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Ammonia oxidation (AMOX) catalysts are critical parts of most diesel aftertreatment systems around the world. These catalysts are positioned downstream of selective catalytic reduction (SCR) catalysts and remove unreacted NH3 that passes through the SCR catalyst. In many configurations, the AMOX catalyst is situated after a diesel oxidation catalyst and catalyzed diesel particulate filter that oxidize CO and hydrocarbons. However, in Euro V and proposed Tier 4 final aftertreatment architectures there is no upstream oxidation catalyst. In this study, the impact of hydrocarbons is evaluated on two different types of AMOX catalysts. One has dual washcoat layers-SCR washcoat on top of PGM washcoat-and the other has only a PGM washcoat layer. Results are presented for NH3 and hydrocarbon oxidation, NOx and N2O selectivity, and hydrocarbon storage. The AMOX findings are rationalized in terms of their impact on the individual oxidation and SCR functions.

Diesel particulate filters are designed to reduce the mass emissions of diesel particulate matter and have been proven to be effective in this respect. Not much is known, however, about their effects on other unregulated chemical species. This study utilized source dilution sampling techniques to evaluate the effects of a catalyzed diesel particulate filter on a wide spectrum of chemical emissions from a heavy-duty diesel engine. The species analyzed included both criteria and unregulated compounds such as particulate matter (PM), carbon monoxide (CO), hydrocarbons (HC), inorganic ions, trace metallic compounds, elemental and organic carbon (EC and OC), polycyclic aromatic hydrocarbons (PAHs), and other organic compounds. Results showed a significant reduction for the emissions of PM mass, CO, HC, metals, EC, OC, and PAHs.

A simple 1-dimensional filter model, with symmetric and asymmetric channels, has been developed to investigate the fundamental behavior and performance of ceramic partial diesel particulate filters (PFs). The governing equations of mass and momentum are similar to those of a full DPF [7, 15]. A standard DPF with the plugs at its inlet face removed has been referred to as a ‘rear-plugged PF’ while, one with the plugs at the outlet face removed has been referred to as a ‘front-plugged PF’ in the present study. Removal of some of the plugs from a standard ceramic DPF reduces the (i) overall pressure drop (ΔP) across the filter, (ii) filtration efficiency (FE) of the DPF, and (iii) manufacturing cost. Partial filters stand a high chance of being deployed in diesel exhaust after-treatment systems for the emerging markets (Brazil, Russia, India, China) that follow Euro 4 emission regulations.

An integrated system model containing sub-models for diesel engine, emissions, and aftertreatment devices has been developed. The objective is to study engine-device and device-device interactions. The emissions sub-models used are for NOx and PM (particulate matter) prediction. The aftertreatment sub-models used include a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF). Controllers have also been developed to allow for transient simulations, active DPF regeneration, and prevention/control of runaway DPF regenerations. The integrated system-level model has been used to simulate DPF regeneration via exhaust fuel injection ahead of the DOC. In addition, the controller model can use intake throttling to assist in active DPF regeneration if needed. Regeneration studies have been done for both steady engine load and with load transients. High to low engine load transients are of particular interest because they can lead to runaway DPF regeneration.

An experimental study was performed to investigate diesel particulate filter (DPF) performance during filtration with the use of real-time measurement equipment. Three operating conditions of a single-cylinder 2.3-liter D.I. heavy-duty diesel engine were selected to generate distinct types of diesel particulate matter (PM) in terms of chemical composition, concentration, and size distribution. Four substrates, with a range of geometric and physical parameters, were studied to observe the effect on filtration characteristics. Real-time filtration performance indicators such as pressure drop and filtration efficiency were investigated using real-time PM size distribution and a mass analyzer. Types of filtration efficiency included: mass-based, number-based, and fractional (based on particle diameter). In addition, time integrated measurements were taken with a Rupprecht & Patashnick Tapered Element Oscillating Microbalance (TEOM), Teflon and quartz filters.

Three distinct types of diesel particulate matter (PM) are generated in selected engine operating conditions of a single-cylinder heavy-duty diesel engine. The three types of PM are trapped using typical Cordierite diesel particulate filters (DPF) with different washcoat formulations and a commercial Silicon-Carbide DPF. Two systems, an external electric furnace and an in-situ burner, were used for regeneration. Furnace regeneration experiments allow the collected PM to be classified into two categories depending on oxidation mechanism: PM that is affected by the catalyst and PM that is oxidized by a purely thermal mechanism. The two PM categories prove to contribute differently to pressure drop and transient filtration efficiency during in-situ regeneration.

The effects of thermal and chemical aging on the performance of cordierite-based and high-porosity mullite-based diesel particulate filters (DPFs), were quantified, particularly their filtration efficiency, pressure drop, and regeneration capability. Both catalyzed and uncatalyzed core-size samples were tested in the lab using a diesel fuel burner and a chemical reactor. The diesel fuel burner generated carbonaceous particulate matter with a pre-specified particle-size distribution, which was loaded in the DPF cores. As the particulate loading evolved, measurements were made for the filtration efficiency and pressure drop across the filter using, respectively, a Scanning Mobility Particle Sizer (SMPS) and a pressure transducer. In a subsequent process and on a different bench system, the regeneration capability was tested by measuring the concentration of CO plus CO2 evolved during the controlled oxidation of the carbonaceous species previously deposited on the DPF samples.

Nitrogen dioxide (NO2) is known to pose a risk to human health and contributes to the formation of ground level ozone. In recognition of its human health implications, the American Conference of Governmental Industrial Hygienists (ACGIH) set a Threshold Limit Value (TLV) of 0.2 ppmv NO2 in 2012. For mobile sources, NO2 is regulated as a component of NOx (NO + NO2). In addition, the European Commission has indicated it is considering separate Euro 6 light-duty diesel and Euro VI heavy-duty diesel NO2 emissions limits likely to mitigate the formation of ground level ozone in urban areas. In this study, we conduct component-level reactor-based experiments to understand the effects that various aftertreatment catalyst technologies including diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR) catalyst and ammonia oxidation (AMOX) catalyst have on the formation and mitigation of NO2 emissions.

Fuel-borne catalysts (FBC) have demonstrated efficacy as an important strategy for integrated diesel emission control. The research summarized herein provides new methodologies for the characterization of engine-out speciated emissions. These analytical tools provide new insights on the mode of action and chemical forms of metal emissions arising from use of a platinum and cerium based commercial FBC, both with and without a catalyzed diesel particulate filter. Characterization efforts addressed metal solubility (water, methanol and dichloromethane) and particle size and charge of the target species in the water and solvent extracts. Platinum and cerium species were quantified using state-of-the-art high resolution plasma mass spectrometry. Liquid-chromatography-triple quad mass spectrometry techniques were developed to quantify potential parent Pt-FBC in the PM extracts. Speciation was examined for emissions from cold and warm engine cycles collected from an engine dynamometer.

With stringent emission regulations, aftertreatment systems with a Diesel Particulate Filter (DPF) and a Selective Catalytic Reduction (SCR) are required for diesel engines to meet PM and NOx emissions. The adoption of aftertreatment increases the back pressure on a typical diesel engine and makes engine calibration a complicated process, requiring thousands of steady state testing points to optimize engine performance. When configuring an engine to meet Tier IV final emission regulations in the USA or corresponding Stage IV emission regulations in Europe, this high back pressure dramatically impacts transient performance. The peak NOx, smoke and exhaust temperature during a diesel engine transient cycle, such as the Non-Road Transient Cycle (NRTC) defined by the US Environmental Protection Agency (EPA), will in turn affect the performance of the aftertreatment system and the tailpipe emissions level.

An integrated system model containing sub-models for a diesel engine, NOx and soot emissions, and a diesel particulate filter (DPF) has been used to simulate stead-state engine operating conditions. The simulation results have been used to investigate the effect of DPF loading and passive regeneration on engine performance and emissions. This work is the continuation of previous work done to create an overall diesel engine/exhaust system integrated model. As in the previous work, a diesel engine, exhaust system, engine soot emissions, and diesel particulate filter (DPF) sub-models have been integrated into an overall model using Matlab Simulink. For the current work new sub-models have been added for engine-out NOx emissions and an engine feedback controller. The integrated model is intended for use in simulating the interaction of the engine and exhaust aftertreatment components.

An overall diesel engine and aftertreatment system model has been created that integrates diesel engine, exhaust system, engine emissions, and diesel particulate filter (DPF) models using MATLAB Simulink. The 1-D engine and exhaust system models were developed using WAVE. The engine emissions model combines a phenomenological soot model with artificial neural networks to predict engine out soot emissions. Experimental data from a light-duty diesel engine was used to calibrate both the engine and engine emissions models. The DPF model predicts the behavior of a clean and particulate-loaded catalyzed wall-flow filter. Experimental data was used to validate this sub-model individually. Several model integration issues were identified and addressed. These included time-step selection, continuous vs. limited triggering of sub-models, and code structuring for simulation speed. Required time-steps for different sub models varied by orders of magnitude.

A procedure has been developed to build system level predictive models that incorporate physical laws as well as information derived from experimental data. In particular a soot model was developed, trained and tested using experimental data. It was seen that the model could fit available experimental data given sufficient training time. Future accuracy on data points not encountered during training was estimated and seen to be good. The approach relies on the physical phenomena predicted by an existing system level phenomenological soot model coupled with ‘weights’ which use experimental data to adjust the predicted physical sub-model parameters to fit the data. This approach has developed from attempts at incorporating physical phenomena into neural networks for predicting emissions. Model training uses neural network training concepts.

U.S. and European nonroad diesel emissions regulations have led to the implementation of various exhaust aftertreatment solutions. One approved configuration, a vanadium-based selective catalytic reduction catalyst followed by an ammonia oxidation catalyst (V-SCR + AMOX), does not require the use of a diesel oxidation catalyst (DOC) or diesel particulate filter (DPF). While certification testing has shown the V-SCR + AMOX system to be capable of meeting the nitrogen oxides, carbon monoxide, and particulate matter requirements, open questions remain regarding the efficacy of this aftertreatment for volatile and nonvolatile organic emissions removal, especially since the removal of this class of compounds is generally attributed to both the DOC and DPF.

More stringent emission requirements for nonroad diesel engines both in the U.S. and Europe have spurred the development of engines and exhaust aftertreatment technologies. In this study, one such system consisting of a diesel oxidation catalyst, zeolite-based selective catalytic reduction catalyst, and an ammonia oxidation catalyst was evaluated using both nonroad transient and steady-state cycles in order to understand the emission characteristics of this configuration. Criteria pollutants were analyzed and particular attention was given to organic compound and NO2 emissions since both of these could be significantly affected by the absence of a diesel particulate filter that typically helps reduce semi-volatile and particle-phase organics and consumes NO2 via passive soot oxidation. Results are then presented on a detailed speciation of organic emissions including alkanes, cycloalkanes, aromatics, polycyclic aromatic hydrocarbons and their derivatives, and hopanes and steranes.

Tailpipe particle number (PN) emission limits for heavy-duty diesel engines have been introduced as part of the off-highway Stage V standards. To meet the required limits a diesel particulate filter (DPF) with high filtration efficiency is required. The DPF relies on formation of a soot cake layer on the channel walls to achieve this high filtration efficiency. Off highway Stage V certification cycles are significantly higher in temperature than their on-highway counterparts, leading to difficulty in creating and maintaining a soot cake in the DPF. Hence for these applications meeting particle number requirements is challenging. To meet the high filtration efficiency requirements the DPF will have to reduce mean pore size, pore standard deviation, and increase wall thickness, in turn increasing backpressure, which results in a fuel consumption penalty. Another option is to evaluate the impact of temperature stable ash accumulation on DPF filtration efficiency.

Fuel properties impact the engine-out emission directly. For some geographic regions where diesel engines can meet emission regulations without aftertreatment, the change of fuel properties will lead to final tailpipe emission variation. Aftertreatment systems such as Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) are required for diesel engines to meet stringent regulations. These regulations include off-road Tier 4 Final emission regulations in the USA or the corresponding Stage IV emission regulations in Europe. As an engine with an aftertreatment system, the change of fuel properties will also affect the system conversion efficiency and regeneration cycle. Previous research works focus on prediction of engine-out emission, and many are based on chemical reactions. Due to the complex mixing, pyrolysis and reaction process in heterogeneous combustion, it is not cost-effective to find a general model to predict emission shifting due to fuel variation.

Advanced emission control systems for diesel engines usually include a combination of Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and Ammonia Slip Catalyst (ASC). The performance of these catalysts individually, and of the aftertreatment system overall, is negatively affected by the presence of oxides of sulfur, originating from fuel and lubricant. In this paper, we illustrated some key aspects of sulfur interactions with the most commonly used types of catalysts in advanced aftertreatment systems. In particular, DOC can oxidize SO2 to SO3, collectively referred to as SOx, and store these sulfur containing species. The key functions of a DOC, such as the ability to oxidize NO and HC, are degraded upon SOx poisoning. The impact of sulfur poisoning on the catalytic functions of a DPF is qualitatively similar to DOC.

Introduction of modern diesel aftertreatment, primarily selective catalytic reduction (SCR) designed to reduced NOx, has increased the presence of urea decomposition byproducts, mainly ammonia, in the aftertreatment system. This increase in ammonia has been shown to lead to particle formation in the aftertreatment system. In this study, a state of the art diesel exhaust fluid (DEF)-SCR system was investigated in order to determine the influence of DEF dosing on solid particle count. Post diesel particulate filter (DPF) particle count (> 23 nm) is shown to increase by over 400% during the World Harmonized Transient Cycle (WHTC) due to DEF dosing. This increase in tailpipe particle count warranted a detailed parametric study of DEF dosing parameters effect on tailpipe particle count. Global ammonia to NOx ratio, DEF droplet residence time, and SCR catalyst inlet temperature were found to be significant factors in post-DPF DEF based particle formation.