Neste trabalho apresenta-se uma modelagem e a simulação de chamas difusivas turbulentas de etanol. A pesquisa trata da simulação da mistura molecular envolvendo reações químicas e combustão. Como os modelos de cinética química detalhada podem tornar-se computacionalmente proibitivos, por possuírem inúmeras reações e várias espécies, modelos cinéticos reduzidos são adotados. O mecanismo de oxidação do etanol utilizado possui 372 reações elementares e 56 espécies. Para diminuir a rigidez do sistema de equações rea- tivas resultantes, desenvolveu-se um mecanismo reduzido através do Método de Redução Sistemático, que usa as hipóteses de equilíbrio parcial e de regime permanente. A técnica Reaction Difusion Manifolds (REDIM), que aplica o conceito de variedade invariante, também foi implementada. A formulação Euleriana é utilizada para resolver as equações governantes da fase gasosa, que incluem as equações de Navier-Stokes, fração de mistura, fração mássica das espécies e temperatura. O efeito das gotas, fase líquida, é considerado pela introdução de termos fonte apropriados nas equações da fase gasosa. A Simulação em Grandes Escalas é utilizada para representar o fluxo turbulento com o modelo submalha de Smagorinsky para modelar a viscosidade turbulenta. Na simulação numérica adota-se o método de diferenças finitas com um sistema não oscilatório do tipo Total Variation Diminishing (TVD). O domínio é um queimador tridimensional com malha não uniforme para garantir a eficiência e precisão nos resultados em regiões onde o refinamento faz-se necessário. Para validar o modelo, além dos resultados numéricos para chamas difusivas de etanol, também realiza-se testes numéricos para chamas difusivas de metano e metanol, e os resultados obtidos comparam favoravelmente com dados encontrados na literatura. / This work presents the modeling and simulation of turbulent diffusion flames of etha- nol. The study addresses the simulation of the molecular mixing, chemical reactions and combustion. Since detailed chemical kinetics models may be computationally prohibitive, reduced kinetic models are adopted. The ethanol oxidation mechanism consists of 372 elementary reactions and 56 species. To decrease the stiffness of the reactive system of equations, a reduced mechanism is developed using the Systematic Reduction Method, based on the partial equilibrium and steady-state approximations. The Reaction Diffusion Manifolds (REDIM) technique, which applies the concept of invariant manifolds to treat the influence of the transport processes on the reduced model, is also employed. The Eule- rian formulation is used to solve the governing equations of the gas phase, which includes the Navier-Stokes, mixture fraction, species mass fraction and temperature equations. The effect of the drops, the liquid phase, is considered by introducing appropriate source terms in the equations of the gas phase. Large-Eddy Simulation is used to represent the turbulent flow with the Smagorinsky model for the turbulent viscosity. The numerical simulations are carried out using the finite difference method with a non oscillatory Total Variation Diminishing (TVD) scheme. The burner is a three-dimensional domain with nonuniform mesh to ensure efficiency and accuracy in regions where mesh refinement is necessary. To validate the model, besides the numerical results for diffusive flames of ethanol, numerical tests for methane and methanol diffusive flames are also carried out and the results compare favourably with data in the literature.

Neste trabalho apresenta-se uma modelagem e a simulação de chamas difusivas turbulentas de etanol. A pesquisa trata da simulação da mistura molecular envolvendo reações químicas e combustão. Como os modelos de cinética química detalhada podem tornar-se computacionalmente proibitivos, por possuírem inúmeras reações e várias espécies, modelos cinéticos reduzidos são adotados. O mecanismo de oxidação do etanol utilizado possui 372 reações elementares e 56 espécies. Para diminuir a rigidez do sistema de equações rea- tivas resultantes, desenvolveu-se um mecanismo reduzido através do Método de Redução Sistemático, que usa as hipóteses de equilíbrio parcial e de regime permanente. A técnica Reaction Difusion Manifolds (REDIM), que aplica o conceito de variedade invariante, também foi implementada. A formulação Euleriana é utilizada para resolver as equações governantes da fase gasosa, que incluem as equações de Navier-Stokes, fração de mistura, fração mássica das espécies e temperatura. O efeito das gotas, fase líquida, é considerado pela introdução de termos fonte apropriados nas equações da fase gasosa. A Simulação em Grandes Escalas é utilizada para representar o fluxo turbulento com o modelo submalha de Smagorinsky para modelar a viscosidade turbulenta. Na simulação numérica adota-se o método de diferenças finitas com um sistema não oscilatório do tipo Total Variation Diminishing (TVD). O domínio é um queimador tridimensional com malha não uniforme para garantir a eficiência e precisão nos resultados em regiões onde o refinamento faz-se necessário. Para validar o modelo, além dos resultados numéricos para chamas difusivas de etanol, também realiza-se testes numéricos para chamas difusivas de metano e metanol, e os resultados obtidos comparam favoravelmente com dados encontrados na literatura. / This work presents the modeling and simulation of turbulent diffusion flames of etha- nol. The study addresses the simulation of the molecular mixing, chemical reactions and combustion. Since detailed chemical kinetics models may be computationally prohibitive, reduced kinetic models are adopted. The ethanol oxidation mechanism consists of 372 elementary reactions and 56 species. To decrease the stiffness of the reactive system of equations, a reduced mechanism is developed using the Systematic Reduction Method, based on the partial equilibrium and steady-state approximations. The Reaction Diffusion Manifolds (REDIM) technique, which applies the concept of invariant manifolds to treat the influence of the transport processes on the reduced model, is also employed. The Eule- rian formulation is used to solve the governing equations of the gas phase, which includes the Navier-Stokes, mixture fraction, species mass fraction and temperature equations. The effect of the drops, the liquid phase, is considered by introducing appropriate source terms in the equations of the gas phase. Large-Eddy Simulation is used to represent the turbulent flow with the Smagorinsky model for the turbulent viscosity. The numerical simulations are carried out using the finite difference method with a non oscillatory Total Variation Diminishing (TVD) scheme. The burner is a three-dimensional domain with nonuniform mesh to ensure efficiency and accuracy in regions where mesh refinement is necessary. To validate the model, besides the numerical results for diffusive flames of ethanol, numerical tests for methane and methanol diffusive flames are also carried out and the results compare favourably with data in the literature.

Neste trabalho apresenta-se uma modelagem e a simulação de chamas difusivas turbulentas de etanol. A pesquisa trata da simulação da mistura molecular envolvendo reações químicas e combustão. Como os modelos de cinética química detalhada podem tornar-se computacionalmente proibitivos, por possuírem inúmeras reações e várias espécies, modelos cinéticos reduzidos são adotados. O mecanismo de oxidação do etanol utilizado possui 372 reações elementares e 56 espécies. Para diminuir a rigidez do sistema de equações rea- tivas resultantes, desenvolveu-se um mecanismo reduzido através do Método de Redução Sistemático, que usa as hipóteses de equilíbrio parcial e de regime permanente. A técnica Reaction Difusion Manifolds (REDIM), que aplica o conceito de variedade invariante, também foi implementada. A formulação Euleriana é utilizada para resolver as equações governantes da fase gasosa, que incluem as equações de Navier-Stokes, fração de mistura, fração mássica das espécies e temperatura. O efeito das gotas, fase líquida, é considerado pela introdução de termos fonte apropriados nas equações da fase gasosa. A Simulação em Grandes Escalas é utilizada para representar o fluxo turbulento com o modelo submalha de Smagorinsky para modelar a viscosidade turbulenta. Na simulação numérica adota-se o método de diferenças finitas com um sistema não oscilatório do tipo Total Variation Diminishing (TVD). O domínio é um queimador tridimensional com malha não uniforme para garantir a eficiência e precisão nos resultados em regiões onde o refinamento faz-se necessário. Para validar o modelo, além dos resultados numéricos para chamas difusivas de etanol, também realiza-se testes numéricos para chamas difusivas de metano e metanol, e os resultados obtidos comparam favoravelmente com dados encontrados na literatura. / This work presents the modeling and simulation of turbulent diffusion flames of etha- nol. The study addresses the simulation of the molecular mixing, chemical reactions and combustion. Since detailed chemical kinetics models may be computationally prohibitive, reduced kinetic models are adopted. The ethanol oxidation mechanism consists of 372 elementary reactions and 56 species. To decrease the stiffness of the reactive system of equations, a reduced mechanism is developed using the Systematic Reduction Method, based on the partial equilibrium and steady-state approximations. The Reaction Diffusion Manifolds (REDIM) technique, which applies the concept of invariant manifolds to treat the influence of the transport processes on the reduced model, is also employed. The Eule- rian formulation is used to solve the governing equations of the gas phase, which includes the Navier-Stokes, mixture fraction, species mass fraction and temperature equations. The effect of the drops, the liquid phase, is considered by introducing appropriate source terms in the equations of the gas phase. Large-Eddy Simulation is used to represent the turbulent flow with the Smagorinsky model for the turbulent viscosity. The numerical simulations are carried out using the finite difference method with a non oscillatory Total Variation Diminishing (TVD) scheme. The burner is a three-dimensional domain with nonuniform mesh to ensure efficiency and accuracy in regions where mesh refinement is necessary. To validate the model, besides the numerical results for diffusive flames of ethanol, numerical tests for methane and methanol diffusive flames are also carried out and the results compare favourably with data in the literature.

Soot is a carbon particulate formed as a result of the combustion of fossil fuels. Due to the health hazard posed by the carbon particulate, government agencies have applied strict regulations to control soot emissions from road vehicles, airplanes, and industrial plants. Thus, understanding soot formation and evolution is critical. Practical combustion devices operate at high pressure and in the turbulent regime. Elevated pressures and turbulence on soot formation significantly and fundamental understanding of these complex interactions is still poor. In this study, the effects of pressure and turbulence on soot formation and growth are investigated numerically. As the first step, the evolution of the particle size distribution function (PSDF) and soot particles morphology are investigated in turbulent non-premixed flames. A Direct Simulation Monte Carlo (DSMC) code is developed and used. The stochastic reactor describes the evolution of soot in fluid parcels following Lagrangian trajectories in a turbulent flow field. The trajectories are sampled from a Direct Numerical Simulation (DNS) of an n-heptane turbulent non-premixed flame. Although individual trajectories display strong bimodality as in laminar flames, the ensemble-average PSDF possesses only one mode and a broad tail, which implies significant polydispersity induced by turbulence. Secondly, the effect of the flow and mixing fields on soot formation at atmospheric and elevated pressures is investigated in coflow laminar diffusion flames. The experimental observation and the numerical prediction of the spatial distribution are in good agreement. Based on the common scaling methodology of the flames (keeping the Reynolds number constant), the scalar dissipation rate decreases as pressure increases, promoting the formation of PAH species and soot. The decrease of the scalar dissipation rate significantly contributes to soot formation occurring closer to the nozzle and outward on the flames wings as pressure increases. The scaling of the scalar dissipation rate is not straightforward due to buoyancy effects. Finally, a new scaling approach of the flame at different pressures is introduced. In this approach, both Reynolds number and Grashof number are kept constant so that the effect of gravity is the same at all pressures. In order to keep Gr constant, this requires the diameter of the nozzle to be changed as pressures vary. This approach guarantees a similar non-dimensional flow field at all pressures and rules out the effect of hydrodynamics and mixing, so that only the effect of chemical kinetics on soot formation can be studied.

Propulsion engine combustor design and analysis require experimentally verified data on the chemical kinetics of limiting fuel combustion rates. Among the important data is the combustion extinction limit as measured by the maximum global strain rate on a laminar, counterflow, non-premixed flame. The extinction limit relates to the ability to maintain combustor operation, and the extinction limit data for pure fuel versus air systems provide a relative reactivity scale for use in the design of flame holders. Extinction limit data were obtained for nine fuels by means of a laminar flame experiment using an opposed jet burner (OJB). The OJB consists of two axi-symmetric tubes (for fuel and oxidizer separately), which produce a flat, disk-like, counterflow diffusion flame. This paper presents results of experiments conducted in an OJB that measured extinction limits at one atmosphere for vaporized n-heptane, the Air Force-developed fuels JP-7, and JP-10, as well as methane, ethane, ethylene, propane, butane, and hydrogen. In hypersonic aircraft development it is desirable to design a Scramjet engine that is operated on hydrocarbon fuel, particularly JP-7 due to its distinct properties. This study provides key data for JP-7, for which very limited information previously existed. The interest in n-heptane is twofold. First, it has undergone a significant amount of previous flame structure and extinction limit study. Second, n-heptane (C7H16) is a pure substance, and therefore does not vary in composition, as does JP-7, which is a variable mixture of several different hydrocarbons. These two facts allow a baseline to be established by comparing the new OJB results to those previously taken. Additionally, the existing data for n-heptane, for mixtures up to 26 mole percent in nitrogen, is extended to 100% n-heptane, reaching an asymptotic limit. Extinction limit data for the two fuels are given with a comparison to hydrogen and several other gaseous hydrocarbon fuels. Complete experimental results are included. / Master of Science

A low-order discrete dynamical system (DDS) for finite-rate chemistry of H2-air combustion is derived in 3D. Fourier series with a single wavevector are employed to represent dependent variables of subgrid-scale (SGS) behaviors for applications to large-eddy simulation (LES). A Galerkin approximation is applied to the governing equations for comprising the DDS. Regime maps are employed to aid qualitative determination of useful values for bifurcation parameters of the DDS. Both isotropic and anisotropic assumptions are employed when constructing regime maps and studying bifurcation parameters sequences. For H2-air reactions, two reduced chemical mechanisms are studied via the DDS. As input to the DDS, physical quantities from experimental turbulent flow are used. Numerical solutions consisting of time series of velocities, species mass fractions, temperature, and the sum of mass fractions are analyzed. Numerical solutions are compared with experimental data at selected spatial locations within the experimental flame to check whether this model is suitable for an entire flame field. The comparisons show the DDS can mimic turbulent combustion behaviors in a qualitative sense, and the time-averaged computed results of some species are quantitatively close to experimental data.

Scientific research in areas of physics, chemistry, and biology traditionally depends purely on experimental and theoretical methods. Recently numerical simulation is emerging as the third way of science discovery beyond the experimental and theoretical approaches. This work describes some general procedures in numerical computation, and presents several applications of numerical modeling in bioheat transfer and biomechanics, jet diffusion flame, and bio-molecular interactions of proteins in blood circulation. A three-dimensional (3D) multilayer model based on the skin physical structure is developed to investigate the transient thermal response of human skin subject to external heating. The temperature distribution of the skin is modeled by a bioheat transfer equation. Different from existing models, the current model includes water evaporation and diffusion, where the rate of water evaporation is determined based on the theory of laminar boundary layer. The time-dependent equation is discretized using the Crank-Nicolson scheme. The large sparse linear system resulted from discretizing the governing partial differential equation is solved by GMRES solver. The jet diffusion flame is simulated by fluid flow and chemical reaction. The second-order backward Euler scheme is applied for the time dependent Navier-Stokes equation. Central difference is used for diffusion terms to achieve better accuracy, and a monotonicity-preserving upwind difference is used for convective ones. The coupled nonlinear system is solved via the damped Newton's method. The Newton Jacobian matrix is formed numerically, and resulting linear system is ill-conditioned and is solved by Bi-CGSTAB with the Gauss-Seidel preconditioner. A novel convection-diffusion-reaction model is introduced to simulate fibroblast growth factor (FGF-2) binding to cell surface molecules of receptor and heparan sulfate proteoglycan and MAP kinase signaling under flow condition. The model includes three parts: the flow of media using compressible Navier-Stokes equation, the transport of FGF-2 using convection-diffusion transport equation, and the local binding and signaling by chemical kinetics. The whole model consists of a set of coupled nonlinear partial differential equations (PDEs) and a set of coupled nonlinear ordinary differential equations (ODEs). To solve the time-dependent PDE system we use second order implicit Euler method by finite volume discretization. The ODE system is stiff and is solved by an ODE solver VODE using backward differencing formulation (BDF). Findings from this study have implications with regard to regulation of heparin-binding growth factors in circulation.

Biofuels are of particular interest as they have the potential to reduce our dependence on petroleum-derived fuels for transportation. 1-Hexanol is a promising renewable long chain alcohol that can be used in conventional fuel blends or as a cosolvent for biodiesel mixtures. However, the fundamental combustion properties of 1-hexanol have not been fully characterized in the literature. Thus, new experimental results, consisting of temperature and concentration profiles of stable species were obtained for the oxidation of 1-hexanol generated in an opposed-flow diffusion flame at 0.101 MPa. The kinetic model consists of 361 chemical species and 2687 chemical reactions (most of them reversible). This experimental data were compared to the predicted values of a detailed chemical kinetic model proposed in literature to study the combustion of 1-hexanol. Reaction pathway and sensitivity analyses were performed to interpret the results. In addition, several improvements were investigated to optimize the proposed chemical kinetic mechanism.

Biofuels are of particular interest as they have the potential to reduce our dependence on petroleum-derived fuels for transportation. 1-Hexanol is a promising renewable long chain alcohol that can be used in conventional fuel blends or as a cosolvent for biodiesel mixtures. However, the fundamental combustion properties of 1-hexanol have not been fully characterized in the literature. Thus, new experimental results, consisting of temperature and concentration profiles of stable species were obtained for the oxidation of 1-hexanol generated in an opposed-flow diffusion flame at 0.101 MPa. The kinetic model consists of 361 chemical species and 2687 chemical reactions (most of them reversible). This experimental data were compared to the predicted values of a detailed chemical kinetic model proposed in literature to study the combustion of 1-hexanol. Reaction pathway and sensitivity analyses were performed to interpret the results. In addition, several improvements were investigated to optimize the proposed chemical kinetic mechanism.

No description available.