The Effect of Semi-Circular Micro Riblets on the Deposition of Diesel Exhaust Particulate 2004-01-0969

Cooled EGR is recognized as a solution for the reduction of NOx in diesel exhaust gas. The key component of cooled EGR is a tubular type heat exchanger, however the performance drops because of particulate deposition whose characteristics and mechanism are not clrealy understood. Therefore the requirements for a EGR cooler is not only higher heat exchange performance and lower pressure loss, but also less performance deterioration due to DEP (Diesel Exhaust Particulate) deposition known as fouling. In order to improve heat transfer performance of an EGR cooler, it is considered that the surface with riblets aligned in the flow direction is preferable for the heat transfer surface because of its less skin friction and heat transfer enhancement. To apply riblet design to EGR coolers, however, it is necessary to investigate the performance with fouling from diesel particulate. In this report, first we clarified the characteristics of DEP deposition on smooth surfaces then we evaluated the diesel particulate deposition on a surface with semicircular scalloped riblets. We found that the deposition can be reduced by as much as 38% with proper riblet dimension (s⁺=10, h/s=0.5) compared to flat and smooth specimens. Observing with a stereoscopic microscope, for the DEP deposition reduction riblets, the DEP deposition film did not build up at the valley of the riblets.