Albino J. K. Leiroz

ON THE SOLUTION OF NONLINEAR ELLIPTIC CONVECTION-DIFFUSION PROBLEMS THROUGH THE INTEGRAL TRANSFORM METHOD

The hybrid numerical-analytical solution of nonlinear elliptic convection-diffusion problems is investigated through extension of the ideas in the generalized integral transform technique. An application is selected to illustrate the convergence characteristics of the proposed eigenfunction expansion approach, for different values of the parameters that govern the relative importance of convection and diffusion effects.

Heat transfer coefficient estimation of an internal combustion engine using particle filters

The continuous growth of the worldwide vehicle fleet is leading to many private initiatives and governmental policies for the achievement of lower pollutant and greenhouse gas emissions through energetic efficiency improvement. The in-cylinder heat transfer has been generally recognised as a major factor influencing internal combustion engines efficiency and exhaust emissions. Therefore, the analysis of in-cylinder heat transfer is of importance for fuel economy, as well as for environmental preservation. In the present paper, the use of particle filters applied on the time-dependent heat transfer coefficient estimation of a combustion process in a spark-ignition internal combustion engine is presented. The combustion process was modelled as a transient zero-dimensional process based on the First Law of Thermodynamics for a perfect gas, and the fuel burned fraction was modelled through a Wiebe’s function model. Results with different measurement frequencies and errors are available, using a sample importance resampling filter, showing a very good estimate, even for initial guesses far away from the real value of the unknown function.

Interaction Effects During Combustion of Linear Arrays of Gaseous Fuel Pockets

The numerical solution for the combustion of an infinite linear array of dense fuel gas pockets in a quiescent ambient is discussed in the present work. Fuel mass, flame, and gas pocket shape behaviors are analyzed in order to quantify the interference effects. The combustion process is considered isobaric. The model is based on mass, momentum, energy, and species conservation equations and considers the simple chemical reaction mechanism and ideal gas behavior. Coupling potentials are used in the solution of the energy and species conservations equations. The thermophysical properties, except the density, are assumed constant. The finite-volume method is used for the numerical solution, using a generalized system of coordinates and a nonstaggered grid. The SIMPLEC algorithm is applied to solve the modified pressure-velocity coupling. The flame and gas pocket morphological evolutions as well as the transient fuel consumption and the flame position behaviors are presented. The effects of the initial fuel and oxidant temperatures, of the interpocket distance, of the stoichiometric condition, of the heat of reaction, and of the mixture thermophysical properties on the combustion process are considered. Results show that the interactive effects on gas pocket linear array combustion are relevant only for small interpocket distances. Results also show flame shape temporal evolutions that indicate an oscillatory behavior dependent on the gas pocket burning conditions.

Exergetic Analysis of Cogeneration Plants Through Integration of Internal Combustion Engine and Process Simulators

Internal combustion engines (ICEs) have been used in power generation even before they were massively employed for transportation. Their high reliability, excellent power-to-weight ratio, and thermal efficiency have made them a competitive choice as main energy converters in small to medium-sized power plants. Process simulators can model ICE-powered energy plants with limited depth due to the highly simplified engine models used, which require the description of individual energy and mass flows entering or leaving the engine. ICE models available in process simulators are therefore not predictive but merely descriptive representations of the engines. Because the combustion process within the ICE is typically the main cause of exergy destruction in ICE-powered energy plants, a better understanding of the global effects of different engine parameters is desirable. This article presents and exploits the integration of an internal combustion engine simulator with a process simulator, so as to obtain a novel, fully coupled simulation platform to analyze the performance of ICE-based power plants. A simulation model of an actual cogeneration plant is used as an example for the application of the proposed computational methodology. The results show that by manipulating engine mapping parameters the plant overall efficiency can be improved.

Global warming description using Daisyworld model with greenhouse gases

Daisyworld is an archetypal model of the earth that is able to describe the global regulation that can emerge from the interaction between life and environment. This article proposes a model based on the original Daisyworld considering greenhouse gases emission and absorption, allowing the description of the global warming phenomenon. Global and local analyses are discussed evaluating the influence of greenhouse gases in the planet dynamics. Numerical simulations are carried out showing the general qualitative behavior of the Daisyworld for different scenarios that includes solar luminosity variations and greenhouse gases effect. Nonlinear dynamics perspective is of concern discussing a way that helps the comprehension of the global warming phenomenon.

Analysis of Wood Biomass in Bubbling Fluidized Bed Reactors

This article analysis the computational simulation of woods gasification in a bubbling fluidized bed reactor. Most articles about this topic, on homogenous reactions, don’t consider methane reforming. However, this article has taken this into consideration in the process of gasification. The bubbling fluidized bed reactor was used in the simulation, in which the advantages of a good mixture is presented, one which provides high rates of mass and heat transfer. The gas-solid flow that occurs in this reactor was described through mass, energy, momentum, and chemical species balances. The model used for the simulation was the computational fluid dynamics (CFD), by means of an open-source program named MFIX (Multiphase Flow with Interphase eXchange). It is concluded that methane reforming is important in the process of gasification.

Transient gas phase interaction effects during droplet-stream combustion

Gas-phase transient effects during the combustion of an infinite linear array of droplets are studied in the limit of infinite Damkoler number and in the absence of surrounding convective effects. The present study stems from the quantification of truncation-distance effects on the droplet mass vaporization rate, flame position and flame shape in quasi-steady numerical simulations. The solution domain is initially split into near and far-field subdomains. Within each subdomain, analytical grid generation techniques are applied allowing the development of appropriate finite-difference expressions, the control of grid point distribution and the treatment of outflow boundary conditions. The interdroplet distance effect is studied and results for the droplet mass vaporization rate and flame behavior are presented. The results show the existence of different flame regimes ranging from isolated to merged flame conditions and similar vaporization rate evolution for different interdroplet distances.