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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.

The modern Diesel engine is one of the most versatile power sources available for mobile applications. The high fuel economy and torque of the Diesel engine has long resulted in global application for heavy-duty applications. Moreover, the high power and excellent driveability of today's turbo-charged small high-speed Diesel engines, coupled with their low CO2 emissions, has resulted in an increasing demand for Diesel powered light-duty vehicles. However, the demand for Diesel vehicles can only be realised if their exhaust emissions meet the increasingly stringent emissions legislation being introduced around the world. In the USA, both HDD and LDD vehicles are meeting strict emissions legislations since 2007 with the introduction of particle filters which will be further restricted from 2010 with the use of additional NOx contr5ol systems. In Europe, similar strict requirements are being implemented with Euro IV, Euro V and finally through Euro VI legislations.

A heavy duty US 2010/Euro VI type emission control 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 - excluded for this study). The advent of the US 2014 Green House Gas (GHG) rules has established a limit for tailpipe N2O emissions for on-road heavy duty Diesel engines, thus creating new challenges for catalyst design and system/engine calibration. In this paper, we discuss the effects of both catalyst system design and engine calibration on the formation of N2O across SCR catalysts. This study consisted of system testing on engine, modeling and component reactor testing. These three tools were used to evaluate how NO2 to NOx ratio and ammonia to NOx ratio (ANR) affect N2O formation. The study showed that all of the reviewed factors affect tailpipe N2O emissions.

The application of oxidation catalyst and particulate filter technology for the reduction of particulate matter (PM), hydrocarbons (HC) and carbon monoxide (CO) emissions from heavy duty diesel engines has become an established practice. The design and performance of such systems have been commercially proven to the point that the application of these technologies is cost effective and durable. The application of an effective NOx reduction technology in heavy duty diesel applications is more complicated since there are no passive NOx reduction technologies that can be fit onto HDD vehicles. However, Selective Catalytic Reduction (SCR) systems using Urea injection to achieve NOx reduction have become the technology of choice in Europe and have been applied to achieve Euro IV emissions levels on new HDD vehicles. In addition, retrofit SCR emission control systems have also been developed that can provide high NOx reduction when applied on existing HDD vehicles.

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.

Previous studies have shown that regenerating particulate filters are very effective at reducing particulate matter emissions from diesel engines. Some particulate filters are passive devices that can be installed in place of the muffler on both new and older model diesel engines. These passive devices could potentially be used to retrofit large numbers of trucks and buses already in service, to substantially reduce particulate matter emissions. Catalyst-type particulate filters must be used with diesel fuels having low sulfur content to avoid poisoning the catalyst. A project has been launched to evaluate a truck fleet retrofitted with two types of passive particulate filter systems and operating on diesel fuel having ultra-low sulfur content. The objective of this project is to evaluate new particulate filter and fuel technology in service, using a fleet of twenty Class 8 grocery store trucks. This paper summarizes the truck fleet start-up experience.