Low-Load Dual-Fuel Compression Ignition (CI) Engine Operation with an On-Board Reformer and a Diesel Oxidation Catalyst: Effects on Engine Performance and Emissions

Abstract

In the exhaust gas fuel-reforming method, part of the engine exhaust gas reacts with small amounts of engine fuel in a mini-reactor fitted in the exhaust gas recirculation (EGR) loop to produce gaseous fuel named reformed EGR (REGR). In this study, hot REGR (gas containing H2, CO, CH4, and CO2) was fed back to the engine inlet, so that the diesel engine in effect operated in dual fuel with inlet heating and EGR (CO2 existence). The effects of the diesel engine dual fueling with different REGR percentages on the engine performance and emissions have been examined. The study focused at low-load engine operation, where the conditions are not favorable for efficient gaseous fuel oxidation and engine combustion stability. The addition of the premixed gaseous fuel resulted in a remarkable reduction of both NOx and smoke engine emissions. Carbon monoxide and hydrogen oxidation efficiency can be improved by careful selection of REGR addition (e.g., premixed air/fuel ratio, inlet temperature, and reduced in-cylinder O2 concentration) and in-cylinder diesel injection timing. The use of Pt supported on Al2O3 as an oxidation catalyst at the engine exhaust can eliminate both CO and H2 at temperatures lower than the engine exhaust gas temperature at part loads. Preferably, in an actual engine reformer system, the uncombusted CO and H2 will be used to enhance the aftertreatment system (i.e., diesel particulate filter, NOx traps, and hydrocarbon-selective catalytic reduction of NOx) performance.