Search Results

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.

For diesel emission control technologies, reduction efficiencies of Particulate Matter (PM) control systems have been traditionally reported based on mass-based criteria. However, particle number-based criteria are now receiving increased attention. In this paper, results of real-time particle size distribution and number based evaluation of the effectiveness of multiple PM control technologies are reported on an HDD engine. An Engine Exhaust Particle Sizer (EEPS) was used for comparative analysis. The technologies that were evaluated included diesel oxidation catalysts (DOC), a DOC with an uncatalyzed wall-flow filter as a continuously regenerating diesel particulate filter (CR-DPF) system, a DOC with a catalytically coated wall-flow filter as a catalyzed CR-DPF (CCR-DPF), and a DOC with a partial filter as a continuously regenerating partial filter (CR-PF).

Diesel Particulate Filters (DPFs) such as the Continuously Regenerating Technology (CRT®) particulate filters are known to be highly effective in reducing PM emissions from diesel engines. Passive DPFs such as the CRT filter operate by collecting soot in the filter and subsequently oxidizing this soot in the presence of NO2 generated by an upstream Diesel Oxidation Catalyst (DOC). Both the NO2 generation and subsequent soot oxidation reactions require a certain minimum exhaust temperature. In addition, the engine out NOx to PM ratio is also critical for continuous and successful regeneration of the filter. However, these criteria may not always be met, particularly on low temperature applications such as refuse vehicles and newer low NOx (2.5 g/bhp-hr NOx) engines. This paper discusses the development of an actively regenerating diesel particulate filter (ACR-DPF) system for retrofit applications on heavy duty diesel vehicles.

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.

Diesel oxidation catalyst and particulate filter technologies are well established and their applications are well known. However, there are certain limitations with both technologies due to their inherent technical characteristics. Both technologies get 75-90% reduction of HC and CO. A typical oxidation catalyst can be applied to almost any heavy duty diesel application and achieve 20 to 30% reduction in PM mass but no significant reduction in the number of PM particles. On the other hand, diesel particulate filters are very effective at removing >90% of the particles by mass and >99% by number. Unfortunately, passive DPF technology cannot be applied to all applications since the filter regeneration is limited by engine out NOx to PM ratio as well as exhaust temperature. For this reason, particulate filters can not universally be applied to older “dirtier” engines with high PM emissions.

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.

The next generation advanced emission regulations have been proposed for the Indian heavy duty automotive industry for implementation from 2020. These BS VI emission regulations will require both advanced NOx control as well as advanced PM (Particulate Matter) control along with Particle Number limitations. This will require implementation of full DPF (Diesel Particulate Filter) and simultaneous NOx control using SCR technologies. DPF technologies have already been successfully implemented in Euro VI and US 10 HDD systems. These systems use low temperature NO2 based passive DPF regeneration as well as high temperature oxygen based active DPF regeneration. Effective DPF and DOC designs are essential to enable successful DPF regeneration (minimize soot loading in the DPF) while operating HDD vehicles under transient conditions. DOC designs are optimized to oxidize engine out NO into NO2, which helps with passive DPF regeneration.