Zirconia Based Ceramic, In-Cylinder Coatings and Aftertreatment Oxidation Catalysts for Reduction of Emissions from Heavy Duty Diesel Engines

Diesel engines are coming under stricter requirements to reduce emissions. particularly those of particulates and nitrogen oxides (NOx). Recently, the U. S. EPA put into place staged requirements for heavy duty diesel engines in urban bus applications which are aimed at ultimately bringing pre-1994 engines into particulate emissions compliance with 1994 heavy duty on-road truck standards (0. 1 g/bhp-hr TPM). This reflects the need to control emissions in crowded urban environments. Zirconia based ceramic combustion management coatings, although originally developed for adiabatic or low heat rejection engines to boost thermal efficiency, have also been shown to contribute to the reduction in diesel emissions. Heavy duty transient testing of rebuilt 2-stroke MUI diesel bus engines equipped with stabilized zirconia based coatings applied by thermal spray process have shown significant reduction in exhaust opacity relative to a baseline, uncoated engine. This was a reflection of the reduction in the dry carbon (soot) component of the particulate emissions. The combination of the zirconia in-cylinder coatings and an efficient diesel oxidation catalyst have allowed the 0.1 g/bhp-hr TPM standard to be met for rebuilt pre-1994 MY 2-stroke bus engine. Testing also showed that NOx emissions could also be reduced significantly via fuel injection timing retard without substantial increase in particulate emissions. Several years of field experience have been gained in diesel engines in urban bus applications equipped with in-cylinder zirconia based ceramic coatings and postmortem examination of coatings with over 100,000 miles service has shown very good durability.