Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 6 Articles
Two solid pyrolysis models are employed in a concurrent-flow flame spread model to compare the flame structure and spreading characteristics. The first is a zeroth-order surface pyrolysis, and the second is a first-order in-depth pyrolysis. Comparisons are made for samples when the spread rate reaches a steady value and the flame reaches a constant length. The computed results show (1) the mass burning rate distributions at the solid surface are qualitatively different near the flame (pyrolysis base region), (2) the first-order pyrolysis model shows that the propagating flame leaves unburnt solid fuel, and (3) the flame length and spread rate dependence on sample thickness are different for the two cases....
Colombian coffee industry produces about 0.6 million tons of husk (CH) per year which could serve as feedstock for thermal gasification to produce gaseous and liquid fuels. The current paper deals with: (i) CH adiabatic gasification modeling using airsteam blends for partial oxidation and (ii) experimental thermogravimetric analysis to determine the CH activation energy (E). The Chemical Equilibrium with Applications Program (CEA), developed by NASA, was used to estimate the effect of equivalence\r\nratio (ER) and steam to fuel ratio (S : F) on equilibrium temperature and gas composition of ~150 species. Also, an atom balance model was developed for comparison purposes. The results showed that increased ER and (S : F) ratios produce mixtures that are rich in H2 and CO2 but poor in CO. The value for the activation energy was estimated to be 221 kJ/kmol....
A method for evaluating burning velocity in premixed turbulent flames stabilized in divergent mean flows is quantitatively validated using numerical approximations of measured axial profiles of the mean combustion progress variable, mean and conditioned axial velocities, and axial turbulent scalar flux, obtained by four research groups from seven different flames each stabilized in an impinging jet. The method is further substantiated by analyzing the combustion progress variable balance equation that is yielded by the extended Zimont model of premixed turbulent combustion. The consistency of the model with the aforementioned experimental data is also demonstrated....
A new decision support tool, the Wildland Fire Decision Support System (WFDSS) has been developed to support risk-informed decision-making for individual fires in the United States. WFDSS accesses national weather data and forecasts, fire behavior prediction, economic assessment, smoke management assessment, and landscape databases to efficiently formulate and apply information to the decision making process. Risk-informed decision-making is becoming increasingly important as a means of improving fire management and offers substantial opportunities to benefit natural and community resource protection, management response effectiveness, firefighter resource use and exposure, and, possibly, suppression costs. This paper reviews the development, structure, and function of WFDSS, and how it contributes to increased flexibility and agility in decision making, leading to improved fire management program effectiveness....
A series of outdoor experiments were conducted in a fire tunnel to measure the emission of infrared radiation from wildland flames, using a FTIR spectrometer combined with a multispectral camera. Flames of different sizes were produced by the combustion of vegetation sets close to wildland fuel beds, using wood shavings and kermes oak shrubs as fuels. The nongray radiation of the gas-soot mixture was clearly observed from the infrared emitted intensities. It was found that the flame resulting from the combustion of the 0.50?m long fuel bed, with a near-zero soot emission, may be considered as optically thin and that the increase in bed length, from 1 to 4?m, led to an increase in flame thickness, and therefore, in flame emission with contributions from both soot and gases. A further analysis of the emission was conducted in order to evaluate effective flame properties (i.e., emissivity, extinction coefficient, and temperature). The observation of emission spectra suggests thermal nonequilibrium between soot particles and gas species that can be attributed to the presence of relatively cold soot and hot gases within the flame....
A quasi-dimensional modelling study is conducted for the first time for a heavy duty, diesel-fuelled, multicylinder engine operating in HCCI mode. This quasidimensional approach involves a zero-dimensional single-zone homogeneous charge compression ignition (HCCI) combustion model along with a one-dimensional treatment of the intake and exhaust systems. A skeletal chemical kinetic scheme for n-heptane was used in the simulations. Exhaust gas recirculation (EGR) and compression ratio (CR) were the two parameters that were altered in order to deal with the challenges of combustion phasing control and operating load range extension. Results from the HCCI mode simulations show good potential when compared to conventional diesel performance with respect to important performance parameters such as peak firing pressure, specific fuel consumption, peak pressure rise, and combustion noise. This study shows that HCCI combustion mode can be employed at part load of 25% varying the EGR rates between 0 and 60%....
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