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For diesel exhaust aftertreatment applications with space limitations, as well as to move the selective catalytic reduction system (SCR) to a warmer location closer to the engine, DOC on CSF technology can be used. This technology combines the diesel oxidation catalyst (DOC) and catalyzed soot filter (CSF) functionalities in one component, thereby enabling volume reduction. DOC on CSF maintains the abatement of hydrocarbon (HC), carbon monoxide (CO), and particulate matter (PM), and the oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) for passive soot oxidation and fast SCR reaction of NOx on a downstream SCR catalyst. In this study, the performance of DOC on CSF was compared to a DOC + bare diesel particulate filter (DPF) and a DOC + CSF system, to understand the performance benefits and challenges. All the components were optimized individually for their respective functions. The DOC on CSF was optimized for NO oxidation and passive soot oxidation performance.

Sustained NOx reduction at low temperatures, especially in the 150-200 °C range, shares some similarities with the more commonly discussed cold-start challenge, however, poses a number of additional and distinct technical problems. In this project, we set a bold target of achieving and maintaining 90% NOx conversion at the SCR catalyst inlet temperature of 150 °C. This project is intended to push the boundaries of the existing technologies, while staying within the realm of realistic future practical implementation. In order to meet the resulting challenges at the levels of catalyst fundamentals, system components, and system integration, Cummins has partnered with the DOE, Johnson Matthey, and Pacific Northwest National Lab and initiated the Sustained Low-Temperature NOx Reduction program at the beginning of 2015 and completed in 2017.

Future light duty vehicles in the United States are required to be certified on the FTP-75 cycle to meet Tier 3 or LEV III emission standards [1, 2]. The cold phase of this cycle is heavily weighted and mitigation of emissions during this phase is crucial to meet the low tail pipe emission targets [3, 4]. In this work, a novel aftertreatment architecture and controls to improve Nitrogen Oxides (NOx) and Hydrocarbon (HC) or Non Methane Organic gases (NMOG) conversion efficiencies at low temperatures is proposed. This includes a passive NOx & HC adsorber, termed the diesel Cold Start Concept (dCSC™) catalyst, followed by a Selective Catalytic Reduction catalyst on Filter (SCRF®) and an under-floor Selective Catalytic Reduction catalyst (SCR). The system utilizes a gaseous ammonia delivery system capable of dosing at two locations to maximize NOx conversion and minimize parasitic ammonia oxidation and ammonia slip.

Future emissions regulations proposed for the Asian automotive industry (BS VI regulations for India and NS VI regulations for China) are strict and similar to EU VI regulations. As a result, they will require both advanced NOx control as well as advanced Particulate Matter (PM) control. This will drive implementation of full Catalyzed Diesel Particulate Filter (cDPF) and simultaneous NOx control using Selective Catalytic Reduction (SCR) technologies. In this work, we present the performance of various Diesel Oxidation Catalyst (DOC), cDPF, SCR and Ammonia slip catalyst (ASC) systems utilizing the World Harmonized Transient Cycle (WHTC). Aftertreatment Systems (ATS) required for both active and passive filter regeneration applications will be discussed. The sensitivity of key design parameters like catalyst technology, PGM loading, catalyst sizing to meet the regulation limits has been investigated.

The phase-in of US EPA Tier 3 and California LEV III emission standards require further reduction of tailpipe criteria pollutants from automobiles. At the same time, the mandate for reducing Green House Gas (GHG) emissions continuously lowers the exhaust temperature. Both regulations pose significant challenges to emission control catalyst technologies, especially for cold start emissions. The recently developed diesel cold start concept technology (dCSC™) shows promising results. It stores NOx and HC during the cold start period until the downstream catalytic components reach their operating temperatures, when the stored NOx/HC are subsequently released and converted. The technology also has oxidation functions built in and acts as a diesel oxidation catalyst under normal operating conditions. In a US DOE funded project, the diesel cold start concept technology enabled a high fuel efficiency vehicle to achieve emissions targets well below the SULEV30 emission standards.

Selective Catalytic Reduction (SCR) systems have been demonstrated as effective solutions for controlling NOx emissions from Heavy Duty diesel engines. Future HD diesel engines are being designed for higher engine out NOx to improve fuel economy, while discussions are in progress for tightening NOx emissions from HD engines post 2020. This will require increasingly higher NOx conversions across the emission control system and will challenge the current aftertreatment designs. Typical 2010/2013 Heavy Duty systems include a diesel oxidation catalyst (DOC) along with a catalyzed diesel particulate filter (CDPF) in addition to the SCR sub-assembly. For future aftertreatment designs, advanced technologies such as cold start concept (dCSC™) catalyst, SCR coated on filter (SCRF® hereafter referred to as SCR-DPF) and SCR coated on high porous flow through substrates can be utilized to achieve high NOx conversions, in combination with improved control strategies.

Selective Catalytic Reduction (SCR) catalysts have been demonstrated as an effective solution for controlling NOx emissions from diesel engines. Typical 2013 Heavy Duty Diesel emission control systems include a DOC upstream of a catalyzed soot filter (CSF) which is followed by urea injection and the SCR sub-assembly. There is a strong desire to further increase the NOx conversion capability of such systems, which would enable additional fuel economy savings by allowing engines to be calibrated to higher engine-out NOx levels. One potential approach is to replace the CSF with a diesel particulate filter coated with SCR catalysts (SCRF® technology, hereafter referred to as SCR-DPF) while keeping the flow-through SCR elements downstream, which essentially increases the SCR volume in the after-treatment assembly without affecting the overall packaging.

Selective Catalytic Reduction (SCR) catalysts have been demonstrated as an effective solution for controlling NOx emissions from diesel engines. There is a drive to reduce the overall packaging volume of the aftertreatment system for these applications. In addition, more active SCR catalysts will be needed as the applications become more challenging: e.g. lower temperatures and higher engine out NOx, for fuel consumption improvements. One approach to meet the challenges of reduced volume and/or higher NOx reduction is to increase the active site density of the SCR catalyst by coating higher amount of SCR catalyst on high porosity substrates (HPS). This approach could enable the reduction of the overall packaging volume while maintaining similar NOx conversion as compared to 2010/2013 systems, or improve the NOx reduction performance for equivalent volume and NH3 slip.

Stricter emission standards in the near future require not only a high conversion efficiency of the toxic air pollutants but also a substantial reduction of the greenhouse gases from automotive exhaust. Advanced engines with improved fuel efficiency can reduce the greenhouse gas emissions; their exhaust temperature is, however, also low. This consequently poses significant challenges to the emission control system demanding the catalysts to function at low temperatures both during the cold start period and under the normal engine operation conditions. In this paper, we will introduce a gasoline Cold Start Concept (gCSC™) technology developed for advanced stoichiometric-burn gasoline engines to meet future stringent emission regulations. To improve the low temperature performance of three-way catalysts, a novel Al2O3/CeO2/ZrO2 mixed oxide was developed.

Selective Catalytic Reduction (SCR) systems have been demonstrated as effective solutions for controlling NOx emissions from Heavy Duty diesel engines. Future HD diesel engines are being designed for higher engine out NOx to improve fuel economy, which will require increasingly higher NOx conversion to meet emission regulations. For future aftertreatment designs, advanced technologies such as SCR coated on filter (SCRF®) and SCR coated on high porous flow through substrates can be utilized to achieve high NOx conversion. In this work, different options were evaluated for achieving high NOx conversion. First, high performance NOx control catalysts were designed by using SCRF unit followed by additional SCR on high porosity substrates. Second, different control strategies were evaluated to understand the effect of reductant dosing strategy and thermal management on NOx conversion. Tests were carried out on a HD engine under transient test cycles.

Achieving early catalyst light-off is crucial if stringent emissions standards are to be met; if light-off is late, the emissions limit could be exceeded even before the catalyst starts to work. This paper presents a detailed simulation study of the factors affecting the light-off of a TWC. Simulation is not just faster and cheaper than vehicle testing, it also enables more insight into the factors affecting catalyst performance to be obtained. For example, changing the substrate (cell density and wall thickness) affects the rates of heat and mass transport, as well as the thermal mass of the catalyst. In a vehicle test, all three factors are changed at once, but with a simulation each of these factors can implemented one at time to enable the relative importance of these factors to be determined.

Catalytic emission control systems are installed on nearly all automobiles and heavy-duty trucks produced today to reduce exhaust emissions for the vehicles to meet government regulations. Current systems can achieve very high efficiencies in reducing tailpipe emissions once the catalytic components reach their operating temperatures. They are, however, relatively ineffective at temperatures below their operating temperature windows, especially during the cold start period of the vehicles. With the increasingly stringent government regulations, reducing the emissions during the cold start period before the catalytic components reach their operating temperatures is becoming a major challenge. For cold start HC control, HC traps based on zeolites have been investigated and commercialized for certain applications. For cold start NOx control, especially in lean burn engine exhaust, NOx storage and release catalysts have been evaluated.

Selective Catalytic Reduction (SCR) catalysts have been demonstrated as an effective solution for controlling NOx emissions from diesel engines. Typical 2010 Heavy-Duty systems include a DOC along with a catalyzed soot filter (CSF) in addition to the SCR sub-assembly. There is a strong desire to further increase the NOx conversion capability of such systems, to enable additional fuel economy savings by allowing engines to be calibrated to higher engine-out NOx levels. One potential approach is to replace the CSF with a diesel particulate filter coated with SCR catalysts (SCR-DPF) while keeping the flow-through SCR elements downstream, which essentially increases the SCR volume in the after-treatment assembly without affecting the overall packaging. In this work, a system consisting of SCR-DPF was evaluated in comparison to the DOC + CSF components from a commercial 2010 DOC + CSF + SCR system on an engine with the engine EGR on (standard engine-out NOx) and off (high engine-out NOx).

Oxidation of NO to NO₂ over a Diesel Oxidation Catalyst (DOC) plays an important role in different types of aftertreatment systems, by enhancing NOx storage on adsorber catalysts, improving the NOx reduction efficiency of SCR catalysts, and enabling the passive regeneration of Diesel Particulate Filters (DPF). The presence of hydrocarbon (HC) species in the exhaust is known to affect the NO oxidation performance over a DOC; however, specific details of this effect, including its underlying mechanism, remain poorly understood. Two major pathways are commonly considered to be responsible for the overall effect: NO oxidation inhibition, due to the presence of HC, and the consumption of the NO₂ produced by reaction with hydrocarbons. In this work we have attempted to decouple these two pathways, by adjusting the catalyst inlet concentrations of NO and NO₂ to the thermodynamic equilibrium levels and measuring the composition changes over the catalyst in the presence of HC species.

Since early 2010, most new medium- and heavy-duty diesel vehicles in the US rely on urea-based Selective Catalytic Reduction (SCR) technology for meeting the most stringent regulations on nitrogen oxides (NOx) emissions in the world today. Catalyst technologies of choice include Copper (Cu)- and Iron (Fe)-based SCR. In this work, the performances of Fe-SCR and Cu-SCR were investigated in the most commonly used DOC + CSF + SCR system configuration. Cu-SCR offered advantages over Fe-SCR in terms of low temperature conversion, NO₂:NOx ratio tolerance and NH₃ slip, while Fe-SCR demonstrated superior performance under optimized NO₂:NOx ratio and at higher temperatures. The Cu-SCR catalyst displayed less tolerance to sulfur (S) exposure. Reactor testing has shown that Cu-SCR catalysts deactivate at low temperature when poisoned by sulfur.

Emission control systems combining NOx Adsorber catalysts with Selective Catalytic Reduction catalysts (NAC + SCR) offer potential performance advantages for NOx control under lean conditions compared to systems consisting of only one of these technologies. The combined systems, however, also present new catalyst design challenges. In contrast to NAC-only systems, formation of NH₃ over the NAC component under NOx regeneration conditions is a desirable feature in the combined (NAC + SCR) system. The SCR component in the combined system needs to be as thermally durable as the stand-alone SCR technology and also has to withstand repeated high-temperature lean/rich transients encountered during periodic desulfation of the upstream NAC component. In this study, advanced NAC and SCR components were developed specifically for the combination system. The advanced NAC component exhibited a wider operating temperature window and higher NH₃ generation activity at reduced PGM loading.

Two major deactivation mechanisms of automotive catalysts during road usage are: 1. thermal aging 2. poison accumulation of oil-derived poisons such as zinc and phosphorus. A dynamometer-based aging cycle, incorporating a high-temperature low-poison mode to account for thermal aging followed by a low-temperature high-poison mode to account for poison accumulation, has been developed to allow the examination of catalyst formulations after exposure to both a harsh thermal and chemical aging environment. This type of aging cycle results in dynamometer-aged catalysts that are physically much more similar to road-aged catalysts than thermally-based dynamometer cycles. Using this aging-cycle, Pd-only, Pd-Rh and Pt-Rh light-off catalysts were examined. The Pd-Rh catalyst gave the best overall performance, with equivalent HC light-off performance to the Pd-only catalyst and equivalent NOx performance to the Pt-Rh catalyst.

Considerable work has been carried out to develop particulate control systems for light duty vehicles. These systems are required to operate under widely varying conditions of service. Examination of the extremes of operation shows the importance of the regeneration ability of the control system employed. In addition, a major requirement for a practical control system is minimum complexity. Discussed here is a catalyst system and the extension of the technology to allow for minimum complexity and the ability to operate at the defined extremes of use. The theory of the TRIM System and the results of evaluations on vehicles and test benches are given.

Public concern with city bus diesel emissions is worldwide. The operation of public transport in center city areas generates considerable localized pollution. This paper discusses the application of catalytic particulate control to various types of buses and gives details of the performance achieved in widely differing operating environments. On-road, in-service evaluations are reported and details given on the developments to arrive at the socially acceptable or “Friendly” bus.

Catalytic trap oxidizers developed for use in control of particulate emissions from diesel engines have been advanced to the vehicle installation stage. This paper discusses the development of complete vehicle systems. Methods and techniques of assisted regeneration are presented along with control system concepts. Installation of the trap unit as part of an integrated vehicle exhaust system is described, along with designs and results from various prototype builds.