Abstract
The major long term challenge for the automotive industry is the substantial reduction of greenhouse gas emissions with a simultaneous reduction in all other regulated emissions. Although local pollutant emissions (specifically NOx, CO, HC and soot) are already being addressed through the use of aftertreatment systems and higher quality fuels, new emission standards that will be enforced in the next few years will be more stringent, especially on NOx and particulate matter (PM) emissions. The diesel particulate filter technology has been established as a favourable method and a necessity for the control of diesel PM emissions.
The ongoing research by the authors have aimed to develop a diesel emissions reduction system with enhanced performance by utilising hydrogen produced on-board in a exhaust gas assisted diesel fuel reformer. This type of fuel reforming process involves the on-board generation of hydrogen-containing gas by direct catalytic interaction of hydrocarbon fuels with engine exhaust gases.
The aim of this work is to design a fuel reformer-CRT-DPF system. The reformate (i.e. H2- rich gas) will be produced and introduced continuously into the DOC part of the CRT-DPF or directly to the catalyst coated DPF, when required (i.e. low load, low exhaust temperatures) in small concentrations (i.e. below 2000 ppm H2) in order to enhance NO to and NO2 oxidation. Initial results using a CRT DPF aftertreatment system showed the NO to NO2 oxidation over the DOC enhancing as the hydrogen addition was increased from 500 – 2000 ppm; however it was found to be dependent on the engine operation (i.e. use of EGR), exhaust gas conditions and composition. The increased NO2 concentration in the exhaust improved the soot oxidation at low temperatures and helped in maintaining a soot free DPF, as seen from the temperature changes and pressure drop trends along the filter.
Keywords: Diesel Oxidation Catalyst, NO2, Diesel Particulate Filter, Hydrogen