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CFD in IC Engines

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Computational Fluid Dynamics for Internal Combustion Engines

Introduction

Computational Fluid Dynamics (CFD) has become an established tool for the design and understanding of physical systems including fluid flows and combustion processes. Main benefit from numerical simulations in Internal Combustion (IC) Engines is the possibility to conduct parametric studies and investigate the effect of various factors on engine operation, power output and emissions formation. In order to successfully simulate the processes that take place inside an IC engine, several models are needed to handle every physical or chemical process, such as fuel injection, droplet breakup and collisions, evaporation, ignition, combustion and heat release.

Background Information

The governing equations for Newtonian fluid dynamics, the unsteady Navier-Stokes equations, have been known for more than 150 years. However, the development of reduced forms of these equations is still an active area of research. For non-Newtonian fluid dynamics, chemically reacting flows and two-phase flows the theoretical development is at a less advanced stage.

The steady improvement in the speed of computers and the memory size since the 1950s has led to the emergence of Computational Fluid Dynamics. This branch of fluid dynamics complements experimental and theoretical fluid dynamics by providing an alternative cost-effective means of simulating real flows. As such, it offers the means of testing theoretical advances for conditions unavailable experimentally.

Perhaps the most important reason for the growth of CFD is that for much mainstream flow simulations, CFD is significantly cheaper than physical experimentation (such as wind-tunnel testing) and will become even more so in the future. Improvements in computer hardware perormance have occured hand in hand with a decreasing hardware cost. In addition, improvements in the efficiency of computational algorithms for a given problem make CFD increasingly cost-effective [1].

Modeling IC Engines

A very powerful tool for CFD simulations in IC engines is the numerical code KIVA that has been developed at the Los Alamos National Laboratory. The original KIVA program was publicly released in 1985 and was replaced by the improved version KIVA-II in 1989 [2]. These earlier versions were performing quite good with confined in-cylinder flows and a variety of open combustion systems, but were rather inefficient when applied to complex geometries, such as long transfer ports or die-sel pre-chambers. KIVA-3, released in 1993 [3], has been improved by using block-structured meshes, as well as by reducing the computational time, by handling the data storage and boundary conditions in a more sophisticated and efficient way. KIVA-3V, made publicly available in 1997 [4], retains all the features of previous versions, while offering the possibility to model intake and exhaust valves, making use of a moving mesh.

Other commercially available codes for CFD calculations in IC engines include AVL-FIRE, Fluent and STAR-CD.

References

1. Fletcher, C.A.J., "Computational Techniques for Fluid Dynamics", vol. 1, Springer, 2nd ed., 1990
2. Amsden A.A., O’Rourke P.J., Butler T.D., “KIVA II – A Computer Program for Chemically Reactive Flows with Sprays”, Los Alamos National Laboratory LA-11560-MS, 1989
3. Amsden A.A., “KIVA-3: A KIVA Program with Block-Structured Mesh for Complex Geometries”, Los Alamos National Laboratory LA-12503-MS, 1993
4. Amsden A.A., “KIVA-3V: A Block-Structured KIVA Program for Engines with Vertical or Canted Valves”, Los Alamos National Laboratory LA-13313-MS, July 1997