A espectroscopia de emissão foi utilizada na determinação da temperatura de chamas pré-misturadas de GLP. Investigou-se a emissão natural de radicais CH * em três diferentes condições de queima: razão estequiométrica de combustível/oxidante, excesso de combustível (chama rica) e excesso de oxidante (chama pobre). O valor médio obtido para a temperatura rotacional de CH * foi de 2845 70 K nas condições utilizadas nos experimentos. Esse valor não variou significativamente com os demais tipos de chama e é compatível com os cálculos de temperatura adiabática dos sistemas estudados. Essa temperatura também é concordante com resultados obtidos por via indireta, utilizando-se o método de linha reversa de sódio, que consiste em uma técnica bem estabelecida e independente da emissão natural. Temperaturas vibracionais de ca. 4600 K foram calculadas, indicando que o tempo de vida do CH * não é suficiente para que o equilíbrio entre os modos rotacionais e vibracionais seja estabelecido.Emission spectroscopy was used in the temperature determination of LPG (liquefied petroleum gas) premixed flames. Natural emission of CH * radicals was investigated in flames under three different burning conditions: fuel/oxydizer stoichiometric ratio, fuel excess (rich flame), and oxidizer excess (lean flame). An average value of 2845 70 K was obtained for CH * rotational temperature in the set up used in the experiments. This value did not show significant change with the type of flame analyzed and it is compatible with the calculated adiabatic flame temperatures of the investigated systems. This temperature value also agrees with that determined by an indirect measurement, using the sodium line reversal method, which is independent from the radical natural emission and well established in literature. Vibrational temperatures of ca. 4600 K were calculated, indicating that the CH * lifetime is insufficient for the establishment of an equilibrium state between the rotational and vibrational modes.
Rotational temperatures of CH * species present in ethanol flames with different diluent gas compositions were determined using natural emission spectroscopy. Spectrum fine-structures showed two different rotational temperatures. The results of A′′ symmetry levels were slightly higher than A′ for all flames investigated. The temperature values also indicated a non-equilibrium distribution.
A single-image nitric-oxide molecular tagging velocimetry (NO-MTV) is reported and employed in a real air driven hypersonic shock tunnel and provided velocities of 3240 ± 170(5.2%) and 3030 ± 160(5.3%) m s − 1 , insignificantly different from previous results of 3037 ± 98(3.2%) obtained by an ordinary multi-image MTV technique. The proposed methodology relies on an one-dimensional analytical description of the spatial intensity profile registered by a single MTV image.
The C 2 * radical is used as a system probe tool to the reactive flow diagnostic, and it was chosen due to its large occurrence in plasma and combustion in aeronautics and aerospace applications. The rotational temperatures of C 2 * species were determined by the comparison between experimental and theoretical data. The simulation code was developed by the authors, using C++ language and the object oriented paradigm, and it includes a set of new tools that increase the efficacy of the C 2 * probe to determine the rotational temperature of the system. A brute force approach for the determination of spectral parameters was adopted in this version of the computer code. The statistical parameter c 2 was used as an objective criterion to determine the better match of experimental and synthesized spectra. The results showed that the program works even with low-quality experimental data, typically collected from in situ airborne compact apparatus. The technique was applied to flames of a Bunsen burner, and the rotational temperature of ca. 2100 K was calculated.
In this work the presence of soot in laminar diffusion of diesel and blends diesel/biodiesel flames were investigated in the following proportions: 5, 10, 20 and 50% of biodiesel. The technique of laser-induced incandescence (LII) was used for the soot detection. Horizontal mapping were performed at two heights (80 and 260 mm above the burner) to investigate the distribution of soot along the studied flames. The experiment was performed with a pulsed Nd:YAG laser with the wavelength of 1064 nm. The results have shown that the soot emission decreases as the amount of biodiesel increases in the blends. Keywords: laser-induced incandescence, soot, biodiesel, combustion IntroductionDiesel engines are currently the largest source of power generation in the planet. They are widely used in quite different areas, as transportation and mining machinery. They are popular due to their high efficiency, low-cost and durability if compared with gasoline and other automotive fuels.1,2 Nevertheless, diesel engines also presents another remarkable feature: they are largely responsible by the emission of soot, one of most pollutants of environment. 3 Soot is basically formed by particles of impure carbon, with diameter from 10 to 50 nm. Due to its small size, soot particles can penetrate in the lung alveolus of human beings causing serious respiratory and cardiac diseases. 4 Besides health and ecological issues, soot also plays an inconvenient role in the energy generation from combustion processes. [5][6][7] In general, the presence of soot diminishes the overall efficiency of the combustion processes. Soot production is associated to the cracking reactions of hydrocarbon chains that generate carbon solid clusters. These reactions are carried out in gaseous phase and compete directly with the mechanism of oxidation of hydrocarbons that are responsible to the energy release. 8It means that soot is preferentially formed in fuel-rich and high temperature combustion flames, as diffusive flames. These flames are largely used as industrial energy sources. In diffusive flames, as the fuel is burned using only the oxygen available from surroundings, soot presence is higher than the other kind of flames, like premixed ones In some specific applications, like boiler devices, however, a moderate amount of soot is desirable, as its presence increases the heat transfer rate.7 Soot is also quite important in the production of carbon black, which is employed as active filler in rubber products and as component of printing paints.Among the strategies to reduce soot emission from diesel engines, recently a vegetable fuel, known as biodiesel, has been developed. 9 Biodiesel is a kind of biofuel made by alkyl esters from long-chain fatty acids derived from vegetable oils or animal fat. Biodiesel shows a better flammability if compared to other biofuels, and can replace the diesel oil, or diesel/biodiesel blends, in compression ignition engines without significant changes. 10It also presents the following advantages over pure diesel: there are no a...
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