Thermal radiation in combustion systems

A numerical procedure for solving the nongray radiative transfer equation (RTE) in two-dimensional cylindrical participating media is presented. Nongray effects are treated by using a narrow-band approach. Radiative emission from CO, CO2, H2O, CH4 and soot is considered. The solution procedure is applied to study radiative heat transfer in a premixed CH4-O2, laminar, flame. Temperature, soot and IR-active species molar fraction distributions are allowed to vary in the axial direction of the flame. From the obtained results it is possible to quantify the radiative loss in the flame, as well as the importance of soot radiation as compared to gaseous radiation. Since the solution procedure is developed for a two-dimensional cylindrical geometry, it can be applied to other combustion systems such as furnaces, internal combustion engines, liquid and solid propellant combustion.

CHRONIC CHAGASIC CARDIOPATHY: THE PRODUCT OF A TURBULENT HOST-PARASITE RELATIONSHIP

The pathogenesis of chronic chagasic cardiopathy is still a debated matter. In this review, the main theories raised about it since the first description of the disease in 1909 by Carlos Chagas, are considered. The scarcity of T.cruzi parasites into the myocardium and the apparent lack of correlation between their presence and the occurrence of myocardial inflammatory infiltrate, have originated many theories indicating that chronic Chagas' cardiopathy is an autoimmune disease. Recently however, papers using immunohistochemical technique or PCR have demonstrated a strong association between moderate or severe myocarditis and presence of T.cruzi Ags, indicating a direct participation of the parasite in the genesis of chronic chagasic myocarditis. Different patterns of cytokine production seem to have important role in the outcome of the disease. Participation of the microcirculatory alterations and fibrosis as well as the relationship with the parasite are also emphasized. Finally, the author suggests that the indeterminate form of the disease occurs when the host immunological response against the parasite is more efficient while the chronic cardiopathy occurs in patients with hyperergic and inefficient immune response

Elephant grass genotypes for bioenergy production by direct biomass combustion

The objective of this work was to evaluate elephant grass (Pennisetum purpureum Schum.) genotypes for bioenergy production by direct biomass combustion. Five elephant grass genotypes grown in two different soil types, both of low fertility, were evaluated. The experiment was carried out at Embrapa Agrobiologia field station in Seropédica, RJ, Brazil. The design was in randomized complete blocks, with split plots and four replicates. The genotypes studied were Cameroon, Bag 02, Gramafante, Roxo and CNPGL F06-3. Evaluations were made for biomass production, total biomass nitrogen, biomass nitrogen from biological fixation, carbon/nitrogen and stem/leaf ratios, and contents of fiber, lignin, cellulose and ash. The dry matter yields ranged from 45 to 67 Mg ha-1. Genotype Roxo had the lowest yield and genotypes Bag 02 and Cameroon had the highest ones. The biomass nitrogen accumulation varied from 240 to 343 kg ha-1. The plant nitrogen from biological fixation was 51% in average. The carbon/nitrogen and stem/leaf ratios and the contents of fiber, lignin, cellulose and ash did not vary among the genotypes. The five genotypes are suitable for energy production through combustion.

A thermogravimetric analysis of the combustion of a Brazilian mineral coal

Knowledge of coal combustion kinetics is crucial for burner design. This work aims to contribute on this issue by determining the kinetics of a particular Brazilian bituminous coal. Non-isothermal thermogravimetry was applied for determining both the pre-exponential factor and the activation energy. Coal samples of 10 mg and 775 mm mean size were used in synthetic air atmospheres (21 % O2). Heating rates from 10 to 50 ºC/min were applied until the temperature reached 850 ºC, which was kept constant until burnout. The activation energy for the primary and the secondary combustion resulted, respectively, in 135.1 kJ/mol and 85.1 kJ/mol.

Diesel/biodiesel soot oxidation with ceo2 and ceo2-zro2-modified cordierites: a facile way of accounting for their catalytic ability in fuel combustion processes

CeO2 and mixed CeO2-ZrO2 nanopowders were synthesized and efficiently deposited onto cordierite substrates, with the evaluation of their morphologic and structural properties through XRD, SEM, and FTIR. The modified substrates were employed as outer heterogeneous catalysts for reducing the soot originated from the diesel and diesel/biodiesel blends incomplete combustion. Their activity was evaluated in a diesel stationary motor, and a comparative analysis of the soot emission was carried out through diffuse reflectance spectroscopy. The analyses have shown that the catalyst-impregnated cordierite samples are very efficient for soot oxidation, being capable of reducing the soot emission in more than 60%.

Palladium-supported catalysts in methane combustion: comparison of alumina and zirconia supports

Palladium catalysts supported on alumina and zirconia were prepared by the impregnation method and calcined at 600 and 1000 ºC. Catalysts were characterized by BET measurements, XRD, XPS, O2-TPD and tested in methane combustion through temperature programmed surface reaction. Alumina supported catalysts were slightly more active than zirconia supported catalysts, but after initial heat treatment at 1000 ºC, zirconia supported palladium catalyst showed better performance above 500 ºC A pattern between temperature interval stability of PdOx species and activity was observed, where better PdOx stability was associated with more active catalysts.

Methane combustion kinetic rate constants determination: an ill-posed inverse problem analysis

Methane combustion was studied by the Westbrook and Dryer model. This well-established simplified mechanism is very useful in combustion science, for computational effort can be notably reduced. In the inversion procedure to be studied, rate constants are obtained from [CO] concentration data. However, when inherent experimental errors in chemical concentrations are considered, an ill-conditioned inverse problem must be solved for which appropriate mathematical algorithms are needed. A recurrent neural network was chosen due to its numerical stability and robustness. The proposed methodology was compared against Simplex and Levenberg-Marquardt, the most used methods for optimization problems.

Evaluation of the dioxin and furan formation thermodynamics in combustion processes of urban solid wastes

Specific combustion programs (Gaseq, Chemical equilibria in perfect gases, Chris Morley) are used to model dioxin and formation in the incineration processes of urban solid wastes. Thanks to these programs, it is possible to establish correlations with the formation mechanisms postulated in literature on the subject. It was found that minimum oxygen quantities are required to obtain a significant formation of these compounds and that more furans than dioxins are formed. Likewise, dioxin and furan formation is related to the presence of carbon monoxide, and dioxin and furan distribution among its different compounds depends on the chlorine and hydrogen relative composition. This is due to the fact that an increased chlorine availability leads to the formation of compounds bearing a higher chlorine concentration (penta-, hexa-, hepta-, and octachlorides), whereas an increased hydrogen availability leads to the formation of compounds bearing a lower chlorine number (mono, di-, tri-, and tetrachlorides).

Lanthanum based high surface area perovskite-type oxide and application in CO and propane combustion

The perovskite-type oxides using transition metals present a promising potential as catalysts in total oxidation reaction. The present work investigates the effect of synthesis by oxidant co-precipitation on the catalytic activity of perovskite-type oxides LaBO3 (B= Co, Ni, Mn) in total oxidation of propane and CO. The perovskite-type oxides were characterized by means of X-ray diffraction, nitrogen adsorption (BET method), thermo gravimetric and differential thermal analysis (ATG-DTA) and X-ray photoelectron spectroscopy (XPS). Through a method involving the oxidant co-precipitation it's possible to obtain catalysts with different BET surface areas, of 33-44 m²/g, according the salts of metal used. The characterization results proved that catalysts have a perovskite phase as well as lanthanum oxide, except LaMnO3, that presents a cationic vacancies and generation for known oxygen excess. The results of catalytic test showed that all oxides have a specific catalytic activity for total oxidation of CO and propane even though the temperatures for total conversion change for each transition metal and substance to be oxidized.

GRANULOMETRIC INFLUENCE ON THE COMBUSTION OF CHARCOAL FOR BARBECUE1

The present work analyzed characteristics of charcoal used for barbecue and mainly took interest in the influence of the granulometry in the combustion process. The material have been tested for four different grain size (8, 16, 32 and 50 mm) following a combustion test called combustion index (ICOMcv), which takes in consideration time processing, temperature generated and the mass consumed. The characterization of charcoal was done according to the following parameters, moisture, apparent density, grain density, volatile materials content, ash content, fixed carbon content and calorific value. The proofed charcoal presented standard indicators for use in barbecue and was noticed the relationship between granulometric analysis and the ICOMcv. The 16 mm grain size charcoal sample showed the best results for combustion. By contrast, the largest grain size sample presented lower results compared to the other samples. Thus, establishing unprecedented quantitative indicators in relation to those observed in practice, regarding the influence of grain size on the efficiency of combustion of the charcoal when used for barbecue.

Effect of different surface roughnesses on a turbulent boundary layer

The classical treatment of rough wall turbulent boundary layers consists in determining the effect the roughness has on the mean velocity profile. This effect is usually described in terms of the roughness function delta U+. The general implication is that different roughness geometries with the same delta U+ will have similar turbulence characteristics, at least at a sufficient distance from the roughness elements. Measurements over two different surface geometries (a mesh roughness and spanwise circular rods regularly spaced in the streamwise direction) with nominally the same delta U+ indicate significant differences in the Reynolds stresses, especially those involving the wall-normal velocity fluctuation, over the outer region. The differences are such that the Reynolds stress anisotropy is smaller over the mesh roughness than the rod roughness. The Reynolds stress anisotropy is largest for a smooth wall. The small-scale anisotropy and interniittency exhibit much smaller differences when the Taylor microscale Reynolds number and the Kolmogorov-normalized mean shear are nominally the same. There is nonetheless evidence that the small-scale structure over the three-dimensional mesh roughness conforms more closely with isotropy than that over the rod-roughened and smooth walls.

Modeling of turbulent flow through radial diffuser

The work considers the modeling of turbulent flow in radial diffuser with axial feeding. Due to its claimed capability to predict flow including features such as separation, curvature and adverse pressure gradient, the RNG k-epsilon model of Orzag et al. (1993) is applied in the present analysis. The governing equations are numerically solved using the finite volume methodology. Experiments were conducted to assess the turbulence model. Numerical results of pressure distribution on the front disk surface for different flow conditions when compared to the experimental data indicated that the RNG k-epsilon model is adequate to predict this class of flow.

Turbulent shallow-water model for orographic subgrid-scale perturbations

A parallel pseudo-spectral method for the simulation in distributed memory computers of the shallow-water equations in primitive form was developed and used on the study of turbulent shallow-waters LES models for orographic subgrid-scale perturbations. The main characteristics of the code are: momentum equations integrated in time using an accurate pseudo-spectral technique; Eulerian treatment of advective terms; and parallelization of the code based on a domain decomposition technique. The parallel pseudo-spectral code is efficient on various architectures. It gives high performance onvector computers and good speedup on distributed memory systems. The code is being used for the study of the interaction mechanisms in shallow-water ows with regular as well as random orography with a prescribed spectrum of elevations. Simulations show the evolution of small scale vortical motions from the interaction of the large scale flow and the small-scale orographic perturbations. These interactions transfer energy from the large-scale motions to the small (usually unresolved) scales. The possibility of including the parametrization of this effects in turbulent LES subgrid-stress models for the shallow-water equations is addressed.

An experimental/numerical study of the turbulent boundary layer development along a surface with a sudden change in roughness

A theory for the description of turbulent boundary layer flows over surfaces with a sudden change in roughness is considered. The theory resorts to the concept of displacement in origin to specify a wall function boundary condition for a kappa-epsilon model. An approximate algebraic expression for the displacement in origin is obtained from the experimental data by using the chart method of Perry and Joubert(J.F.M., vol. 17, pp. 193-122, 1963). This expression is subsequently included in the near wall logarithmic velocity profile, which is then adopted as a boundary condition for a kappa-epsilon modelling of the external flow. The results are compared with the lower atmospheric observations made by Bradley(Q. J. Roy. Meteo. Soc., vol. 94, pp. 361-379, 1968) as well as with velocity profiles extracted from a set of wind tunnel experiments carried out by Avelino et al.( 7th ENCIT, 1998). The measurements are found to be in good agreement with the theoretical computations. The skin-friction coefficient was calculated according to the chart method of Perry and Joubert(J.F.M., vol. 17, pp. 193-122, 1963) and to a balance of the integral momentum equation. In particular, the growth of the internal boundary layer thickness obtained from the numerical simulation is compared with predictions of the experimental data calculated by two methods, the "knee" point method and the "merge" point method.