Laminar flame speed of a novel liquid bio-fuel has been determined experimentally using a closed spherical combustion vessel of 29 L equipped with two pairs of fused silica windows for optical access at atmospheric pressure and elevated temperature conditions. Schlieren technique was used to visualize and record the temporal evolution of the outwardly spherical flame front, and an in-house developed Matlab code was employed to process the flame front images and calculate its area by applying several image processing techniques. The test conditions consisted of varying the fuel-air mixture equivalence ratio at atmospheric standard pressure and different initial temperatures. Validation of the present method was achieved by measuring and comparing the flame speed of methane/air and n-heptane/air mixture with their published counterparts. Experimental results revealed comparable laminar flame speed of the novel liquid biofuel (1, 3- dimethoxyoctane) to heavy liquid hydrocarbons such as n-heptane and isooctane, especially at stoichiometric and fuel rich conditions. Additionally, the flammability limits of this novel fuel showed similarities with those of gaseous hydrocarbons fuels (e.g. methane, ethane) but higher than those of liquid hydrocarbons (e.g. diesel, gasoline). / February 2016

Gasoline is a complex fuel containing hundreds of species, and, therefore, it is quite difficult to model all components present in gasoline. Alternatively, researchers tend to employ simpler surrogates that mimic targeted physical and chemical properties of gasoline. Two properties of gasoline, i.e., autoignition and laminar flame speed, play key role in the overall performance of spark-ignition and modern engines. For fuel-engine optimization, it is very important to have simple models which can accurately predict autoignition and laminar flame speed of gasoline. In this work, universal laminar flame speed correlation is proposed for typical gasolines. This correlation is based on Monte-Carlo simulations of randomly generated mixtures comprising of 21 gasoline-relevant molecules. Laminar flame speed of each molecule is numerically computed over a wide range of thermodynamic conditions using detailed chemical kinetic models, while flame speed of each mixture is estimated using a mixing rule. The proposed universal correlation is validated against experimentally-measured laminar flame speed of various gasoline fuels.

Synthetic gas, syngas, is a popular alternative fuel for the gas turbine industry, but the composition of syngas can contain different types and amounts of contaminants, such as carbon dioxide, methane, moisture, and nitrogen, depending on the industrial process involved in its manufacturing. The presence of steam in syngas blends is of particular interest from a thermo-chemical perspective as there is limited information available in the literature. This study investigates the effect of moisture content (0 ? 15% by volume), temperature (323 ? 423 K), and pressure (1 ? 10 atm) on syngas mixtures by measuring the laminar flame speed in a newly developed constant-volume, heated experimental facility. This heated vessel also broadens the experimental field of study in the authors? laboratory to low vapor pressure fuels and other vaporized liquids. The new facility is capable of performing flame speed experiments at an initial pressure as high as 30 atm and an initial temperature up to 600 K. Several validation experiments were performed to demonstrate the complete functionality of the flame speed facility. Additionally, a design-of-experiments methodology was used to study the mentioned syngas conditions that are relevant to the gas turbine industry. The design-of-experiments methodology provided the capability to identify the most influential factor on the laminar flame speed of the conditions studied. The experimental flame speed data are compared to the most up-to-date C4 mechanism developed through collaboration between Texas A&M and the National University of Ireland Galway. Along with good model agreement shown with all presented data, a rigorous uncertainty analysis of the flame speed has been performed showing an extensive range of values from 4.0 cm/s to 16.7 cm/s. The amount of carbon monoxide dilution in the fuel was shown to be the most influential factor on the laminar flame speed from fuel lean to fuel rich. This is verified by comparing the laminar flame speed of the atmospheric mixtures. Also, the measured Markstein lengths of the atmospheric mixtures are compared and do not demonstrate a strong impact from any one factor but the ratio of hydrogen and carbon monoxide plays a key role. Mixtures with high levels of CO appear to stabilize the flame structure of thermal-diffusive instability. The increase of steam dilution has only a small effect on the laminar flame speed of high-CO mixtures, while more hydrogen-dominated mixtures demonstrate a much larger and negative effect of increasing water content on the laminar flame speed.

Natural gas is the primary fuel used in industrial gas turbines for power generation. Hydrocarbon blends of methane, ethane, and propane make up a large portion of natural gas and it has been shown that dimethyl ether can be used as a supplement or in its pure form for gas turbine combustion. Because of this, a fundamental understanding of the physical characteristics such as the laminar flame speed is necessary, especially at elevated pressures to have the most relevance to the gas turbine industry. This thesis discusses the equations governing premixed laminar flames, historical methods used to measure the laminar flame speed, the experimental device used in this study, the procedure for converting the measured data into the flame speed, the results of the measurements, and a discussion of the results. The results presented in this thesis include the flame speeds for binary blends of methane, ethane, propane, and dimethyl ether performed at elevated pressures, up to 10-atm initial pressure, using a spherically expanding flame in a constant-volume vessel. Also included in this thesis is a comparison between the experimental measurements and four chemical kinetic models. The C4 mechanism, developed in part through collaboration between the National University of Ireland Galway and Texas A&M, was improved using the data presented herein, showing good agreement for all cases. The effect of blending ethane, propane, and dimethyl ether with methane in binary form is emphasized in this study, with the resulting Markstein length, Lewis number (Le), and flame stability characterized and discussed. It was noticed in this study, as well as in other studies, that the critical radius of the flame typically decreased as the Le decreased, and that the critical radius of the flame increased as the Le increased. Also, a rigorous uncertainty analysis has been performed, showing a range of 0.3 cm/s to 3.5 cm/s depending on equivalence ratio and initial pressure.

Biomass is among the primary alternative energy sources that supplements the fossil fuels to meet today’s energy demand. Gasification is an efficient and environmental friendly technology for converting the energy content in the biomass into a combustible gas mixture, which can be used in various applications. The composition of this gas mixture varies greatly depending on the gasification agent, gasifier design and its operation parameters and can be classified as low and medium LHV gasified biomass. The wide range of possible gas composition between each of these classes and even within each class itself can be a challenge in the combustion for heat and/or power production. The difficulty is primarily associated with the range in the combustion properties that may affect the stability and the emission levels. Therefore, this thesis is intended to provide data of combustion properties for improving the operation or design of atmospheric combustion devices operated with such gas mixtures. The first part of this thesis presents a series of experimental work on combustion of low LHV gasified biomass (a simulated gas mixture of CO/H2/CH4/CO2/N2) with variation in the content of H2O and tar compound (simulated by C6H6). The laminar flame speed, lean blowoff limit and emission levels of low LHV gasified biomass based on the premixed combustion concept are reported in paper I and III. The results show that the presence of H2O and C6H6 in gasified biomass can give positive effects on these combustion parameters (laminar flame speed, lean blowoff limit and emission levels), but also that there are limits for these effects. Addition of a low percentage of H2O in the gasified biomass resulted in almost constant laminar flame speed and combustion temperature of the gas mixture, while its NOx emission and blowoff temperature were decreased. The opposite condition was found when H2O content was further increased. The blowoff limit was shifted to richer fuel equivalence ratio as H2O increased. A temperature limit was observed where CO emission could be maintained at low concentration. With C6H6 addition, the laminar flame speed first decreased, achieved a minimum value, and then increased with further addition of C6H6. The combustion temperature and NOx emission were increased, CO emission was reduced, and blowoff occurs at slightly higher equivalence ratio and temperature when C6H6 content is increased. The comparison with natural gas (simulated by CH4) is also made as can be found in paper I and II. Lower laminar flame speed, combustion temperature, slightly higher CO emission, lower NOx emission and leaner blowoff limit were obtained for low LHV gas mixture in comparison to natural gas. In the second part of the thesis, the focus is put on the combustion of a wide range of gasified biomass types, ranging from low to medium LHV gas mixture (paper IV). The correlation between laminar flame speed or lean blowoff limit and the composition of various gas mixtures was investigated (paper IV). It was found that H2 and content of diluents have higher influence on the laminar flame speed of the gas mixture compared to its CO and hydrocarbon contents. For lean blowoff limit, the diluents have the greatest impact followed by H2 and CO. The mathematical correlations derived from the study can be used to for models of these two combustion parameters for a wide range of gasified biomass fuel compositions. / <p>QC 20130411</p>

Self-propagating High-temperature Synthesis (SHS) is the synthesis of solid materials by a reaction wave propagating into the initial reactants, typically two metals, which can alloy exothermically. Typically, experiments are performed with the reactants in powder form, with relatively low density. Recent experiments by Bacciochini et al. revealed much larger flame speeds in densified powders near TMD (theoritical maximum density), obtained by the cold spray process. The present thesis investigates why the flame speed increases dramatically with an increase in density of the powders. The investigation rests on the analytical model formulated by Makino by controlling how the variables are affected by changes in density. Flame speed measurements were performed in mixtures of nickel (Ni) and aluminum (Al) at different initial densities. The density was varied by controlling the cold-pressing of the samples inside metallic channels and tubes. Experiments were also performed in ball-milled powders, in order to permit comparison with the experiments performed by Bacciochini in these mixtures at nearly maximum densities. The measurements revealed that the flame speed increases with the initial density, with a discontinuous transition occurring at approximately 60% theoretical maximum density (TMD). This transition also corresponds to the point where the powders deform plastically during the compaction process, suggesting that the intimate contact between the particles is responsible for the flame speed increase. The flame speed dependence on powder density is attributed to the changes in the heat conductivity of the pressed powders. At high densities, where the powders have plastically deformed, the continuous structure yields conductivities close to the idealized solid matrix. At these high densities, the conductivity was modeled using the Effective Medium Theory (EMT). Analytical predictions of the flame speed, using available thermo-chemical data for the Al-Ni system were found in good agreement with the present experiments at high densities. At low densities, since Al-Ni is a mixture of loose powders, the EMT model is no longer applicable. Thus, the thermal conductivity was experimentally measured and then was fitted using the semi-empirical model suggested by Aivazov. Using this data, Makino's model predicts the correct flame speed dependence observed experimentally. The present thesis has thus established that the dependence of flame speed on density is due mainly to the changes in the structure and thermal conductivity of the powders.

Fuel flexibility in gas turbines is of particular importance because of the main fuel source, natural gas. Blends of methane, ethane, and propane are big constituents in natural gas and consequently are of particular interest. With this level of importance comes the need for baseline data such as laminar flame speed of said fuels. While flame speeds at standard temperature and pressure have been extensively studied in the literature, experimental data at turbine-like conditions are still lacking currently. This thesis discusses the theory behind laminar flames; new data acquisition techniques; temperature and pressure capability improvements; measured flame speeds; and a discussion of the results including stability analysis. The measured flame speeds were those of methane, ethane, and propane fuel blends, as well as pure methane, at an elevated pressure of 5 atm and temperatures of 298 and 473 K, using a constant-volume, cylindrical combustion vessel. The current Aramco mechanism developed in conjunction with National University of Ireland Galway compared favorably with the data, while the literature data showed discrepancies at stoichiometric to rich conditions. An in-depth flame speed uncertainty analysis yielded a wide range of values from 0.5 cm/s to 21.5 cm/s. It is well known that high-pressure experiments develop flame instabilities when air is used as the oxidizer. In this study, the hydrodynamic instabilities were restrained by using a high diluent-to-oxygen ratio. The thermal-diffusive instabilities were inhibited by using helium as the diluent. To characterize this flame stability, the Markstein length and Lewis number were calculated for the presented conditions. The resultant positive Markstein lengths showed a low propensity of flame speed to flame stretch, while the larger-than-unity Lewis numbers showed the relatively higher diffusivity of helium to that of nitrogen.

Thesis (Ph. D.)--University of Texas at Austin, 2009. / Title from PDF title page (University of Texas Digital Repository, viewed on Aug. 6, 2009). Vita. Includes bibliographical references.

La présente étude s’inscrit dans le cadre d’une évaluation des risques liés d’une part au stockage des déchets nucléaires et d’autre part à la production des semi-conducteurs. L’ojectif est d’obtenir des paramètres fondamentaux sur les propriétés explosives des mélanges hydrogène-protoxyde d’azote et silane-protoxyde d’azote. Pour le système hydrogène-protoxyde d’azote, les temps caractéristiques de réaction derrière une onde de choc réfléchie, les vitesses fondamentales de flamme et les largeurs des cellules de détonation ont été mesurées expérimentalement sur une large gamme de composition et de condition. Un mécanisme cinétique détaillé a été développé et validé sur les données de la présente étude et de la littérature. Des mécanismes cinétiques réduits ont été obtenus par une méthode de réduction automatique et inclus dans un code de simulation numérique bi-dimensionnelle d’onde de détonation. Pour le système silane-protoxyde d’azote, l’évolution temporelle des atomes d’oxygène derrière une onde de choc réfléchie et les vitesses fondamentales de flammes ont été étudiées expérimentalement. Une étude préliminaire d’analyse des produits solides de combustion formés en bombe sphérique a également été réalisée. Un mécanisme cinétique réduit de la littérature a été modifié afin de reproduire les profils des atomes d’oxygène. / The present study is part of a risk assessment related, on one hand, to the storage of nuclear wastes, and on the other hand, to the production of semi-conductors. The aim is to obtain fondamental parameters on the explosive properties of hydrogen-nitrous oxide and silane-nitrous oxide mixtures. For the hydrogen-nitrous oxide system, caracteristic times of reaction behind reflected shock waves, laminar flame speeds and detonation cell widths were measured experimentally over a wide range of composition and condition. A detailed kinetic mechanism has been developed and validated against the data of the present study and of literature. Reduced kinetic mechanisms have been obtained using an automatic method of reduction and included in a two-dimensional numerical simulation code of detonation wave. For the silane-nitrous oxide system, the time profiles of oxygen atoms behind reflected shock waves and laminar flame speeds were studied experimentally. A preliminary analytical study of solid combustion products formed in a spherical bomb was also performed. A reduced kinetic mechanism of the literature was modified to reproduce the profiles of oxygen atoms.

Self-propagating High-temperature Synthesis (SHS) is the synthesis of solid materials by a reaction wave propagating into the initial reactants, typically two metals, which can alloy exothermically. Typically, experiments are performed with the reactants in powder form, with relatively low density. Recent experiments by Bacciochini et al. revealed much larger flame speeds in densified powders near TMD (theoritical maximum density), obtained by the cold spray process. The present thesis investigates why the flame speed increases dramatically with an increase in density of the powders. The investigation rests on the analytical model formulated by Makino by controlling how the variables are affected by changes in density. Flame speed measurements were performed in mixtures of nickel (Ni) and aluminum (Al) at different initial densities. The density was varied by controlling the cold-pressing of the samples inside metallic channels and tubes. Experiments were also performed in ball-milled powders, in order to permit comparison with the experiments performed by Bacciochini in these mixtures at nearly maximum densities. The measurements revealed that the flame speed increases with the initial density, with a discontinuous transition occurring at approximately 60% theoretical maximum density (TMD). This transition also corresponds to the point where the powders deform plastically during the compaction process, suggesting that the intimate contact between the particles is responsible for the flame speed increase. The flame speed dependence on powder density is attributed to the changes in the heat conductivity of the pressed powders. At high densities, where the powders have plastically deformed, the continuous structure yields conductivities close to the idealized solid matrix. At these high densities, the conductivity was modeled using the Effective Medium Theory (EMT). Analytical predictions of the flame speed, using available thermo-chemical data for the Al-Ni system were found in good agreement with the present experiments at high densities. At low densities, since Al-Ni is a mixture of loose powders, the EMT model is no longer applicable. Thus, the thermal conductivity was experimentally measured and then was fitted using the semi-empirical model suggested by Aivazov. Using this data, Makino's model predicts the correct flame speed dependence observed experimentally. The present thesis has thus established that the dependence of flame speed on density is due mainly to the changes in the structure and thermal conductivity of the powders.