A Comparison of Boundary Layer Treatments for Heat Transfer in IC Engines 900252
Three different models, the law-of-the-wall, a modified law-of-the-wall, and an approximate one-dimensional solution to the energy equation are compared for the spatially-resolved prediction of engine heat tranfer. The multidimensional hydrodynamic code KIVA is used for the fluid mechanic simulation. Two different engine geometries are studied; one being a pancake-shaped chamber, and the other a bowl-in-piston geometry. The comparisons are done for a range of initial conditions of gas flow. Rates-of-pressure-rise were also varied to represent rates typical of those encountered in motored engines, and those found in fired engines.
Comparisons with experimental results show that the heat transfer predictions using the law-of-the-wall may be in error when source terms such as the transient, work and chemical energy terms have a significant effect in determining the temperature profile in the boundary layer. Modified wall function and approximate 1-D solution methods show some improvement for cases with low turbulence and a high rate-of-pressure-rise, where the wall function method tends to underpredict. However, the lack of complete experimental data does not permit the validation of these models.
Use of the models to examine changes in the predicted heat flux from changes in engine and initial conditions have shown that the initial turbulence kinetic energy and length scale have little affect on the heat flux, while the swirl velocity, swirl profile, compression ratio, and trapped mass all have a large influence on the magnitude of the heat flux.