Browsing by Subject "Laminar flame speed"
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Item Laminar burning velocities and laminar flame speeds of multi-component fuel blends at elevated temperatures and pressures(2011-05) Byun, Jung Joo; Hall, Matthew John; Matthews, Ronald D.; Ellzey, Janet L.; Ezekoye, Ofodike A.; Roberts, Charles E.Iso-octane, n-heptane, ethanol and their blends were tested in a constant volume combustion chamber to measure laminar burning velocities. The experimental apparatus was modified from the previous version to an automatically-controlled system. Accuracy and speed of data acquisition were improved by this modification. The laminar burning velocity analysis code was also improved for minimized error and fast calculation. A large database of laminar burning velocities at elevated temperatures and pressures was established using this improved experimental apparatus and analysis code. From this large database of laminar burning velocities, laminar flame speeds were extracted. Laminar flame speeds of iso-octane, n-heptane and blends were investigated and analysed to derive new correlations to predict laminar flame speeds of any blending ratio. Ethanol and ethanol blends with iso-octane and/or n-heptane were also examined to see the role of ethanol in the blends. Generally, the results for iso-octane and n-heptane agree with published data. Additionally, blends of iso-octane and n-heptane exhibited flame speeds that followed linear blending relationships. A new flame speed model was successfully applied to these fuels. Ethanol and ethanol blends with iso-octane and/or n-heptane exhibited a strongly non-linear blending relationship and the new flame speed model was not applied to these fuels. It was shown that the addition of ethanol into iso-octane and/or n-heptane accelerated the flame speeds.Item Laminar Flame Speeds of Nano-Aluminum/Methane Hybrid Mixtures(2014-12-12) Sikes, TravisAn existing flame speed bomb, which uses optical techniques to measure laminar flame speed, was employed to study the fundamental phenomena of flame propagation through a uniformly dispersed aerosol. In a previous thesis by Andrew Vissotski, the groundwork was laid to begin studies of hybrid flames. Beginning from these preliminary findings, the facility was upgraded to disperse dust into the test chamber through a strong burst of gas. This aerosol was then allowed to settle for a minimum of 45 seconds to ensure that the conditions inside the test chamber were quiescent and that the dust was uniformly distributed. Extinction of laser light through the resulting aerosol was measured through the large optical access with a 632.8-nm, 5-mW HeNe laser so that the mass of suspended nano-particles could be determined as a function of time up until combustion has occurred. The particles used in these experiments were aluminum nano-particles with a manufacturer-stated average fundamental particle size of 100 nm. To properly quantify the particle distribution inside of the vessel, a scanning mobility particle sizer was employed to characterize the aluminum, resulting in an average particle size of 446.1 nm. With a calibrated extinction measurement, experimental suspended mass of aluminum was measured up to 90 mg. A hybrid mixture of Al/CH4 was chosen to serve as the combustion medium and to provide a well-characterized parent fuel to measure the contribution of nano-aluminum on combustion. Two series of experiments were performed, both at stoichiometric conditions: one with the mixture in air and the second with the mixture in a 70/30 N2/O2 mix. The results herein show a maximum decrease in flame speed, 5-7% from the neat mixture, when nano-aluminum is introduced. In the 70/30 N2/O2 mixture, the addition of aluminum results in a maximum decrease of 5 cm/s from the neat flame speed of 80.5 cm/s and in the air mixture, a 2 cm/s maximum decrease from 35.3 cm/s. A preliminary spectroscopic analysis was performed but was inconclusive. It was also found that the addition of nanoparticles cause the flame to become unstable faster when compared to the neat mixture of CH4/air.Item Oxidation Kinetics of Pure and Blended Methyl Octanoate/n-Nonane/Methylcyclohexane: Measurements and Modeling of OH*/CH* Chemiluminescence, Ignition Delay Times and Laminar Flame Speeds(2012-07-16) Rotavera, Brandon MichaelThe focus of the present work is on the empirical characterization and modeling of ignition trends of ternary blends of three distinct hydrocarbon classes, namely a methyl ester (C9H18O2), a linear alkane (n-C9H20), and a cycloalkane (MCH). Numerous surrogate biofuel formulations have been proposed in the literature, yet specific blending of these species has not been studied. Moreover, the effects of blending biofuel compounds with conventional hydrocarbons are not widely studied and a further point is the lack of studies paying specific attention to the effects of fuel variation within a given blended biofuel. To this end, a statistical Design of Experiments L9 array, comprised of 4 parameters (%MO, %MCH, pressure, and equivalence ratio) with 3 levels of variation, constructed in order to systematically study the effects of relative fuel concentrations within the ternary blend enabled variations in fuel concentration for methyl octanoate and MCH of 10% - 30% and 20% - 40%, respectively. Variation in pressure of 1 atm, 5 atm, and 10 atm and in equivalence ratio of 0.5, 1.0, and 2.0 were used, respectively. The fuel-volume percentage of n-nonane varied from 30% - 70%. In total, 10 ternary blends were studied. Ignition delay times for the ternary blends and for the three constituents were obtained by monitoring excited-state OH or CH transitions, A2Epsilon+ -> X2Pi or A2Delta -> X2Pi, respectively, behind reflected shock waves using a heated shock tube facility. Dilute conditions of 99% Ar (vol.) were maintained in all shock tube experiments with the exception of a separate series of n-nonane and MCH experiments under stoichiometric conditions which used 4% oxygen (corresponding to ~ 95% Ar dilution). Temperatures behind reflected shock waves were varied over the range 1243 < T (K) < 1672. From over 450 shock tube experiments, empirical ignition delay time correlations were constructed for all three pure fuels and a master correlation equation for the blended fuels. Ignition experiments conducted on the pure fuels at 1.5 atm indicated the following ignition delay time order, from shortest to longest: methyl octanoate < n-nonane < MCH. With increased pressure to 10 atm (nominal) the order remained, in general, consistent. Under fuel-lean conditions, ignition trends between methyl octanoate and n-nonane exhibited overlap at temperatures below 1350 K, below which the trends diverged with methyl octanoate having shorter ignition delay times. Similar behavior was observed under fuel-rich conditions, yet with the overlap occurring above 1450 K. Stoichiometric ignition trends did not display overlapping behavior under either 1.5 atm or 10 atm pressure. Laminar flame speed measurements were performed at 1 atm and an initial temperature of 443 K on the pure fuel constituents. Additional flame speed measurements of MCH were conducted at 403 K to compare with literature values and were shown to agree strongly with experiments conducted in a constant-volume apparatus. The experiments conducted herein, for the first time, measure laminar flame speeds methyl octanoate. A detailed chemical kinetics mechanism was compiled from three independent, well-validated models for the constituent fuels, where the sub-mechanisms for methyl octanoate and MCH were extracted for integration into a base n-nonane model. The compiled mechanism in the present study (4785 reactions and 1082 species) enables modeling of oxidation processes of the ternary fuel blends of interest. Calculations were performed using the compiled model relative to the base models to assess the impact of utilizing different base chemistry sets. In general, results were reproduced well relative to base models for both n-nonane and MCH, however results for methyl octanoate from both the compiled model and the base model are in disagreement with the results measured herein. Ignition delay times of the fuel blends are well-predicted for several conditions, specifically for blends at lean/high-pressure and stoichiometric/high-pressure conditions, however are not accurately modeled at fuel-rich, high-pressure conditions.