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Research - Engines and Burners

   

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Engines and Burners

The legislation for reduced emissions and particulates, the exploration of new fuels and engine designs and the competitive need for increased efficiency and performance are challenging the entire engine design community. At this time of great need and increased competition, the use of computational modeling is coming of age and providing many design groups with a competitive edge. As a way of an introduction, the following is a list of broad areas in which modeling has proven useful.

As a design tool with minimal experimental support. In a few areas, modeling accuracy and capability have sufficiently evolved such that validation by experiments it is no longer necessary. The premiere example is the three-dimensional simulation of air induction, and the consequent prediction of the flow at time of combustion. Current capabilities have evolved to treat the complexities of engine geometries, most notably for valves and intake manifolds. Simulations can be quickly executed, and many configurations can be examined.

As an interpolative design tool with experimental validation. Often there is sufficient uncertainty in the accuracy of the models, such that experiments are required for validation. But once validated, the models can be used to examine the effects of variations in operating conditions, geometry, and fuels on engine performance or emissions, to within the regime of validation. The thermodynamic or zero-dimensional models have long proven their utility in this area. Similarly, multi-dimensional simulation codes are beginning to contribute equally to issues such as combustion timing, fuel composition or injection history.

As an analysis tool in the interpretation of complex experiments. One of the most rewarding applications of modeling is the integration of experiments and computational analysis. Once a simulation is validated with measurable experimental results, a greater understanding of engine phenomena can be inferred from the detailed information obtainable from computational results.

As an explorative tool for alternative engine designs. Many alternative, but promising, engine designs can be initially investigated by using computational modeling, without the cost of expensive prototypes. Experimental validation can then be applied once the possibilities for a design or modification are isolated.

As a developmental tool for improved physical or numerical submodels. A continual challenge for developers of the engine modeling capability is the goal of an accurate solution in a short time, requiring minimal computer resources. For a previously validated simulation capability, the results of more accurate, faster or more memory-efficient physical or numerical submodels can be compared to prior computational results.

The above is from the Preface of Modeling in Diesel and SI Engines,
SAE Publication SP-1123, N. L Johnson and Y. Takagi, editors.

Perspective on the history of engine modeling in T-3
Reactive flow and combustion modeling of fully miscible species is the area of broadest use of simulation codes from T-3 and possibly from Los Alamos. Currently these are represented by the KIVA family of codes [Amsden, 1993] [Amsden et al, 1989].

The KIVA codes are in worldwide useby industry, academia, and government laboratories. Their popularity as research tools [Amsden et al, 1993], primarily because of the availability of the source code and of thier unique treatment of sprays- now generally considered a worldwide standard.

Although the intended applications are to flow and combustion modeling in spark-ignition and diesel engines and gas turbines (as in Fig. 3.1-1), the extreme versatility and range of features have made KIVA programs attractive to a variety of non-engine applications as well. These range in scale from proposed 500-foot-high convection towers with water sprays that clean and cool the air in polluted urban areas, down to modeling silicon dioxide condensation in high pressure oxidation chambers used in the production of microchip wafers. Other applications have included the analysis of flows in automotive catalytic converters, power plant smokestack cleaning, pyrolytic treatment of biomass, design of fire suppression systems, pulsed detonation propulsion systems, stationary burners, aerosol dispersion, and design of heating, ventilation, and air conditioning systems. A complete history of KIVA as a paradigm of technology transfer from the government laboratories to industry can be found in [Amsden et al, 1993].

The current version of KIVA-3 uses an unstructured mesh of hexahedrons that are groups of logical blocks of mesh and an all-speed ALE formulation from the SALE heritage. Because of the ability to model opening and closing of ports and valves, connectivity of the mesh can change during the simulation. This is a unique feature of the currently active codes in T-3 (also see CAVEAT-GT below). KIVA is also unique in that it contains a Lagrangian particle treatment of liquid spays as originally proposed by Dukowicz [Dukowicz, 1980]. The current spray model includes breakup, collisions and evaporation, coupled with the turbulent gas field. This model is inherently stochastic, in contrast to the deterministic nature of all other T-3 CFD codes, and only produces an average solution for a large number of particles. The transport and chemistry equations can treat an arbitrary number of species and reactions, both kinetic and equilibrium. Mixing-controlled combustion that works in conjunction with the k-e turbulence model and a soot model are provided.

Parallel with the effort to continue the maturation of KIVA-3, future versions of KIVA are being developed. These codes use largely the same numerics as KIVA-3 but address the requirements of parallel computer architectures and requirements of modern mesh generation codes. KIVA-F90 is a complete rewrite of KIVA-II using Fortran 90 and executes on workstations, massively parallel architectures, and supercomputers without modification. KIVA-AC, just now under development, is an unstructured mesh version of KIVA-F90 that will support combinations of tetrahedrons and hexahedrons.


Los Alamos Engines and Burners Projects
All of the filled circles are linkable projects.
All of the empty circles are navigational guides.
 

  • Sprays
  • Valves and ports
  • Diesel Engine Port Flow
  • High Power Density

Questions? Contact us!

This is from "The Legacy and Future of CFD at Los Alamos" (LAUR#LA-UR-1426)(365Kb pdf file)


 

 

 

 

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