Diagnostics for the Combustion Science Workbench

As the cost of computers declines relative to outfitting and maintaining laser spectroscopy laboratories, computers will account for an increasing proportion of the research conducted in fundamental combustion science. W. C. Gardiner foresaw that progress will be limited by the ability to understand the implications of what has been computed and to draw inferences about the elementary components of the combustion models. Yet the diagnostics that are routinely applied to computer experiments have changed little from the sensitivity analyses included with the original CHEMKIN software distribution. This paper describes some diagnostics capabilities that may be found on the virtual combustion science workbench of the future. These diagnostics are illustrated by some new results concerning which of the hydrogen/oxygen chain branching reactions actually occur in flames, the increased formation of NOx in wrinkled flames versus flat flames, and the adequacy of theoretical predictions of the effects of stretch. Several areas are identified where work is needed, including the areas of combustion chemistry and laser diagnostics, to make the virtual laboratory a reality

Numerical Simulation of a Laboratory-Scale Turbulent SlotFlame

We present three-dimensional, time-dependent simulations ofthe flowfield of a laboratory-scale slot burner. The simulations areperformed using an adaptive time-dependent low Mach number combustionalgorithm based on a second-order projection formulation that conservesboth species mass and total enthalpy. The methodology incorporatesdetailed chemical kinetics and a mixture model for differential speciesdiffusion. Methane chemistry and transport are modeled using the DRM-19mechanism along with its associated thermodynamics and transportdatabases. Adaptive mesh refinementdynamically resolves the flame andturbulent structures. Detailedcomparisons with experimental measurementsshow that the computational results provide a good prediction of theflame height, the shape of the time-averaged parabolic flame surfacearea, and the global consumption speed (the volume per second ofreactants consumed divided by the area of the time-averaged flame). Thethickness of the computed flamebrush increases in the streamwisedirection, and the flamesurface density profiles display the same generalshapes as the experiment. The structure of the simulated flame alsomatches the experiment; reaction layers are thin (typically thinner than1 mm) and the wavelengths of large wrinkles are 5--10 mm. Wrinklesamplify to become long fingers of reactants which burn through at a neckregion, forming isolated pockets of reactants. Thus both the simulatedflame and the experiment are in the "corrugated flameletregime.

SPIN (Version 3. 83): A Fortran program for modeling one-dimensional rotating-disk/stagnation-flow chemical vapor deposition reactors

In rotating-disk reactor a heated substrate spins (at typical speeds of 1000 rpm or more) in an enclosure through which the reactants flow. The rotating disk geometry has the important property that in certain operating regimes{sup 1} the species and temperature gradients normal to the disk are equal everywhere on the disk. Thus, such a configuration has great potential for highly uniform chemical vapor deposition (CVD),{sup 2--5} and indeed commercial rotating-disk CVD reactors are now available. In certain operating regimes, the equations describing the complex three-dimensional spiral fluid motion can be solved by a separation-of-variables transformation{sup 5,6} that reduces the equations to a system of ordinary differential equations. Strictly speaking, the transformation is only valid for an unconfined infinite-radius disk and buoyancy-free flow. Furthermore, only some boundary conditions are consistent with the transformation (e.g., temperature, gas-phase composition, and approach velocity all specified to be independent of radius at some distances above the disk). Fortunately, however, the transformed equations will provide a very good practical approximation to the flow in a finite-radius reactor over a large fraction of the disk (up to {approximately}90% of the disk radius) when the reactor operating parameters are properly chosen, i.e, high rotation rates. In the limit of zero rotation rate, the rotating disk flow reduces to a stagnation-point flow, for which a similar separation-of-variables transformation is also available. Such flow configurations ( pedestal reactors'') also find use in CVD reactors. In this report we describe a model formulation and mathematical analysis of rotating-disk and stagnation-point CVD reactors. Then we apply the analysis to a compute code called SPIN and describe its implementation and use. 31 refs., 4 figs

Diagnostics for the Combustion Science Workbench

As the cost of computers declines relative to outfitting and maintaining laser spectroscopy laboratories, computers will account for an increasing proportion of the research conducted in fundamental combustion science. W. C. Gardiner foresaw that progress will be limited by the ability to understand the implications of what has been computed and to draw inferences about the elementary components of the combustion models. Yet the diagnostics that are routinely applied to computer experiments have changed little from the sensitivity analyses included with the original CHEMKIN software distribution. This paper describes some diagnostics capabilities that may be found on the virtual combustion science workbench of the future. These diagnostics are illustrated by some new results concerning which of the hydrogen/oxygen chain branching reactions actually occur in flames, the increased formation of NOx in wrinkled flames versus flat flames, and the adequacy of theoretical predictions of the effects of stretch. Several areas are identified where work is needed, including the areas of combustion chemistry and laser diagnostics, to make the virtual laboratory a reality.

AURORA: A FORTRAN program for modeling well stirred plasma and thermal reactors with gas and surface reactions

The AURORA Software is a FORTRAN computer program that predicts the steady-state or time-averaged properties of a well mixed or perfectly stirred reactor for plasma or thermal chemistry systems. The software was based on the previously released software, SURFACE PSR which was written for application to thermal CVD reactor systems. AURORA allows modeling of non-thermal, plasma reactors with the determination of ion and electron concentrations and the electron temperature, in addition to the neutral radical species concentrations. Well stirred reactors are characterized by a reactor volume, residence time or mass flow rate, heat loss or gas temperature, surface area, surface temperature, the incoming temperature and mixture composition, as well as the power deposited into the plasma for non-thermal systems. The model described here accounts for finite-rate elementary chemical reactions both in the gas phase and on the surface. The governing equations are a system of nonlinear algebraic relations. The program solves these equations using a hybrid Newton/time-integration method embodied by the software package TWOPNT. The program runs in conjunction with the new CHEMKIN-III and SURFACE CHEMKIN-III packages, which handle the chemical reaction mechanisms for thermal and non-thermal systems. CHEMKIN-III allows for specification of electron-impact reactions, excitation losses, and elastic-collision losses for electrons

OPPDIF: A Fortran program for computing opposed-flow diffusion flames

OPPDIF is a Fortran program that computes the diffusion flame between two opposing nozzles. A similarity transformation reduces the two-dimensional axisymmetric flow field to a one-dimensional problem. Assuming that the radial component of velocity is linear in radius, the dependent variables become functions of the axial direction only. OPPDIF solves for the temperature, species mass fractions, axial and radial velocity components, and radial pressure gradient, which is an eigenvalue in the problem. The TWOPNT software solves the two-point boundary value problem for the steady-state form of the discretized equations. The CHEMKIN package evaluates chemical reaction rates and thermodynamic and transport properties