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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.

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.

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.

Significant reduction in Nitrogen Oxide (NOx) emissions will be required to meet LEV III/Tier III Emissions Standards for Light Duty Diesel (LDD) passenger vehicles. As such, Original Equipment Manufacturers (OEMs) are exploring all possible aftertreatment options to find the best balance between performance, durability and cost. The primary technology adopted by OEMs in North America to achieve low NOx levels is Selective Catalytic Reduction (SCR). The critical parameters needed for SCR to work properly are: an appropriate reductant such as ammonia (NH3) provided as Diesel Exhaust Fluid (DEF), which is an aqueous urea solution 32.5% concentration in weight with water (CO(NH2)2 + H2O), optimum operating temperatures, and optimum nitrogen dioxide (NO2) to NOx ratios (NO2/NOx). The NO2/NOx ratio is most influenced by Precious Group Metals (PGM) containing catalysts upstream of the SCR catalyst.

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.

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.

The nonroad Final Tier 4 US EPA emission standards require 88% reduction in NOx emission from the Interim Tier 4 standards. It is necessary to utilize aftertreatment technologies to achieve the required NOx reduction. The development of a fuel reformer, lean NOx trap (LNT) and optional selective catalytic reactor (SCR) on a John Deere 4045 nonroad engine is described in this paper. The paper discusses aftertreatment system performance, catalyst formulations and system controls of a fuel vaporizer, fuel reformer, LNT and SCR system designed to meet the nonroad Final Tier 4 emission standards. The 4045 John Deere engine was calibrated and integrated with the aftertreatment system. The system performance was characterized in an engine dynamometer performance test cell, durability test cell and on a vehicle. The catalyst performance was evaluated using aged catalysts and a detailed description of the LNT, DPF and SCR catalysts is provided.

In order to allow continued production of the AM General Optimizer 6500 during MY 2007 through 2010 this IDI engine (Indirect Injection - swirl chamber) requires sophisticated aftertreatment controls while maintaining its fuel economy and durability. The main purpose of the development program was to retain the relatively inexpensive and simple base engine with distributor pump and waste-gated turbocharger, while adding hardware and software components that allow achievement of the phase-in emission standards for 2007 through 2010. The aftertreatment system consists of Diesel Oxidation Catalyst (DOC), NOx Adsorber Catalyst (or DeNOx Trap - DNT) and Diesel Particle Filter (DPF). In addition to the base hardware, an intake air throttle valve and an in-exhaust fuel injector were installed. The presented work will document the development process for a 2004 certified 6.5 l IDI heavy-duty diesel engine to comply with the 2007 heavy-duty emission standards.