Characterization of heat-up diesel oxidation catalysts through gas flow reactor and in-situ engine testing

Abstract

This study characterizes the performance of several diesel oxidation catalyst (DOC) formulations with respect to their ability to heat up engine exhaust for the purpose of regenerating a diesel particulate filter or desulphating a lean nitrogen oxide (NO x) trap. Platinum (Pt), platinum—palladium (Pt—Pd), and platinum—palladium+cerium oxide (Pt—Pd+CeO2) are characterized using gas flow reactor experiments and in-situ engine tests. The feed gas from conventional diesel combustion and the feed gas from low-temperature premixed charge compression ignition (PCI) combustion are compared. An in-cylinder post-injection strategy is used to add the chemical energy needed to support DOC exothermic reactions, and the effect of post-injection timing is studied. The effects of carbon monoxide (CO), hydrocarbon (HC), and oxygen (O2) partial pressures on light-off characteristics are also investigated. Reactor tests show that Pt—Pd exhibits the lowest light-off temperature, followed by Pt—Pd+CeO2 and then Pt, regardless of mixture composition and O2 concentration. In-situ engine tests demonstrate that PCI is superior to conventional combustion in increasing the exhaust gas temperature at the same post-fuel-injection quantity, but only if the exhaust gas temperature is high enough to oxidize HCs and CO in lieu of sufficient O2. However, PCI produces significant particulate matter (PM) as post-injection timing is retarded. To avoid an increase in PM emission, an alternative method to introduce fuel should be considered.