Tabejamaat, Jalal ZarvandiAbstract:Abstract At the present study, the effects of nitrogen dilution, Equivalence Ratio and inlet mixture velocity on methane–oxygen premixed flame dynamics in a meso-scale reactor with inner diameter of 5 mm has been investigated experimentally. The methane–oxygen premixed flame formation zones and also dynamical behavior of the established flames in a meso-scale reactor have been explored. In this research, the presence of five flame regimes of blow-off, blowout, normal asymmetric, repetitive extinction and re-ignition (RERI), and flashback have been observed. Based on the results of this study, it can be inferred that by increasing the inlet mixture velocity, the Equivalence Ratio should be decreased from fuel rich values toward the stoichiometric value for establishing the flame in a meso-scale reactor. In addition, it has been shown that by increasing the inlet mixture velocity more than a critical value, RERI type of flame may occur. Moreover, increasing the dilution percent at a constant flow rate of oxygen restricted the asymmetric stable flame region and simultaneously extended RERI and blowout regions for the various values of entrance mixture velocities versus Equivalence Ratio. On the contrary, decreasing the dilution percent (to lower than a critical value) could lead the flame to flashback. Also, it was shown that only the asymmetric flame could be formed as a stable flame in such a meso-scale reactor. Moreover, increasing the Equivalence Ratio to the fuel rich side moved the flame location toward the reactor outlet.
Yannis Hardalupas - One of the best experts on this subject based on the ideXlab platform.
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droplet characteristics and local Equivalence Ratio of reacting mixture in spray counterflow flames
Experimental Thermal and Fluid Science, 2014Co-Authors: M. Orain, Yannis HardalupasAbstract:Abstract Spray combustion was studied by injecting monodisperse 125 or 200 μm ethanol droplets in a premixed natural gas fuel flame flowing against an opposed heated air jet. Phase Doppler anemometry and chemiluminescence measurements allowed to characterise both droplet parameters and the local reacting mixture. Both types of droplets crossed the flow stagnation plane and entered the opposite jet. However, 125 μm droplets reversed their motion and oscillated around the stagnation plane, leading to increased droplet residence time in hot regions. The fuel vapour released by droplets close to the stagnation plane, mixed with the surrounding air and led to the ignition of a second fuel vapour flame below the natural gas flame. For 125 μm droplets, mean local Equivalence Ratio of the fuel vapour flame was about 0.8, suggesting lean-premixed combustion; whereas 200 μm droplets led to stoichiometric combustion. “Group Combustion” number was estimated from measurements and suggested that 125 μm and 200 μm droplets burned in different “Group Combustion” regimes.
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spatial resolution of a chemiluminescence sensor for local heat release rate and Equivalence Ratio measurements in a model gas turbine combustor
Experiments in Fluids, 2010Co-Authors: Yannis Hardalupas, C. S. Panoutsos, A M K P TaylorAbstract:The spatial resolution of a Chemiluminescence Sensor, based on focused Cassegrain optics, to detect the location of the reaction zone and heat-release rate in a model gas turbine combustor is reported. The sensor measures simultaneously the chemiluminescent intensities from OH* and CH* excited radicals in flames in order to obtain information on the local flame characteristics. The spatial resolution was evaluated by a combined theoretical and experimental study in laminar and turbulent flames and was supported by detailed chemistry calculations, including the chemiluminescent species, of unstrained one-dimensional flames. The experimental study involved simultaneous measurements of chemiluminescence with the sensor and laser-based reaction rate imaging, using the product of OH and CH2O radicals obtained from planar laser-induced fluorescence (PLIF), and OH PLIF for the location of the reaction zone. The study quantified the influence of flame shape and dimensions and the direction of traverse of the focal region of the sensor through the flames on the spatial resolution, thereby identifying the limitations and optimising the applicability of the sensor. The sensor was used to obtain local time-dependent measurements of heat-release and Equivalence Ratio of a reacting mixture, based on the chemiluminescent intensity Ratio of OH*/CH*, in a swirl-stabilised model gas turbine combustor and quantified the degree of air–fuel premixedness, probability of reaction and power spectra of pressure and chemiluminescent intensity fluctuations in two unsteady flames.
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effect of fuel type on Equivalence Ratio measurements using chemiluminescence in premixed flames
Comptes Rendus Mecanique, 2010Co-Authors: M. Orain, Yannis HardalupasAbstract:Abstract Local temporally-resolved measurements of chemiluminescent intensity from OH ∗ , CH ∗ and C ∗ 2 radicals were obtained in premixed counterflow flames operating with propane and prevaporised fuels (isooctane, ethanol and methanol), for different Equivalence Ratios and strain rates. The results quantified independently the effects of fuel type, strain rate and Equivalence Ratio on chemiluminescent emissions from flames. The ability of chemiluminescent intensity from OH ∗ , CH ∗ and C ∗ 2 radicals to indicate heat release rate depends strongly on fuel type. The intensity Ratio OH ∗ /CH ∗ has a monotonic decrease with Equivalence Ratio for all fuels and can be used to measure Equivalence Ratio of the reacting mixture. For propane and isooctane, the OH ∗ /CH ∗ Ratio remains independent of flame strain rate, whereas some dependence is observed for ethanol and methanol.
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numerical evaluation of Equivalence Ratio measurement using oh and ch chemiluminescence in premixed and non premixed methane air flames
Combustion and Flame, 2009Co-Authors: C. S. Panoutsos, Yannis Hardalupas, A M K P TaylorAbstract:This work presents results from detailed chemical kinetics calculations of electronically excited OH (A{sup 2}{sigma}, denoted as OH{sup *}) and CH (A{sup 2}{delta}, denoted as CH{sup *}) chemiluminescent species in laminar premixed and non-premixed counterflow methane-air flames, at atmospheric pressure. Eight different detailed chemistry mechanisms, with added elementary reactions that account for the formation and destruction of the chemiluminescent species OH{sup *} and CH{sup *}, are studied. The effects of flow strain rate and Equivalence Ratio on the chemiluminescent intensities of OH{sup *}, CH{sup *} and their Ratio are studied and the results are compared to chemiluminescent intensity Ratio measurements from premixed laminar counterflow natural gas-air flames. This is done in order to numerically evaluate the measurement of Equivalence Ratio using OH{sup *} and CH{sup *} chemiluminescence, an experimental practise that is used in the literature. The calculations reproduced the experimental observation that there is no effect of strain rate on the chemiluminescent intensity Ratio of OH{sup *} to CH{sup *}, and that the Ratio is a monotonic function of Equivalence Ratio. In contrast, the strain rate was found to have an effect on both the OH{sup *} and CH{sup *} intensities, in agreement with experiment. The calculated OH{sup *}/CH{supmore » *} values showed that only five out of the eight mechanisms studied were within the same order of magnitude with the experimental data. A new mechanism, proposed in this work, gave results that agreed with experiment within 30%. It was found that the location of maximum emitted intensity from the excited species OH{sup *} and CH{sup *} was displaced by less than 65 and 115 {mu}m, respectively, away from the maximum of the heat release rate, in agreement with experiments, which is small relative to the spatial resolution of experimental methods applied to combustion applications, and, therefore, it is expected that intensity from the OH{sup *} and CH{sup *} excited radicals can be used to identify the location of the reaction zone. Calculations of the OH{sup *}/CH{sup *} intensity Ratio for strained non-premixed counterflow methane-air flames showed that the intensity Ratio takes different values from those for premixed flames, and therefore has the potential to be used as a criterion to distinguish between premixed and non-premixed reaction in turbulent flames. (author)« less
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local Equivalence Ratio and degree of premixedness of reacting mixture in swirl stabilised natural gas fuelled burners
43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005Co-Authors: Yannis Hardalupas, M. OrainAbstract:Local, time-dependent measurements of Equivalence Ratio of the reacting mixture and degree of non-stoichiometric (premixed) reaction were obtained in a swirl-stabilised natural gas-fuelled, nonpremixed burner using the intensity of Chemiluminescence from flame radicals. The measurements quantified the mean, rms of fluctuations and probability density functions of local Equivalence Ratio, heat release and probability of premixed, lean or rich, versus stoichiometric reaction at the stabilisation region of the flame. The burner was operated over a range of air flow Reynolds numbers from 18970 till 57600, overall Equivalence Ratio of 0.32 and imposed oscillations on the air flow to the burner at the resonance frequency of 350 Hz. The results show that the local mean Equivalence Ratio at the flame base was stoichiometric, but with large fluctuations to suggest that around 80% of the reaction was premixed either lean or rich. The degree of premixed reaction increased with axial distance from the burner exit and Reynolds number and the lean premixed reaction dominated. Imposed air flow oscillations lifted the flame and led to nearly fully premixed reaction.
Ahmed F Ghoniem - One of the best experts on this subject based on the ideXlab platform.
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investigations into the impact of the Equivalence Ratio on turbulent premixed combustion using particle image velocimetry and large eddy simulation techniques v and m flame configuRations in a swirl combustor
Energy & Fuels, 2016Co-Authors: Gaurav Kewlani, Santosh J Shanbhogue, Ahmed F GhoniemAbstract:Turbulent premixed combustion is studied using experiments and numerical simulations in an acoustically uncoupled cylindrical sudden-expansion swirl combustor, and the impact of the Equivalence Ratio on the flame–flow characteristics is analyzed. In order to numerically capture the inherent unsteadiness exhibited in the flow, the large eddy simulation (LES) technique based on the artificial flame thickening combustion model is employed. The experimental data are obtained using particle image velocimetry. It is observed that changes in heat loading, in the presence of wall confinement, significantly influence the flow field in the wake region, the stabilization location of the flame, and the flame intensity. Specifically, increasing the Equivalence Ratio drastically reduces the average inner recirculation zone size and causes transition of the flame macrostructure from the “V” configuRation to the “M” configuRation. In other words, while the flame stabilizes along the inner shear layer for the V flame, a p...
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investigation of a turbulent premixed combustion flame in a backward facing step combustor effect of Equivalence Ratio
Energy, 2016Co-Authors: Medhat A Nemitallah, Gaurav Kewlani, Seunghyuck Hong, Santosh J Shanbhogue, Mohamed A Habib, Ahmed F GhoniemAbstract:Abstract In the present study, LES (large-eddy simulation) is utilized to analyze lean-premixed propane-air flame stability in a backward-step combustor over a range of Equivalence Ratio. The artificially thickened flame approach coupled with a reduced reaction mechanism is incorporated for modeling the turbulence–combustion interactions at small scales. Simulation results are compared to high-speed PIV (particle image velocimetry) measurements for validation. The results show that the numerical framework captures different topological flow features effectively and with reasonable accuracy, for stable flame configuRations, but some quantitative differences exist. The RZ (recirculation zone) is formed of a primary eddy and a secondary eddy and its overall size is significantly impacted by the Equivalence Ratio. The temperature distribution inside the recirculation zone is highly non-uniform, with much lower values observed close to the backward step and the bottom wall. The mixture distribution inside the RZ is also non-uniform because of mixing with reactants and heat loss to the walls. The flame is stabilized closer to the backward step as the Equivalence Ratio increases. At lower fuel fractions, the flame lifts off the step starting at Equivalence Ratio of 0.63 and the lift off distance is increased while the Equivalence Ratio is lowered.
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investigation of a turbulent premixed combustion flame in a backward facing step combustor effect of Equivalence Ratio
Energy, 2016Co-Authors: Medhat A Nemitallah, Gaurav Kewlani, Seunghyuck Hong, Santosh J Shanbhogue, Mohamed A Habib, Ahmed F GhoniemAbstract:In the present study, LES (large-eddy simulation) is utilized to analyze lean-premixed propane-air flame stability in a backward-step combustor over a range of Equivalence Ratio. The artificially thickened flame approach coupled with a reduced reaction mechanism is incorporated for modeling the turbulence–combustion interactions at small scales. Simulation results are compared to high-speed PIV (particle image velocimetry) measurements for validation. The results show that the numerical framework captures different topological flow features effectively and with reasonable accuracy, for stable flame configuRations, but some quantitative differences exist. The RZ (recirculation zone) is formed of a primary eddy and a secondary eddy and its overall size is significantly impacted by the Equivalence Ratio. The temperature distribution inside the recirculation zone is highly non-uniform, with much lower values observed close to the backward step and the bottom wall. The mixture distribution inside the RZ is also non-uniform because of mixing with reactants and heat loss to the walls. The flame is stabilized closer to the backward step as the Equivalence Ratio increases. At lower fuel fractions, the flame lifts off the step starting at Equivalence Ratio of 0.63 and the lift off distance is increased while the Equivalence Ratio is lowered.
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impact of Equivalence Ratio on the macrostructure of premixed swirling ch4 air and ch4 o2 co2 flames
ASME Turbo Expo 2015: Turbine Technical Conference and Exposition, 2015Co-Authors: Hirotatsu Watanabe, Santosh J Shanbhogue, Ahmed F GhoniemAbstract:Premixed CH4/O2/CO2 flames (oxy-flames) and CH4/air flames (air-flames) were experimentally studied in a swirl-stabilized combustor. For comparing oxy and air flames, the same Equivalence Ratio and adiabatic flame temperature were used. CO2 dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the Equivalence Ratio and Reynolds number (=20,000) the same. For high Equivalence Ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the Equivalence Ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuRation. Calculations at the Equivalence Ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher Equivalence Ratio, and the cross point of the extinction strain rate appears at Equivalence Ratio of 0.64.Copyright © 2015 by ASME
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the impact of Equivalence Ratio oscillations on combustion dynamics in a backward facing step combustor
Combustion and Flame, 2009Co-Authors: Murat H Altay, Raymond L Speth, Duane E Hudgins, Ahmed F GhoniemAbstract:Abstract The combustion dynamics of propane–air flames are investigated in an atmospheric pressure, atmospheric inlet temperature, lean, premixed backward-facing step combustor. We modify the location of the fuel injector to examine the impact of Equivalence Ratio oscillations arriving at the flame on the combustion dynamics. Simultaneous pressure, velocity, heat-release rate and Equivalence Ratio measurements and high-speed video from the experiments are used to identify and characterize several distinct operating modes. When the fuel is injected far upstream from the step, the Equivalence Ratio arriving at the flame is steady and the combustion dynamics are controlled only by flame–vortex interactions. In this case, different dynamic regimes are observed depending on the operating parameters. When the fuel is injected close to the step, the Equivalence Ratio arriving at the flame exhibits oscillations. In the presence of Equivalence Ratio oscillations, the measured sound pressure level is significant across the entire range of lean mean Equivalence Ratios even if the Equivalence Ratio oscillations arriving at the flame are out-of-phase with the pressure oscillations. The combustion dynamics are governed primarily by the flame–vortex interactions, while the Equivalence Ratio oscillations have secondary effects. The Equivalence Ratio oscillations could generate variations in the combustion dynamics in each cycle under some operating conditions, destabilize the flame at the entire range of the lean Equivalence Ratios, and increase the value of the mean Equivalence Ratio at the lean blowout limit.
Milford A. Hanna - One of the best experts on this subject based on the ideXlab platform.
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steam air fluidized bed gasification of distillers grains effects of steam to biomass Ratio Equivalence Ratio and gasification temperature
Bioresource Technology, 2009Co-Authors: Ajay Kumar, David D Jones, Kent M Eskridge, Milford A. HannaAbstract:In this study, thermochemical biomass gasification was performed on a bench-scale fluidized-bed gasifier with steam and air as fluidizing and oxidizing agents. Distillers grains, a non-fermentable byproduct of ethanol production, were used as the biomass feedstock for the gasification. The goal was to investigate the effects of furnace temperature, steam to biomass Ratio and Equivalence Ratio on gas composition, carbon conversion efficiency and energy conversion efficiency of the product gas. The experiments were conducted using a 3 � 3 � 3 full factorial design with temperatures of 650, 750 and 850 C, steam to biomass Ratios of 0, 7.30 and 14.29 and Equivalence Ratios of 0.07, 0.15 and 0.29. Gasification temperature was found to be the most influential factor. Increasing the temperature resulted in increases in hydrogen and methane contents, carbon conversion and energy efficiencies. Increasing Equivalence Ratio decreased the hydrogen content but increased carbon conversion and energy efficiencies. The steam to biomass Ratio was optimal in the intermediate levels for maximal carbon conversion and energy efficiencies.
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steam air fluidized bed gasification of distillers grains effects of steam to biomass Ratio Equivalence Ratio and gasification temperature
Bioresource Technology, 2009Co-Authors: Ajay Kumar, David D Jones, Kent M Eskridge, Milford A. HannaAbstract:In this study, thermochemical biomass gasification was performed on a bench-scale fluidized-bed gasifier with steam and air as fluidizing and oxidizing agents. Distillers grains, a non-fermentable byproduct of ethanol production, were used as the biomass feedstock for the gasification. The goal was to investigate the effects of furnace temperature, steam to biomass Ratio and Equivalence Ratio on gas composition, carbon conversion efficiency and energy conversion efficiency of the product gas. The experiments were conducted using a 3x3x3 full factorial design with temperatures of 650, 750 and 850 degrees C, steam to biomass Ratios of 0, 7.30 and 14.29 and Equivalence Ratios of 0.07, 0.15 and 0.29. Gasification temperature was found to be the most influential factor. Increasing the temperature resulted in increases in hydrogen and methane contents, carbon conversion and energy efficiencies. Increasing Equivalence Ratio decreased the hydrogen content but increased carbon conversion and energy efficiencies. The steam to biomass Ratio was optimal in the intermediate levels for maximal carbon conversion and energy efficiencies.
M. Orain - One of the best experts on this subject based on the ideXlab platform.
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droplet characteristics and local Equivalence Ratio of reacting mixture in spray counterflow flames
Experimental Thermal and Fluid Science, 2014Co-Authors: M. Orain, Yannis HardalupasAbstract:Abstract Spray combustion was studied by injecting monodisperse 125 or 200 μm ethanol droplets in a premixed natural gas fuel flame flowing against an opposed heated air jet. Phase Doppler anemometry and chemiluminescence measurements allowed to characterise both droplet parameters and the local reacting mixture. Both types of droplets crossed the flow stagnation plane and entered the opposite jet. However, 125 μm droplets reversed their motion and oscillated around the stagnation plane, leading to increased droplet residence time in hot regions. The fuel vapour released by droplets close to the stagnation plane, mixed with the surrounding air and led to the ignition of a second fuel vapour flame below the natural gas flame. For 125 μm droplets, mean local Equivalence Ratio of the fuel vapour flame was about 0.8, suggesting lean-premixed combustion; whereas 200 μm droplets led to stoichiometric combustion. “Group Combustion” number was estimated from measurements and suggested that 125 μm and 200 μm droplets burned in different “Group Combustion” regimes.
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effect of fuel type on Equivalence Ratio measurements using chemiluminescence in premixed flames
Comptes Rendus Mecanique, 2010Co-Authors: M. Orain, Yannis HardalupasAbstract:Abstract Local temporally-resolved measurements of chemiluminescent intensity from OH ∗ , CH ∗ and C ∗ 2 radicals were obtained in premixed counterflow flames operating with propane and prevaporised fuels (isooctane, ethanol and methanol), for different Equivalence Ratios and strain rates. The results quantified independently the effects of fuel type, strain rate and Equivalence Ratio on chemiluminescent emissions from flames. The ability of chemiluminescent intensity from OH ∗ , CH ∗ and C ∗ 2 radicals to indicate heat release rate depends strongly on fuel type. The intensity Ratio OH ∗ /CH ∗ has a monotonic decrease with Equivalence Ratio for all fuels and can be used to measure Equivalence Ratio of the reacting mixture. For propane and isooctane, the OH ∗ /CH ∗ Ratio remains independent of flame strain rate, whereas some dependence is observed for ethanol and methanol.
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local Equivalence Ratio and degree of premixedness of reacting mixture in swirl stabilised natural gas fuelled burners
43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005Co-Authors: Yannis Hardalupas, M. OrainAbstract:Local, time-dependent measurements of Equivalence Ratio of the reacting mixture and degree of non-stoichiometric (premixed) reaction were obtained in a swirl-stabilised natural gas-fuelled, nonpremixed burner using the intensity of Chemiluminescence from flame radicals. The measurements quantified the mean, rms of fluctuations and probability density functions of local Equivalence Ratio, heat release and probability of premixed, lean or rich, versus stoichiometric reaction at the stabilisation region of the flame. The burner was operated over a range of air flow Reynolds numbers from 18970 till 57600, overall Equivalence Ratio of 0.32 and imposed oscillations on the air flow to the burner at the resonance frequency of 350 Hz. The results show that the local mean Equivalence Ratio at the flame base was stoichiometric, but with large fluctuations to suggest that around 80% of the reaction was premixed either lean or rich. The degree of premixed reaction increased with axial distance from the burner exit and Reynolds number and the lean premixed reaction dominated. Imposed air flow oscillations lifted the flame and led to nearly fully premixed reaction.
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local measurements of the time dependent heat release rate and Equivalence Ratio using chemiluminescent emission from a flame
Combustion and Flame, 2004Co-Authors: Yannis Hardalupas, M. OrainAbstract:Abstract Chemiluminescent emissions from OH⋅, CH⋅, and C⋅2 and continuous emissions from CO⋅2 have been measured in natural-gas-fuelled, premixed, counterflow flames operating with an Equivalence Ratio between 0.7 and 1.3 and strain rates between 80 and 400 s−1, achieved by varying the exit velocity of the jet between 1 and 5 m s−1. Cassegrain receiving optics coupled to a high-performance spectroscopic unit allowed local, temporally resolved measurements of intensity of chemiluminescence in flat flames, which were compared with measurements along a line of sight obtained from flame spectra. This study allowed independent evaluation of the effects of strain rate and Equivalence Ratio on intensity of chemiluminescence and the ability of intensity of chemiluminescence to indicate heat release rate. Results suggest that intensities of chemiluminescence from OH⋅ and CH⋅ and background intensity from CO⋅2 are good indicators of heat release rate, whereas that from C⋅2 is not. The study also evaluated the ability to measure Equivalence Ratio of the reacting mixture using intensity of chemiluminescence and found that the intensity Ratio OH⋅/CH⋅ has a monotonic decrease with Equivalence Ratio for lean and stoichiometric mixtures, while remaining independent of flame strain rate. The results indicate that the intensity Ratio OH⋅/CH⋅ can measure with uncertainties of 5% the Equivalence Ratio up to values of 1.1 and with uncertainties of 20% for richer mixtures due to the low sensitivity of the intensity Ratio OH⋅/CH⋅ for rich mixtures. The intensity Ratios of C⋅2/OH⋅ and C⋅2/CH⋅ have a non-monotonic dependence on Equivalence Ratio and a dependence on strain rate and are thus not suitable for measurements of Equivalence Ratio. An approach to measuring the time-dependent Equivalence Ratio of the reacting mixture is suggested and data processing methods and associated uncertainties are presented. The potential of the technique for local measurements in practical burners is discussed and further evaluation of the spatial resolution is required in such flames. However, suggestions have been provided on how the spatial resolution can be improved in practical flames.
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Chemiluminescence sensor for local Equivalence Ratio of reacting mixtures of fuel and air (FLAMESEEK)
Applied Thermal Engineering, 2004Co-Authors: Yannis Hardalupas, M. Orain, C. S. Panoutsos, Alexander Taylor, Jimmy Olofsson, Hans Seyfried, Mattias Richter, Johan Hult, Marcus Aldén, Fredrik HermannAbstract:This paper describes a Cassegrain optics-based chemiluminescence sensor (CS) for measurements in gas turbine combustors. The chemiluminescence sensor measures the Equivalence Ratio of reacting fuel and air mixtures, and can identify the flame location, in partially premixed flames. It has the potential for monitoring the degree of premixedness of reacting fuel and air in industrial gas turbine combustors, where opeRation with lean premixed mixtures is important for reduction of NO, emissions. The spatial resolution of the sensor is evaluated by comparing OH* chemiluminescence measurement from the CS with laser induced OH fluorescence, in the cone-shaped premixed flame of a Bunsen burner. The ability of the sensor to measure in a modified micro-gas turbine environment burning a methane/air, as well as, a methane/ water/air flame (humidified flame) is also demonstrated. (Less)