Current Issue : January - March Volume : 2013 Issue Number : 1 Articles : 5 Articles
Reduced and normal gravity combustion experiments were performed with fiber-supported methanol droplets with initial\r\ndiameters in the 1mm size range. Experiments were performed with air-diluent mixtures at about 0.101MPa and 298 K, where\r\ncarbon dioxide, helium, or xenon was separately used as the diluent gas. Results indicate that ambient gas transport properties\r\nplay an important role in determining flammability and combustion behaviors including burning rates and radiant heat output\r\nhistories of the droplets. Droplets would burn with significantly higher mole fractions of xenon than helium or carbon dioxide.\r\nIn reduced gravity, droplets would burn steadily with a xenon mole fraction of 0.50 but would not burn steadily if helium or\r\ncarbon dioxide mole fractions were 0.50. Comparison with previous experimental data shows that ignitability and combustion\r\ncharacteristics of droplets are influenced by the fuel type and also the gravitational level. Burning rates were about 40% to 70%\r\nhigher in normal gravity than in reduced gravity. Methanol droplets also had burning rates that were typically larger than 1-\r\npropanol burning rates by about 20% in reduced gravity. In normal gravity, however, burning rate differences between the two\r\nfuels were significantly smaller....
In Korea, municipal solid waste (MSW) treatment is conducted by converting wastes into energy resources using the mechanicalbiological\r\ntreatment (MBT). The small size MSW to be separated from raw MSW by mechanical treatment (MT) is generally\r\ntreated by biological treatment that consists of high composition of food residue and paper and so forth. In this research, the\r\nhydrothermal treatment was applied to treat the surrogate MT residue composed of paper and/or kimchi. It was shown that the\r\nhydrothermal treatment increased the calorific value of the surrogate MT residue due to increasing fixed carbon content and\r\ndecreasing oxygen content and enhanced the dehydration and drying performances of kimchi. Comparing the results of paper\r\nand kimchi samples, the calorific value of the treated product from paper was increased more effectively due to its high content of\r\ncellulose. Furthermore, the change of the calorific value before and after the hydrothermal treatment of the mixture of paper and\r\nkimchi can be well predicted by this change of paper and kimchi only. The hydrothermal treatment can be expected to effectively\r\nconvert high moisture MT residue into a uniform solid fuel....
The potential of a progress variable formulation for predicting autoignition and subsequent kernel development in a nonpremixed\r\njet flame is explored in the LES (Large Eddy Simulation) context. The chemistry is tabulated as a function of mixture fraction and\r\na composite progress variable, which is defined as a combination of an intermediate and a product species. Transport equations\r\nare solved for mixture fraction and progress variable. The filtered mean source term for the progress variable is closed using a\r\nprobability density function of presumed shape for the mixture fraction. Subgrid fluctuations of the progress variable conditioned\r\non the mixture fraction are neglected. A diluted hydrogen jet issuing into a turbulent coflow of preheated air is chosen as a test case.\r\nThe model predicts ignition lengths and subsequent kernel growth in good agreement with experiment without any adjustment\r\nof model parameters. The autoignition length predicted by the model depends noticeably on the chemical mechanism which the\r\ntabulated chemistry is based on. Compared to models using detailed chemistry, significant reduction in computational costs can\r\nbe realized with the progress variable formulation....
Combustion and gasification properties of pulverized coal and char have been investigated experimentally under the conditions of\r\nhigh temperature gradient of order 200?C�·s-1 by a CO2 gas laser beam and CO2-rich atmospheres with 5% and 10% O2. The laser\r\nheating makes a more ideal experimental condition compared with previous studies with a TG-DTA, because it is able to minimize\r\neffects of coal oxidation and combustion by rapid heating process like radiative heat transfer condition. The experimental results\r\nindicated that coal weight reduction ratio to gases followed the Arrhenius equation with increasing coal temperature; further which\r\nwere increased around 5% with adding H2O in CO2-rich atmosphere. In addition, coal-water mixtures with different water/coal\r\nmass ratio were used in order to investigate roles of water vapor in the process of coal gasification and combustion. Furthermore,\r\nchar-water mixtures with different water/char mass ratio were also measured in order to discuss the generation ratio of CO/CO2,\r\nand specified that the source of Hydrocarbons is volatile matter from coal.Moreover, it was confirmed that generations of CO and\r\nHydrocarbons gases are mainly dependent on coal temperature and O2 concentration, and they are stimulated at temperature over\r\n1000?C in the CO2-rich atmosphere....
The impact of particle size distribution (PSD) of pulverized, low rank high volatile content Alaska coal on combustion related\r\npower plant performance was studied in a series of field scale tests. Performance was gauged through efficiency (ratio of megawatt\r\ngenerated to energy consumed as coal), emissions (SO2, NOx, CO), and carbon content of ash (fly ash and bottom ash). The study\r\nrevealed that the tested coal could be burned at a grind as coarse as 50% passing 76 microns, with no deleterious impact on power\r\ngeneration and emissions. The PSD�s tested in this study were in the range of 41 to 81 percent passing 76 microns. There was\r\nnegligible correlation between PSD and the followings factors: efficiency, SO2, NOx, and CO. Additionally, two tests where stack\r\nmercury (Hg) data was collected, did not demonstrate any real difference in Hg emissions with PSD. The results from the field tests\r\npositively impacts pulverized coal power plants that burn low rank high volatile content coals (such as Powder River Basin coal).\r\nThese plants can potentially reduce in-plant load by grinding the coal less (without impacting plant performance on emissions\r\nand efficiency) and thereby, increasing their marketability....
Loading....