Multidimensional Modeling of the Effects of Radiation and Soot Deposition in Heavy-duty Diesel Engines

A radiation model based on the Discrete Ordinates Method (DOM) was incorporated into the KIVA3v multidimensional code to study the effects of soot and radiation on diesel engine performance at high load. A thermophoretic soot deposition model was implemented to predict soot concentrations in the near-wall region, which was found to affect radiative heat flux levels. Realistic, non-uniform combustion chamber wall surface temperature distributions were predicted using a finite-element-based heat conduction model for the engine metal components that was coupled with KIVA3v in an iterative scheme. The more accurate combustion chamber wall temperatures enhanced the accuracy of both the radiation and soot deposition models as well as the convective heat transfer model. For a basline case, (1500 rev/min, 100% load) it was found that radiation can account for as much as 30% of the total wall heat loss and that soot deposition in each cycle is less than 3% of the total in-cylinder soot. The maximum in-cylinder radiation intensities were found to be highly localized. Small pockets of intense radiation lowered local temperatures in regions of high NO production, thus decreasing predicted NO levels significantly. However, the predicted engine-out soot levels were largely unaffected by radiation. The highest levels of wall heat flux, and correspondingly the highest wall temperatures, occurred in localized regions on the engine head and piston, usually in the vicinity of the fuel spray. Increased swirl was found to increase engine head temperatures since combustion gases were redirected toward the head. Computations at high load and boost showed that piston temperatures can exceed 700 K locally, thus, explaining the mechanism of piston damage seen under high load conditions.