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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.

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).

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.

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.

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Aftertreatment devices are exposed to exhaust poisons from fuel, oil and coolant. Studies on fuel- and lubricant-based poisoning have been widely published. However, diesel oxidation catalyst (DOC) and catalyzed soot filter (CSF) performance after exposure to constituents of coolant is not fully understood. Exhaust gas recirculation (EGR) cooler failure can cause a coolant leak into the exhaust that can reach the exhaust aftertreatment system. Coolant contains elements that can cause deterioration of aftertreatment components. This study focuses on the poisoning effect of coolant on the performance of a DOC + CSF system. The coolant introduction simulates an engine failure such as an EGR cooler internal fracture. DOC NO oxidation, quenching and hydrocarbon (HC) slip control performance during active regenerations are evaluated after slow and after consecutive fast coolant introduction and compared to the performance before the coolant exposure.

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.

This paper will review several different emission control systems for heavy duty diesel (HDD) applications aimed at future legislations. The focus will be on the (DOC+CSF+SCR+ASC) configuration. As of today, various SCR technologies are used on commercial vehicles around the globe. Moving beyond EuroVI/US10 emission levels, both fuel consumption savings and higher catalyst system efficiency are required. Therefore, significant system optimization has to be considered. Examples of this include: catalyst development, optimized thermal management, advanced urea dosing calibrations, and optimized SCR inlet NO:NO2 ratios. The aim of this paper is to provide a thorough system screening using a range of advanced SCR technologies, where the pros and cons from a system perspective will be discussed. Further optimization of selected systems will also be reviewed. The results suggest that current legislation requirements can be met for all SCR catalysts under investigation.

In recent years, ammonia slip catalysts (ASC) are being used downstream of an SCR system to minimize the ammonia slip. The dual-layer ASC is more attractive for its bi-functionality in reducing the ammonia and NOX emissions. It consists of two layers with the upper layer comprising a component with SCR functionality and the lower layer a PGM containing catalyst with oxidation functionality. Thus, both oxidation and SCR reactions take place in two different layers and are interlinked by the inter-layer mass transfer mechanism. In addition, adsorption and desorption kinetics between the gas and solid phases play a significant role. Mathematically, the overall system is a complex system of mass, momentum and energy transfer equations with temporal and spatial variables in both axial and radial directions. In this work, we focus on devising a suitable, computationally inexpensive model for such ASCs to be efficiently used for design, control and system optimization studies.

Parameter tuning was performed against data from a full scale engine rig with a Diesel Oxidation Catalysts (DOC). Several different catalyst configurations were used with varying Pt loading, washcoat thickness and volume. To illustrate the interplay between kinetics and mass transport, engine operating points were chosen with a wide variation in variables (inlet conditions) and both transient and stationary operation was used. A catalyst model was developed where the catalyst washcoat was discretized as tanks in series both radially and axially. Three different model configurations were used for parameter tuning, evaluating three different approaches to modeling of internal transport resistance. It was concluded that for a catalyst model with internal transport resistance the best fit could be achieved if some parameters affecting the internal mass transport were tuned in addition to the kinetic parameters.

The use of vanadia selective catalytic reduction (V-SCR) catalysts for NOX reduction from diesel engine exhaust is well known. These catalysts are also active for hydrocarbon (HC) and particulate matter (PM) oxidation. This dual functionality (oxidation and reduction) of V-SCR catalysts can help certain applications achieve the legislative limits with an improved margin. In this work, NOX reduction, HC and CO oxidation over V-SCR were studied independently and simultaneously in microreactor tests. The effect of various parameters (HC speciation, concentration, ANR, and NO₂/NOX ratio) was investigated and the data was used to develop a kinetic model. Oxidation of CO, C₃H₆, and n-C₁₀H₂₂ is first order in CO/HC, while C₇H₈ oxidation is less than first order in C₇H₈. All these reactions were zero order in O₂. Oxidation activity decreased in order: C₇H₈ ≻ n-C₁₀H₂₂ ≻ C₃H₆ ≻ CO. HC oxidation was inhibited by NH₃.

A combined experimental and modeling study was carried out to investigate the effects of Pt:Pd ratio on the performance of diesel oxidation catalysts (DOC) for heavy-duty applications1 (PGM<50 g/ft3). In the first part of this work, transient light-off and steady-state experiments were performed over a series of hydrothermally aged DOCs with different Pt:Pd ratios and PGM loadings. It was found that n-decane and NO oxidation activities increased monotonically as the Pt:Pd ratio was increased while the oxidation of unsaturated hydrocarbons (HC) (C3H6 and C7H8) first increased with an increase in Pt:Pd ratio and then plateaued at higher Pt content. In contrast, the CO oxidation exhibited opposite trend, with the catalyst containing low Pt (high Pd) level being more active. The presence of HC lowered the outlet NO2/NOx ratio by reducing the NO2 generated via NO oxidation back to NO. The negative effect of HCs on NO2/NOx ratio increased in the order: C3H6

This paper presents a two-part study on the effect of Pt:Pd ratio (at a constant total Pt+Pd loading of 120 g ft−3) on the catalytic performance of a Diesel Oxidation Catalyst (DOC) intended for light-duty applications, covering ratios across the full range from 100% Pd to 100% Pt. (Work on a heavy-duty DOC is presented in SAE 2015-01-1052). The first part of this paper presents a reactor study on the effect of Pt:Pd ratio on the catalytic activity of key reactions occurring individually over the DOC, including the oxidation of CO, C3H6, n-C10H22, CH4 and NO. For some reactions, activity increases continuously with Pt content (oxidation of n-C10H22 and NO); in contrast the activity for CH4 oxidation increases with decreasing Pt content (increasing Pd content), while CO and C3H6 oxidation exhibit more complicated dependencies. The second part presents the development of a one-dimensional model capable of predicting the effect of Pt:Pd ratio on DOC performance.