Development of an Automated Testbench for Functional Testing of Dosing Unit

<div class="section abstract"><div class="htmlview paragraph">Diesel aftertreatment (AT) systems are critical for controlling emissions of CO, HC, NO<sub>X</sub>, and PM in the on-road transportation sector. Ensuring compliance with regulatory standards throughout the AT system's lifespan requires precise prediction of various degradation mechanisms under real-world operating conditions and mitigating their impact through proper catalyst sizing and advanced controls. In the SwRI A2CAT-II consortium, a medium-duty diesel engine production aftertreatment system was subjected to full useful life aging, involving chemical poisoning with phosphorus (P) and sulfur (S) species, along with hydrothermal aging following the DAAAC protocol. This study was aimed to model and predict the aging trajectory of this production AT system thereby capturing changes in system dynamics under both steady-state and transient conditions. The system, designed to meet the 0.2 g/bhp-hr standard, comprised a Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and Ammonia Slip Catalyst (ASC). It was aged to 3600 hours equivalent to the DAAAC protocol and tested across a series of steady-state and regulatory cycles (HFTP, RMC, and LLC) at degreened, 33%, 66%, and 100% aging points. A linear decrease in system NOx conversion was observed between 0% to 66% aging, followed by a nonlinear drop from 66% to 100%. The cumulative decline in NOx conversion was 0.8%, which could significantly impact systems designed to meet a 0.05 g/bhp-hr target.</div><div class="htmlview paragraph">IntroductionAftertreatment durability demonstration is a mandatory validation exercise for on-road medium and heavy-duty diesel engine certification. This requirement ensures that the emission compliance can be achieved for the intended full useful life (FUL) of the engine system or multiple vehicle families. Conventional Deterioration Factor (DF) approach considers linear effect of sulfur and phosphorous poisoning on the catalysts over the entire useful life based on performance from 33% of aging the catalysts and extrapolating them to FUL. However, based on various studies, the impact of fuel derived Sulfur on diesel aftertreatment components was found to be exponentially significant particularly on the SCR due to the sulfur poisoning effect which require an active means to liberate sulfur to maintain appropriate SCR NOx conversion performance. Phosphorous from lubricating oil is known to adversely affect the activity of the oxidation catalyst in a catalyzed DPF thereby reducing the passive regenerative performance of DPF. For these reasons, an extensive understanding of chemical poisoning (particularly Sulfur and Phosphoros) and hydrothermal aging are warranted to design, validate and demonstrate the durability of aftertreatment components that are subjected to the prolonged chemical exposure.</div><div class="htmlview paragraph">To address the extensive challenges in durability demonstration, the Diesel Aftertreatment Accelerated Aging Protocol, or DAAAC, was developed by Southwest Research Institute as a part of consortium effort that includes input from diesel engine manufacturers [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span>]. DAAAC is an accelerated aging cycle developed for each application based on the available field data. It includes the exposure from hydrothermal aging, sulfur and lubricant derived poison at accelerated rates. The protocol also requires the entire aftertreatment system to be aged as a complete system, since the upstream components, such as DOC, can impact the chemical makeup of sulfur derived constituents.</div><div class="htmlview paragraph">The protocol does not introduce chemical constituents not normally observed in the field. The accelerated chemical exposure rate is limited only to a degree that has previously demonstrated successful correlation to normal, unaccelerated aging. The Protocol also requires that chemical aging mechanisms are to be introduced and / or consumed in a manner representative of the engine’s defined consumption pathways. Examples include sulfur exposure via high sulfur fuel or gaseous SO<sub>2</sub> and oil consumption via pre-combustion / post-combustion pathways. The Protocol also does not introduce chemical components that are not normally present in oil or fuel (other than doping the fuel with higher concentrations of sulfur, but this amount is relatively small). A comprehensive step by step breakdown of DAAAC protocol is presented elsewhere [<span class="xref">2</span>].</div><div class="htmlview paragraph">The primary objective of this paper is to disseminate the observation of long-term impacts of chemical poisoning and hydrothermal aging on a production aftertreatment catalyst subjected to FUL DAAAC protocol. The results of this experimental campaign were used to develop and validate a model capable of predicting hydrothermal and chemical aging mechanisms of conventional diesel aftertreatment to optimize long term emissions reduction performance. The paper is divided into following sections: <ol class="list nostyle"><li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Introduction: An overview of the system</div></li><li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">Background: A review of literature in the field of diesel AT aging</div></li><li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">Test Campaign: Description of experimental setup used for collection of both steady state and transient data.</div></li><li class="list-item"><span class="li-label">4</span><div class="htmlview paragraph">Experimental setup: Description of burner stand used for data collection.</div></li><li class="list-item"><span class="li-label">5</span><div class="htmlview paragraph">Results and Discussion: Description of experimental results followed by discussion about underlying degradation mechanism identified through simulation work.</div></li><li class="list-item"><span class="li-label">6</span><div class="htmlview paragraph">Summary and conclusion</div></li></ol></div></div>

<div class="htmlview paragraph">The tightening legislation in the on-road heavy-duty diesel area means that pollution control systems will soon be widely introduced on such engines. A number of different aftertreatment systems are currently being considered to meet the incoming legislation, including Diesel Particulate Filters (DPF), Diesel Oxidation Catalysts (DOC) and Selective Catalytic Reduction (SCR) systems.</div> <div class="htmlview paragraph">Relatively little is known about the interactions between lubricant-derived species and such aftertreatment systems. This paper describes the results of an experimental program carried out to investigate these interactions within DPF, DOC and SCR systems on a state-of-the-art 9 litre engine.</div> <div class="htmlview paragraph">The influence of lubricant composition and lube oil ash level was investigated on the different catalyst systems. In order to reduce costs and to speed up testing, test oil was dosed into the fuel. Tests without dosing lubricant into the fuel were also run.</div> <div class="htmlview paragraph">Driving distances of up to 115,000 km (based on oil consumption) were simulated in these experiments. Following such treatments, no significant change in the activity of the CR-DPF oxidation catalyst, Diesel Oxidation Catalysts or SCR catalysts were observed. In each case, the distribution of oil-derived species was studied as a function of distance down the catalyst. It was found that the Ca, Zn and P were generally present in higher concentrations at the front of the catalyst, decreasing down the unit. In contrast, sulfur is distributed evenly throughout the length of each catalyst. This is because sulfur can be deposited from the gas phase and is more mobile on the catalyst surface.</div> <div class="htmlview paragraph">Interestingly, when doping high ash oil into the fuel it was found that the back pressure of the DPF system increased rapidly. This is particularly important since it is known that used engine oil is sometimes poured back into the fuel tank for disposal. These results imply that this practice may strongly affect the efficiency of DPF devices.</div> <div class="htmlview paragraph">This rapid increase in back pressure is a consequence of doping the fuel with the high ash oil, since operation of the engine with the high ash oil without doping, or with a low ash oil with doping, resulted in only a gradual increase in back pressure. In addition, the distribution of the ash in the filter was strongly affected when doping the high ash oil into the fuel, in that the ash was uniformly distributed down the length of the filter. In the other experiments carried out here, and in measurements of field-aged filters, the ash thickness increases with distance into the filter. These observations reveal that care needs to be taken when doping oil into the fuel to accelerate the observation of oil-derived effects in DPF systems.</div>

<div class="section abstract"><div class="htmlview paragraph">Over the past few years, drastic steps have been taken to regularize emission norms for various segments in India. One of the major reforms done was separating construction equipment and agricultural vehicles to differentiate and define regulations effectively. Transition Emission Measure TREM IV emission norms have been implemented in India, and TREM V will also be launched soon. These changes to emission norms have increased the need for the implementation of after-treatment systems (ATS) in off-highway vehicle applications. Earlier, these systems were widely used for on highway vehicles. These emission norms target hydrocarbons, particulate matter, nitrogen oxide and carbon monoxide. Due to which, the demand for diesel oxidation catalysts (DOC) and diesel particulate filters (DPF) has increased in construction equipment and agricultural vehicles.</div><div class="htmlview paragraph">Although ATS has been in use for a long time, there are certain challenges associated with its integration into vehicles. As the space available on the vehicle is limited and there are high-temperature neighboring components, this can impact performance and increase safety-related risks for the end user. This study focuses on the integration challenges of ATS in tractor applications. Due to the limited available space, ATS must be integrated under the bonnet of vehicles for some applications. During static regeneration, the high temperature from the ATS heats up the bonnet and can pose a safety risk to the end user operating the vehicle. Some of the best practices to control heat rise from ATS have been discussed in this paper.</div><div class="htmlview paragraph">To understand the heat transfer in the actual application around ATS, a comprehensive repeatable test was done on the actual vehicle to collect critical information during various operating cycles of the vehicle. Air velocity was also measured during vehicle operation to understand the impact of forced convection on ATS. Validation of the actual test with steady state CFD simulation helped understand heat transfer on ATS. Validated CFD thermal model helps in comparing various design changes and identify thermal risks during high temperature conditions. A close correlation between the test and CFD simulation also helped in understanding the risk of high temperatures on the bonnet of vehicles. The modeling approach, test setup details, and critical factors affecting the performance of ATS have been discussed in detail in this study.</div></div>

<div class="htmlview paragraph">Selective Catalytic Reduction (SCR) is the dominant solution for meeting future NO<sub>x</sub> reduction regulations for heavy-duty diesel powertrains. SCR systems benefit from closed-loop control if an appropriate exhaust gas sensor were available. An ammonia sensor has recently been developed for use as a feedback element in closed-loop control of urea dosing in a diesel SCR aftertreatment system. Closed-loop control of SCR dosing enables the SCR system to be robust against disturbances and to meet conformity of production (COP) and in-use compliance norms.</div> <div class="htmlview paragraph">The ammonia sensor is based on a non-equilibrium electrochemical principle and outputs emf signals. The sensor performs well when tested in a diesel engine exhaust environment and has minimum cross interference with CO, HC, NO, NO<sub>2</sub>, SO<sub>2</sub>, H<sub>2</sub>O and O<sub>2</sub>.</div> <div class="htmlview paragraph">Previous work, done in a simulation environment, demonstrated that an ammonia sensor provides the optimal feedback for urea dosing control algorithms in closed-loop SCR systems. A model-based SCR control strategy deploying an ammonia feedback sensor demonstrated high NO<sub>x</sub> conversion, low NH<sub>3</sub> slip and good robustness against disturbances. In this paper, FTP, ETC and ESC test data will be presented confirming these results. NO<sub>x</sub> conversions as high as 91% are measured in combination with 30% urea injection error and a 25 ppm NH<sub>3</sub> slip constraint. Test results using the Delphi ammonia sensor for control are compared with test results utilizing a commercially available NO<sub>x</sub> sensor for control.</div>

<div class="section abstract"><div class="htmlview paragraph">Increasing concerns due to global warming have led to stringent regulation of greenhouse gas (GHG) emissions from diesel engines. Specifically, for GHG phase-2 regulation (2027), more than 4% improvement is needed when compared to phase-1 regulation (2017) in the light heavy-duty (LHD) diesel engine category. At the same time, California Air Resources Board (CARB) and Environmental Protection Agency (EPA) have proposed the new Low NOx standards that require up to 90% reduction in tailpipe (TP) NOx emissions in comparison to the current TP NOx standards that were implemented in 2010. In addition, CARB and EPA have proposed new certification requirements – Low Load Cycle (LLC) and revised heavy-duty in-use testing (HDIUT) based on the moving average window (MAW) method that would require rigorous thermal management. Hence, strategies for simultaneous reduction in GHG and TP NOx emissions are required to meet future regulations.</div><div class="htmlview paragraph">This paper presents potential pathways to achieve the GHG phase-2 and the ultra-low NOx (ULN) regulations with minimum changes in engine design, while meeting the constraints that need to be considered for engine performance stability, component durability, and vehicle drivability. Experimental evaluations were performed focusing on transient cycles such as heavy-duty Federal Test Procedure (hereafter referred as FTP), LLC, and custom transient cycles for HDIUT assessment. We used a model-year (MY) 2021 production Isuzu diesel engine and an advanced dual-dosing aftertreatment system comprising of a close-coupled SCR (ccSCR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR), and Ammonia Slip Catalyst (ASC). Conventional thermal management techniques such as multi-injection, intake, and exhaust throttling were implemented to achieve the emissions targets. In addition to the proposed system design, this paper presents following test results from a full-scale system evaluation: <ol class="list nostyle"><li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Achieve rapid and sustained turbine-out exhaust temperatures (>200°C) while meeting the engine-out emissions constraints for soot and total hydrocarbon (THC) emissions.</div></li><li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">A summary of TP NOx, TP N2O and GHG emissions over a composite FTP and LLC.</div></li><li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">HDIUT assessment results and observations for LLC and custom transient cycles.</div></li><li class="list-item"><span class="li-label">4</span><div class="htmlview paragraph">Robustness evaluation of TP NOx emissions for composite HDT, LLC and custom transient cycles by imposing component variations.</div></li></ol></div></div>

<div class="section abstract"><div class="htmlview paragraph">Engine and aftertreatment solutions have been identified to meet the upcoming ultra-low NO<sub>x</sub> regulations on heavy duty vehicles in the United States. These standards will require changes to current conventional aftertreatment systems for dealing with low exhaust temperature scenarios while increasing the useful life of the engine and aftertreatment system. Previous studies have shown feasibility of meeting the US EPA and California Air Resource Board (CARB) requirements. This work includes a 15L diesel engine equipped with cylinder deactivation (CDA) and an aftertreatment system that was fully DAAAC aged to 800,000 miles. The aftertreatment system includes an e-heater (electric heater), light-off Selective Catalytic Reduction (LO-SCR) followed by a primary aftertreatment system containing a DPF and SCR. The e-heater was capable of providing up to 10 kW, however for the purpose of this project, lower power settings of 2.5 kW and 5 kW were studied in combination with CDA for lowest possible CO2 emissions. Test cycles included the heavy duty FPT (hot and cold), a low load cycle, a beverage cycle, and a stay hot operation. The data found in this study show how the application of a low power e-heater enables an engine with CDA and an aftertreatment system after 800,000 miles aging to meet ultra-low NO<sub>x</sub> emissions with minimum CO<sub>2</sub> penalty.</div></div>

<div class="htmlview paragraph">Diesel engine exhaust has been an area of research since the early 80's because of their harmful nature. The upcoming EPA regulations require substantial reductions in NO<sub>x</sub> and Particulate Matter (PM) and an aftertreatment system will likely be needed to meet these regulatory emissions levels. A more advanced technology in Aftertreatment system uses in-line fuel reformer to convert injected diesel fuel to hydrogen-rich reformates. It is used as the rich component for regenerating the Lean NO<sub>x</sub> Trap (LNT). The LNT regeneration process produces ammonia (NH3) that enables further NO<sub>x</sub> reduction in a downstream Selective Catalytic Reduction (SCR). A Diesel Particulate Filter (DPF) provides PM reduction capability in the system. The high conversion efficiency of regeneration cycle demands complete vaporization and uniform distribution of the injected fuel. Computational Fluid Dynamics simulation is effective in optimizing geometrical parameters to achieve the above requirements.</div> <div class="htmlview paragraph">This paper discusses simulations carried out to guide the experimental setup, compare fuel injection systems and to optimize the location and the orientation of mixing elements. The results obtained were qualitatively validated with test data. An innovative technique has been implemented in FLUENT 6.3 to model the spray formation to overcome the detailed modeling of the injector. This technique takes input from experimental spray distribution data. The system parameters such as mixing elements, dozer location, fluid properties and dozer types were optimized. However, in order to reduce the dependency on the experiment, separate study is also carried out to simulate the injection phenomena that include internal flow of the injector and spray characteristic as well. This simulation manifests the underlying complex spray physics and predicts the spray parameters. The methodology that has been developed during these studies can be leveraged for investigation of droplet distribution, mixing flow and phase transformation</div>

<div class="section abstract"><div class="htmlview paragraph">Aftertreatment durability demonstration is a required validation exercise for on-road medium and heavy-duty diesel engine certification. The demonstration is meant to validate emissions compliance for the engine and aftertreatment system at full useful life or FUL. Current certification practices allow engine manufacturers to complete partial aging and then extrapolate emissions performance results to FUL. While this process reduces the amount of service accumulation time, it does not consider changes in the aftertreatment deterioration rate. Rather, deterioration is assumed to occur at a linear rate, which may lead to false conclusions relating to emissions compliance.</div><div class="htmlview paragraph">With CARB and EPA’s commitment to the reduction of criteria emissions, emphasis has also been placed on revising the existing certification practices. The updated practices would require engine manufacturers to certify with an aftertreatment system aged to FUL. By utilizing an application-specific field cycle, this approach could, theoretically, generate FUL field representative parts. Thus, the requirement would validate field emissions compliance with higher certainty. Establishing a more stringent certification requirement also brings challenges to engine manufacturers. For example, a heavy-duty on-road application would require 9,800 hours of service accumulation time or 14 months. This time commitment poses several issues for engine manufacturers, which include reduced development cycle scheduling and an increased cost burden.</div><div class="htmlview paragraph">To address manufacturer challenges, regulators are proposing accelerated aging as an acceptable alternative to conventional aging. The Diesel Aftertreatment Accelerated Aging Cycle protocol, or DAAAC, is an accelerated aging methodology that considers primary catalyst deterioration mechanisms. This includes exposure to hydrothermal aging, sulfur, and lubricant-derived poisons at accelerated rates. The methodology utilizes application-specific information to derive the aging cycle modes and deterioration mechanism exposure rates. The following work will consider tailpipe emission results from a conventionally aged aftertreatment system and two accelerated aged systems utilizing the DAAAC protocol. The objective of the work was to validate the DAAAC approach on two accelerated aging platforms. The results will consider the performance deterioration utilizing certification cycles like the HD-FTP and RMC.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Hybridization is a promising way to further reduce the CO<sub>2</sub> emissions of passenger vehicles. However, high engine efficiencies and the reduction of engine load, due to torque assists by an electric motor, cause a decrease of exhaust gas temperature levels. This leads to an increased time to catalyst light-off, resulting in an overall lower efficiency of the exhaust aftertreatment system (ATS). Especially in low load driving conditions, at cold ambient temperatures and on short distance drives, the tailpipe pollutant emissions are severely impacted by these low ATS efficiency levels.</div><div class="htmlview paragraph">To ensure lowest emissions under all driving conditions, catalyst heating methods must be used. In conventional vehicles, internal combustion engine measures (e.g. usage of a dedicated combustion mode for late combustion) can be applied. A hybrid system with an electrically heated catalyst (EHC) enables further methods such as the increase of engine load by the electric motor or electric catalyst heating. Since these methods result either directly or indirectly in additional fuel consumption there is a conflict of objectives between a fast catalyst heat-up and the reduction of fuel consumption.</div><div class="htmlview paragraph">This trade-off is addressed by an energy and emission management, which controls the split of the propulsion power between the combustion engine and electric motor, the electric catalyst heating and the selection of the combustion mode. Such a management system, based on offline-optimized rules, is presented in this paper. The results for different driving cycles are compared to those from a conventional non-hybrid vehicle in a detailed simulation framework, for a 48V P0 Diesel hybrid including an exhaust aftertreatment system with EHC. With the help of the EHC the NO<sub>x</sub> level was reduced significantly especially during city and short distance drives. On the WLTC a CO<sub>2</sub> saving of 7 % was achieved, maintaining the same NO<sub>x</sub> emissions level.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Achieving zero emissions across transportation is a tremendous challenge. The upcoming Euro 7/VII standards, set to be enforced in 2025, will mandate further reduction in ICEs exhaust emissions. Thus, additional improvements and potential new technologies and fuels are needed to design ultra-low emissions vehicles.</div><div class="htmlview paragraph">Hydrogen seems to be a very attractive fuel, thanks to its high lower heating value, clean combustion, and extremely low pollutant emissions, due to the zero-carbon content. Nevertheless, NOx emissions are still an issue in hydrogen fueled engines and optimized lean-burn combustion and suitable after-treatment NOx reduction are mandatory to reach high specific power and efficiency and near zero NOx emissions, thus enabling H2-ICE powered vehicles to be zero-impact emitting technology solution.</div><div class="htmlview paragraph">Selective Catalytic Reduction by using NH3 as the reducing agent is the most effective control technology for NOx abatement. Nevertheless, ongoing research and innovation are critical in developing new strategies for reducing NOx emissions, to overcome the NH3-SCR system main critical issues (extra equipment for urea storage and dosing, ammonia-slip, deactivation and fouling, low efficiency at low temperature).</div><div class="htmlview paragraph">The SCR of NOx by hydrogen is considered a promising alternative to traditional ammonia-based deNOx technology. The H2-SCR catalysts are suitable for engine exhaust after-treatment during cold-start and urban-driving operations, exhibiting higher catalytic activity for low-temperature NOx emissions conversion (180 – 200 °C). Furthermore, in H2-ICE powered vehicles, the additional tank to store the reducing agent is not needed with a significant simplification of the engine exhaust lay-out.</div><div class="htmlview paragraph">Experimental investigations on different H2-SCR catalysts have demonstrated that the conversion activity is greatly affected by the catalytic system configuration, the adsorption properties of the support material, the H2 spillover, that in turn are affected by H2/NO ratio and exhaust gas composition, temperature and flow rate.</div><div class="htmlview paragraph">In the present paper, a feed-forward neural network model of H2-SCR is presented, with the aim of performing real-time estimation of reduction efficiency and supporting the design of suitable H2 management to achieve maximum NOx reduction and minimum hydrogen consumption. Model training and identification are carried out against a large set of experimental data measured on a H2-SCR small scale prototype at the Synthetic Gas Bench. The experimental tests were designed to reproduce the real conditions expected at the exhaust of a H2-fueled engine.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The Diesel engine combustion process results in harmful exhaust emissions, mainly composed of Particulate Matter (PM), Hydro Carbon (HC), Carbon monoxide (CO) and Nitrogen Oxides (NO<sub>x</sub>). Several technologies have been developed in the past decades to control these diesel emissions. One of the promising and well matured technology of reducing NO<sub>x</sub> is to implement Selective Catalytic Reduction (SCR) using ammonia (NH<sub>3</sub>) as the reducing agent. For an effective SCR system, the aqueous urea solutions should be fully decomposed into ammonia and it should be well distributed across the SCR. In the catalyst, all the ammonia is utilized for NO<sub>x</sub> reduction process. In the design stage, it is more viable to implement Computational Fluid Dynamics (CFD) for design iterations to determine an optimized SCR system based on SCR flow distribution. And in later stage, experimental test is required to predict the after-treatment system performance based on NO<sub>x</sub> reduction.</div><div class="htmlview paragraph">The SCR model predicts the NH<sub>3</sub> formation from urea decomposition and it is quantified at the SCR inlet, whereas experimental data involves the NO<sub>x</sub> reduction process. In order to validate the numerical predictions, the modeling needs to include surface reactions happening in the SCR catalyst bed. There are many factors that affect NO<sub>x</sub> conversion process, such as exhaust temperature, NO<sub>2</sub>/NO<sub>x</sub> ratio, catalyst coating, oxidation, etc. To model SCR Kinetics, various input parameters are required and also the reaction process needs to be well defined. The objective of this work is to conduct urea SCR spray modeling studies to focus on these input parameters and to observe its influence over NO<sub>x</sub> reduction process.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Selective Catalytic Reduction (SCR) catalysts used in Lean NO<sub>x</sub> Trap (LNT) - SCR exhaust aftertreatment systems typically encounter alternating oxidizing and reducing environments. Reducing conditions occur when diesel fuel is injected upstream of a reformer catalyst, generating high concentrations of hydrogen (H₂), carbon monoxide (CO), and hydrocarbons to deNO<sub>x</sub> the LNT. In this study, the functionality of an iron (Fe) zeolite SCR catalyst is explored with a bench top reactor during steady-state and cyclic transient SCR operation.</div><div class="htmlview paragraph">Experiments to characterize the effect of an LNT deNO<sub>x</sub> event on SCR operation show that adding H₂ or CO only slightly changes SCR behavior with the primary contribution being an enhancement of nitrogen dioxide (NO₂) decomposition into nitric oxide (NO). Exposure of the catalyst to C₃H₆ (a surrogate for an actual exhaust HC mixture) leads to a significant decrease in NO<sub>x</sub> reduction capabilities of the catalyst. A degradation mechanism is proposed to account for the decrease in NO<sub>x</sub> conversion efficiency, highlighted by reactions between NO₂ and C₃H₆ to make NO at a rate of similar order of magnitude as the Fast SCR reaction. This inhibits SCR reactions when the NO:NO<sub>x</sub> ratio favors NO, but can increase NO<sub>x</sub> conversion when the NO:NO<sub>x</sub> ratio favors NO₂.</div><div class="htmlview paragraph">Ammonia (NH₃) storage is only marginally affected by the presence of H₂, CO, or C₃H₆; but significant amounts of C₃H₆ can be stored on the catalyst. Further observation reveals that the oxidation effects of C₃H₆ are non-negligible and C₃H₆ strongly influences the oxidation of NH₃. The degradation mechanism includes seven proposed reactions to model the experimental results of adding H₂, CO, and C₃H₆ to the SCR feed gas during steady-state and transient operation.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Advanced exhaust after-treatment technology is required for heavy-duty diesel vehicles to achieve stringent Euro VI emission standards. Diesel particulate filter (DPF) is the most efficient system that is used to trap the particulate matter (PM), and particulate number (PN) emissions form diesel engines. The after-treatment system used in this study is catalyzed DPF (CDPF) downstream of diesel oxidation catalyst (DOC) with secondary fuel injection. Additional fuel is injected upstream of DOC to enhance exothermal heat which is needed to raise the CDPF temperature during the active regeneration process.</div><div class="htmlview paragraph">The objective of this research is to numerically investigate soot loading and active regeneration of a CDPF on a heavy-duty diesel engine. In order to improve the active regeneration performance of CDPF, several factors are investigated in the study such as the effect of catalytic in filter wall, soot distribution form along filter wall, and soot loads. This paper also presents simulation results of temperature, pressure, and soot distribution in the CDPF.</div><div class="htmlview paragraph">The after-treatment model is validated by comparing the simulation results with the measured data, and small deviation is obtained between the measured data and numerical results. Soot loading simulation indicates that soot accumulation is non-uniform along the CDPF, where higher soot accumulation at the end of filter monolith is observed. Moreover, the lowest soot accumulation occurs in the region near CDPF entrance. 3D contour images of regeneration simulation show that the soot oxidation rate of the filter increases when accumulated soot mass increases and temperature profile increases. Simulation results of catalyzed DPF (CDPF) reveal that additional exothermic reaction on wall improves the regeneration performance.</div></div>

<div class="section abstract"><div class="htmlview paragraph">As vehicle emissions regulations become increasingly stringent, there is a growing need to accurately model aftertreatment systems to aid in the development of ultra-low NOx vehicles. Common solutions to this problem include the development of complex chemical models or expansive neural networks. This paper aims to present the development process of a simpler Selective Catalytic Reduction (SCR) conversion efficiency Simulink model for the purposes of modeling tail pipe NOx emission levels based on various inputs, temperature shifts and SCR locations, arrangements and/or sizes in the system. The main objective is to utilize this model to predict tail pipe NOx emissions of the EPA Federal Test Procedures for heavy-duty vehicles. The model presented within is focused exclusively on heavy-duty application compression ignition engines and their corresponding aftertreatment setups. The accuracy of the model depends heavily on the ability to gain precise and repeatable test cell data to calculate an expansive SCR conversion efficiency map for the given aftertreatment system. This conversion efficiency map is verifiable based on expected/known chemical and physical properties of SCR aftertreatment systems. For this application, a 2-dimensional map was created, using SCR temperature and space velocity. The model requires several inputs including engine out NOx concentrations, SCR temperature, and exhaust flow/space velocity to input into the table and thus predict the corresponding tail pipe NOx. While different engine calibrations can impact the accuracy of the model, it was found that error in average tail pipe NOx prediction (g/bhp·hr) was approximately +/- 10%. For the purposes of this model, this error was found to be sufficient in providing the proper direction for ultra-low NOx aftertreatment development.</div></div>

<div class="htmlview paragraph">For diesel applications, cold start accounts for a large amount of the total NO<sub>x</sub> emissions during a typical Federal Test Procedure (FTP) for light-duty vehicles and is a key focus for reducing NO<sub>x</sub> emissions. A common form of diesel NO<sub>x</sub> aftertreatment is selective catalytic reduction (SCR) technology. For cold start NO<sub>x</sub> improvement, the SCR catalyst would be best located as the first catalyst in the aftertreatment system; however, engine-out hydrocarbons and no diesel oxidation catalyst (DOC) upstream to generate an exotherm for desulfation can result in degraded SCR catalyst performance. Recent advances in vanadia-based SCR (V-SCR) catalyst technology have shown better low temperature NO<sub>x</sub> performance and improved thermal durability. Three V-SCR technologies were tested for their thermal durability and low-temperature NO<sub>x</sub> performance, and after 600°C aging, one technology showed low-temperature performance on par with state-of-the-art copper-zeolite SCR (Cu-SCR) technology. This V-SCR catalyst was further compared with the Cu-SCR technology for hydrocarbon tolerance, sulfur tolerance, and ammonia storage capacity. The V-SCR technology had similar hydrocarbon tolerance, superior sulfur tolerance, and less ammonia storage than the Cu-SCR catalyst.</div>