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A 4-way Heavy-Duty Diesel (HDD) emissions control aftertreatment system typically consists of diesel oxidation catalyst (DOC), catalyzed soot filter (CSF), urea-based selective catalytic NOx reduction (SCR) and NH₃ slip control catalyst (AMOX). Incorporating the SCR functionality into the soot filter (SCRoF) has great potential to reduce system costs and package volume/weight. In this paper, we discuss some of the recent Cu-Zeolite-based SCR on filter (SCRoF) developments targeting Passive filter regeneration applications. The on-engine investigation of complete DOC+SCRoF+AMOX system focused on three major areas: 1) SCR performance of NOx conversion efficiency and NH₃ slip under both steady state and transient testing conditions; 2) SCRoF system response to sulfur exposure and subsequent sulfur removal for activity recovery; and 3) Characteristics of filter soot load, pressure drop, and passive soot oxidation in SCRoF.

With the introduction of Euro III emission regulations for 2-wheelers in Europe, emission control for motorcycles and scooters has become a significant technological challenge. While many vehicles have shifted from 2-stroke to 4-stroke, they are mostly still open loop carbureted or in some cases fuel injected. Euro III regulation requires emission measurement from key-on and has a high speed phase for vehicles over 150cc engine displacement. The combination of cold start fuel enrichment (with or without secondary air injection) and high exhaust flow rates is particularly challenging for controlling the emissions of THC, CO and NOx simultaneously. If the engine is tuned lean to reduce THC and CO emissions, NOx emissions will increase during high speed operation. On the other hand, if the engines are rich tuned, this increases the cold start and/or high speed acceleration mode THC and CO emissions.

On-Board Diagnostics for emissions-related components require the monitoring of the catalytic converter performance. Currently, the dual Exhaust Gas Oxygen (EGO) sensor method is the only proven method for monitoring the catalyst performance for hydrocarbons (HC). The premise for using the dual oxygen sensor method is that a catalyst with good oxygen storage capacity (OSC) will perform better than a catalyst with lower OSC. A statistical relationship has been developed to correlate HC performance with changes in OSC. The current algorithms are susceptible to false illumination of the Malfunction Indication Light (MIL) due to: 1. The accuracy with which the diagnostic algorithm can predict a catalyst malfunction condition, and 2. The precision with which the algorithm can consistently predict a malfunction. A new algorithm has been developed that provides a significant improvement in correlation between the EGO sensor signals and hydrocarbon emissions.