Increasingly stringent emission regulations within the diesel engine industry, particularly with regard to particulate matter and oxides of nitrogen, have led to the development of a number of aftertreatment control technologies. Most of these control technologies address either oxides of nitrogen (NOx) emissions or particulate matter (PM) emissions, but not both. Until now no technologies were available that simultaneously reduced both these pollutants.Ceryx Incorporated has developed a novel four-way converter for the simultaneous reduction of PM, NOx, CO, and HC from diesel engines. The Ceryx systems integrate diesel particulate filters (DPF's) and lean NOx catalysts (LNC's) in the core of a proprietary heat exchanger. The heat exchanger serves to “recycle” heat from exothermic reactions over the catalyst by transferring heat from the hot exit gases to the cooler inlet gases. The regeneration performance of the DPF and the NOx reduction performance of the LNC are greatly enhanced by keeping them at an elevated temperature, particularly at light load conditions.Emissions and performance testing of the device placed on a modern 12-liter heavy-duty diesel and dual-fueled engine have demonstrated proof of concept. The results have demonstrated greater than 95% CO & HC oxidation, 90% particulate oxidation, and up to 46% NOx reduction. These results show that the device will enable a modern (circa 1996) engine to achieve the upcoming EPA 2004/2002 and Euro IV (2005) standards for heavy-duty engines without significant engine performance or fuel penalty. This paper details the principles of operation of the QuadCAT Four-Way Converter and reports the results of recent full-scale engine dynamometer tests.