Browsing by Subject "high temperature"
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Item Enhancements of a Combustion Vessel to Determine Laminar Flame Speeds of Hydrocarbon Blends with Helium Dilution at Elevated Temperatures and Pressures(2013-04-03) Plichta, DrewFuel 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.Item High temperature oxidation and NaCl-induced accelerated corrosion of hot-dip aluminized 9Cr-1Mo and 310 stainless steel(Texas A&M University, 2005-02-17) Tsaur, Charng-ChengThe behaviors of high temperature corrosion on hot-dip aluminized on 9Cr-1Mo and 310 stainless steels when catalyzed by NaCl and cyclic heating environment were studied experimentally. The corrosion behavior and morphological development were investigated by weight gain kinetics, metallographs, depths of attack, metal losses, and X-ray analyses. The results of 310SS deposited with salt mixtures show that weight gain kinetics in simple oxidation reveals a steady-state parabolic rate law after 3 hr, while the kinetics with salt deposits display multi-stage growth rates. NaCl is the main corrosive specie in high-temperature corrosion involving mixtures of NaCl/Na2SO4 and is responsible for the formation of internal attack. Uniform internal attack is the typical morphology of NaCl-induced hot corrosion, while the extent of intergranular attack is more pronounced as the content of Na2SO4 in the mixture is increased. The thermal-cycling test results of 310SS deposited NaCl and coated 7wt%Si/93wt%Al show that the aluminized layers have good corrosion resistance during the first four cycles of testing, while degradation occurs after testing for five cycles. The reason for degradation of aluminized layers is attributed to the formation of interconnecting voids caused by aluminum inward diffusion, chloridation/oxidation cyclic reactions and the penetration of molten NaCl through the voids into the alloy substrate. The 9Cr-1Mo steels coated with 7wt%Si/93wt%Al oxidized at 750, 850, and 950?C in static air show that oxidation kinetics followed a parabolic rate law at 750 and 850 ?C. The cracks propagated through the FexAly layer due to the growth of brittle FeAl2 and Fe2Al5 at 750 and 850?C. The voids condensed in the interface of intermetallics and substrate are attributed to the Kirkendall effect. At 950?C, the fast growing aluminide layer has a different expansion coefficient than oxide scale, leading to scale cracking, oxygen penetration, and internal oxidized, evidenced by a rapid mass gain.