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Diesel Particulate Filters (DPFs) are in common use in many applications for particulate matter (PM) control. Most examples of DPF usage follow a Diesel Oxidation Catalyst (DOC) providing NO2 for passive soot oxidation and fuel burning for active soot regeneration. The DPF is often catalyzed, (CDPF) to enhance passive regeneration by NO2, and to assist active regeneration by burning CO resulting from soot oxidation and any hydrocarbons passing through the DOC. Some applications with favorable NOx to PM ratios can operate without active regeneration, including applications with only CDPF for cost and packaging space savings. However, eliminating the DOC for applications that require both types of regeneration is difficult, as active regeneration must be accomplished by burning fuel within the CDPF, while adequately burning soot near the front.

There is growing interest in application of SCR on DPF (SDPF) for light and heavy duty applications, particularly to provide improvements in cold start emissions, as well as improvements in system cost and packaging [1, 2, 3]. The first of systems containing SDPF are just coming to market, with additional introductions expected, particularly for light duty and non-road applications [4]. To provide real world testing for a new SDPF product design prior to availability of OEM SDPF applications, an SDPF and one SCR catalyst were substituted in place of the original two SCR catalysts and a catalyzed diesel particulate filter (CDPF) on a Ford F250 HD pickup. To ensure that the on-road emissions would be comparable to the production system replaced, and to make sure that the control system would be able to operate without detecting some difference in behavior and seeing this as a fault, initial chassis dynamometer work was done before putting the vehicle on the road.

Non-road Tier 4 Final emissions standards offer opportunities for engines to be certified with DOC + SCR aftertreatment systems (ATS), where particulate matter (PM) emissions will be controlled by engine measures. These non-filter systems will not experience high thermal conditions common for filter regeneration and, therefore, will not have the secondary benefit of thermal events removing sulfur from the DOC and SCR aftertreatment. An experimental program was conducted on DOC + SCR systems in which the DOC was selected for the anticipated NO2 and sulfur management requirements of a fixed volume of 3 SCR types (vanadia, copper and iron). Each system was optimized to NOx conversion levels of 90%+ on NRTC cycles then exposed to accelerated sulfur poisoning and various cycles of increasing temperature after each poisoning to observe the performance recovery of the system. Specific sulfur management strategies are defined, depending on technology.