The goal of this research is to identify operating parameters that allow a diesel engine to use a typical gasoline three-way catalyst (TWC) as a primary NOx remover to meet upcoming stringent emission standards. Operating a diesel engine at the stoichiometric condition with a TWC can be a cost-effective solution since it uses proven technology compared to the adaptation of advanced combustion concepts, namely, low temperature combustion, or the use of selective catalytic reduction, as long as the fuel penalty associated with stoichiometric operation is manageable.
In the present study, firstly, the effects of intake pressure were scrutinized using two advanced concept nozzles, viz., group-hole nozzles (GHN) and two-spray angle nozzles (2SAN) in engine experiments. The engine experiments in the present study were performed with a 0.477-liter single-cylinder, high-speed direction-injection engine at 2000 rev/min and around 6 bar IMEP. The various intake pressure experiments confirmed that higher intake pressures and the correspondingly higher EGR rates exhibited lower fuel consumption. Then, the two advanced concept nozzles were employed to enhance mixture quality under low intake pressure, stoichiometric operation. The GHN exhibited approximately 40% lower soot and 2% lower fuel consumption with lean, non-stoichiometric, operation and 3% lower fuel consumption with no-EGR throttled stoichiometric operation. The 2SAN exhibited great improvement in terms of soot, particularly at relatively later injection timings, ?25? ? ?10? ATDC. In addition to the injector nozzles, further mixing enhancement by means of a longer ignition delay was achieved by utilizing the intake valve closing (IVC) timing delay. A 32-CA IVC timing delay was achieved with a 1-mm valve lift that retarded the start of combustion timing by 2 CA.
Finally, TWC performance experiments showed TWC achieved 98% NOx conversion efficiency with stoichiometric diesel exhaust. With 60?80% conversion efficiencies of hydrocarbon and carbon monoxide, TWC successfully lowered all three emission parameters below the US-2010 emission standard levels.