Controlling diesel NOx & PM emissions using fuel components and enhanced aftertreatment techniques: developing the next generation emission control system

Abstract

The following research thesis focuses on methods of controlling nitrogen oxides (NO\(_X\)) and particulate matter (PM) emissions emitted from a low temperature diesel exhaust. This involves studying the influence of hydrogen (H\(_2)\) on various aftertreatment devices such as hydrocarbon selective catalytic reduction (HC-SCR) over silver-alumina (Ag-Al\(_2\)O\(_3\)) catalysts for lean NO\(_X\) reduction, platinum diesel oxidation catalysts (DOC) for nitrogen dioxide (NO\(_2)\) production and passive regeneration methods for the diesel particulate filter (DPF). H2 was implemented on-board either through diesel exhaust gas fuel reforming or via the simulation of ammonia (NH\(_3\)) dissociation. Both methods showed to be very effective in enhancing the activity of a silver HC-SCR catalyst for the reduction of NO\(_X\) with conversions reaching 90% with the aid of an upstream DPF. A combined DOC and catalysed DPF (cDPF) configuration proved promising for passive regeneration in the presence of reformed exhaust gas recirculation (REGR). The addition of H\(_2\) over the DOC led to an improved catalyst light-off temperature and increased rate of oxidation for NO\(_2\) production. Implementing filtered EGR (FEGR) removes the hydrocarbon (HC) and soot recirculation penalty, thus minimising particulate growth which results in a significantly reduced engine-out soot emission during exhaust gas recirculation (EGR) and hence, an improved NO\(_X\)/soot ratio. Introducing fuel components which enhance the cetane number and oxygenate the diesel fuel allow better control of the NO\(_X\)/soot trade-off with improved soot oxidation properties.