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To enable better matching of Diesel Oxidation Catalyst (DOC) properties to aftertreatment system and application requirements, a systematic evaluation of the effects of sulfur poisoning and desulfation was undertaken on a number of Heavy Duty DOC formulations at representative Platinum Group Metal (PGM) loadings. Uniformly coated DOCs having PGM ratios from 1/0 Pt/Pd to 0/1 Pt/Pd with commercial HDD DOC washcoats were evaluated on a Tier 3 Non-Road engine. In addition, a new DOC formulation intended for reduced sulfur sensitivity, a DOC containing zeolite for hydrocarbon (HC) adsorption, and a layered DOC containing both high and low Pt/Pd ratio layers were compared. Two levels of PGM loading were included for three of the uniform sample formulations.

Investigations of on-road emissions performance of vehicles have been made using various methods and instrumentation, some of which are very complex and costly. For the particular case of NOx emissions on Diesel road vehicles equipped with SCR catalysts (Selective Catalytic Reduction), many of these vehicles are equipped with NOx sensor(s) for the purpose of OBD (On-Board Diagnostics), and the ECU (Engine Control Unit) makes this data available via the diagnostic connector under the SAEJ1979 protocol for light duty vehicles. Data for mass air flow and fuel flow are also available per J1979, so the ongoing NOx mass flow can be estimated when the NOx sensors are active with no additional instrumentation. Heavy duty pickup trucks with SCR systems from 3 major US manufacturers, each certified to the optional chassis certification of 0.2 g/mi NOx on the FTP75, were obtained to be evaluated for SCR system behavior under normal driving conditions.