Diesel Aftertreatment Systems Research Articles

Catalytic activity of Zr/CeO2-Al2O3 catalyst for diesel soot oxidation: synthesis, characterization, and performance evaluation.

Diesel soot is a significant contributor to air pollution. Soot particles present in diesel engine exhaust have a negative impact on the environment and human health. Diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) currently use noble metal-based catalysts for soot oxidation. Due to the use of noble metals in the catalyst, the cost of diesel after-treatment systems is steadily rising. As a result, diesel vehicles have become commercially less viable than gasoline vehicles and electronic vehicles. The study focuses on an alternative diesel oxidation catalyst with efficiency similar to that of a noble metal catalyst but with a much lower cost. CeO2-Al2O3 catalysts are known for their oxygen storage capacity and high redox activity, making them suitable for soot oxidation. Adding Zr to these catalysts has been shown to influence their structural and chemical properties, significantly affecting their catalytic behavior. Therefore, the current study is focused on using Zr/CeO2-Al2O3 as a substitute for noble metal-based catalysts to enhance its performance for diesel soot oxidation in automotive exhaust. Evaporation-induced self-assembly (EISA) was used to prepare 1, 3, and 5 weight (wt) % Zr supported mesoporous CeO2-Al2O3 catalysts. Morphological, structural, and physicochemical properties of the synthesized catalysts were examined using Brunauer-Emmett-Teller (BET) absolute isotherm, Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Temperature programmed reduction (TPR), and Temperature-programmed desorption of ammonia (NH3-TPD). XRD, BET, and SEM data confirmed that the catalysts were mesoporous and low-crystalline with a high surface area. The soot oxidation activity of the catalysts was evaluated using a thermogravimetric analysis (TGA) technique. The loose contacts soot oxidation activity test suggested that 50% oxidation of soot occurred at 390°C in the absence of a catalyst. T50 of CeO2-Al2O3 catalyzed soot oxidation was 296°C. Adding Zr to the catalyst significantly improved catalytic activity for diesel soot oxidation. We observed a further drastic change in T50 of soot over 1, 3, and 5% Zr/CeO2-Al2O3, which were 220°C, 210°C, and 193°C, respectively. According to these results, incorporating Zr into the CeO2-Al2O3 catalyst significantly improved the oxidation process of soot.

The impact on passenger car emissions associated with the promotion and demise of diesel fuel

The promotion and growth in the use of diesel fuel in passenger cars in the UK and Europe over the past two decades led to considerable adverse air quality impacts in urban areas and more widely. In this work, we construct a multi-decade analysis of passenger car emissions in the UK based on real driving emissions data. An important part of the study is the use of extensive vehicle emission remote sensing data covering multiple measurement locations, time periods, environmental conditions and consisting of over 600,000 measurements. These data are used to consider two scenarios: first, that diesel fuel use was not promoted in the early 2000s for climate mitigation reasons, and second, that there was not a dramatic decline in diesel fuel use following the Dieselgate scandal. The strong growth of diesel fuel use coincided with a time when diesel NOx emissions were high and, conversely, the strong decrease of diesel fuel use coincided with a time when diesel vehicle after-treatment systems for NOx control were effective. We estimate that the growth in diesel car use in the UK results in excess NOx emissions of 721 kt over a three decade period; equivalent to over 7 times total annual passenger car NOx emissions and greater than total UK NOx emissions of 681.8 kt in 2021 and with an associated damage cost of £5.875 billion. However, the sharp move away from diesel fuel post-Dieselgate only reduced NOx emissions by 41 kt owing to the effectiveness of modern diesel aftertreatment systems.

Influence of the engine drop-to-idle process on regeneration temperature, filtration and morphology characteristics of diesel particulate filters

As emission regulations become more stringent, the durability of diesel aftertreatment system is a concern in addition to its purification capacity. Under extreme circumstances, the engine may drop-to-idle (DTI) sharply, which can cause the diesel particulate filter (DPF) cracking and melting during active regeneration due to the excessive soot combustion heat. This study investigated the regeneration performance of cordierite DPFs during the DTI process, including temperature and emission characteristics. The temperature distribution is nonuniform, with the peak temperature occurring in the middle ring of the DPF monolith’s rear end. As the soot load reached 7 g/L, extensive DPF cracks were observed and the particle number (PN) emission exceeded the regulatory limit. The study also examined the evolution of the DPF's porous wall’s macro morphology and micro pore structure, finding that microcracks formed and the wall surface became rougher. The substrate’s bulk density, average pore diameter, and permeability decreased while the total pore volume, total pore area, tortuosity, and porosity increased. By analyzing temperature, filtration and morphology characteristics, this work provides a recommended soot mass limit (SML) for cordierite DPF, which is essential for developing a reliable regeneration strategy in diesel vehicle control systems. The findings also help with the optimization design of substrate and catalysts for manufacturers in terms of substrate material, filter geometry, cell density and catalyst coating.

Kinetic modeling of NH3-selective catalytic reduction (SCR) over a mildly hydrothermally aged commercial Cu-SSZ-13 catalyst

Cu-SSZ-13 is often studied as a selective catalytic reduction (SCR) of NOx catalyst for diesel after-treatment systems. Mild hydrothermal aging (HTA) is commonly known to cause changes in catalyst performance. In this study, a kinetic model of SCR over a Cu-SSZ-13 catalyst that includes mild HTA and its impact on the SCR reaction was developed. The migration of Cu species during HTA, and how this change in Cu distribution affects low-temperature and high-temperature NH3 oxidation and SCR reaction mechanisms, were considered. Flow reactor test results were used for parameter estimation and verification. Different characterization techniques, including H2 temperature-programmed reduction (H2-TPR), NO + NH3-TPR, NH3 temperature-programmed desorption (NH3-TPD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), were used to characterize and quantify catalyst site densities. The model can simulate the migration of Cu species and the NOx reduction performance changes during mild hydrothermal aging as a function of aging temperature and time.

Excellent hydrocarbon tolerance of CeO2-WO3-SnO2 oxide catalyst for the NH3-SCR of NO

The tolerance of NH3-SCR catalysts towards hydrocarbon compounds (HCs) is very important for their practical application on diesel vehicles. In this study, the HC resistance of CeWSnOx, V2O5-WO3/TiO2 and Cu-SSZ-13 catalysts was systematically investigated using propene, toluene and n-pentane as model HCs. Experimental results suggested that the fresh and hydrothermally aged CeWSnOx showed much better HC tolerance than the Cu-SSZ-13 and V2O5-WO3/TiO2. This property mainly originated from the strong HC oxidation capacity of the CeWSnOx due to Sn introduction, which significantly inhibited side reactions, including the HC ammoxidation and the carbon deposition reactions. In contrast, an undesired HC ammoxidation reaction occurred at medium temperatures over the Cu-SSZ-13 and at medium-high temperatures over V2O5-WO3/TiO2, especially in the presence of propene, accompanied by the emission of toxic HCN gas. The high HC tolerance of CeWSnOx gives it promise for application on heavy-duty diesel after-treatment systems in the future, especially those with the SCR-on-DPF or cc-SCR configuration.

Data-Based On-Board Diagnostics for Diesel Engine NOx-Reduction Aftertreatment Systems

Abstract The NOx conversion efficiency of a combined selective catalytic reduction and ammonia slip catalyst (SCR-ASC) in a diesel aftertreatment (AT) system degrades with time. A novel model-informed data-driven on-board diagnostic (OBD) binary classification strategy is proposed in this paper to distinguish an end of useful life (EUL) SCR-ASC catalyst from degreened (DG) ones. An optimized, supervised machine learning model was used for the classification with a calibrated single-cell three-state continuous stirred tank reactor (CSTR) observer used for state estimation. Percentage of samples classified as EUL (%EUL), with respect to classification boundary of 50%, was used as an objective criterion of classification. The method resulted in 87.5% classification accuracy when tested on eight day-files from four trucks (2 day-files per truck; 1 DG and 1 EUL) operating in real-world on-road conditions. Each day-file had ∼86,000 samples of data. Mileage of the same truck was used as ground truth for classification. However, mileage across different trucks cannot be used for classification since the operating conditions would vary across trucks.

Application of Model-Based Controller on a Heavy-Duty Dual Selective Catalytic Reduction Aftertreatment

<div>Commercial vehicles require advanced engine and aftertreatment (AT) systems to meet upcoming nitrogen oxides (NO<sub>x</sub>) and carbon dioxide (CO<sub>2</sub>) regulations. This article focuses on the development and calibration of a model-based controller (MBC) for an advanced diesel AT system. The MBC was first applied to a standard AT system including a diesel particulate filter (DPF) and selective catalytic reduction (SCR) catalyst. Next, a light-off SCR (LO-SCR) was added upstream of the standard AT system. The MBC was optimized for both catalysts for a production engine where the diesel exhaust fluid (DEF) was unheated for both SCRs. This research shows that the tailpipe (TP) NO<sub>x</sub> could be reduced by using MBC on both catalysts. The net result was increased NO<sub>x</sub> conversion efficiency by one percentage point on both the LO-SCR and the primary SCR. The CO<sub>2</sub> emissions were slightly reduced, but this effect was not significant. Finally, the MBC was used with a final setup representative of future AT systems which included standard insulation on the catalysts and optimal DEF dosing controls. This final configuration resulted in an improved NO<sub>x</sub> and CO<sub>2</sub> such that the composite Federal Test Procedure (FTP) NO<sub>x</sub> was 0.060 g/hp-hr and the composite FTP CO<sub>2</sub> was 508.5 g/hp-hr. The article details this cycle along with the low-load cycle (LLC) and beverage cycle. More technologies are required to meet the future California Air Resources Board (CARB) 2027 standard, which will be shown in future work.</div>

Single Ru(II) Ions on Ceria as a Highly Active Catalyst for Abatement of NO.

Atom trapping leads to catalysts with atomically dispersed Ru1O5 sites on (100) facets of ceria, as identified by spectroscopy and DFT calculations. This is a new class of ceria-based materials with Ru properties drastically different from the known M/ceria materials. They show excellent activity in catalytic NO oxidation, a critical step that requires use of large loadings of expensive noble metals in diesel aftertreatment systems. Ru1/CeO2 is stable during continuous cycling, ramping, and cooling as well as the presence of moisture. Furthermore, Ru1/CeO2 shows very high NOx storage properties due to formation of stable Ru-NO complexes as well as a high spill-over rate of NOx onto CeO2. Only ∼0.05 wt % of Ru is required for excellent NOx storage. Ru1O5 sites exhibit much higher stability during calcination in air/steam up to 750 °C in contrast to RuO2 nanoparticles. We clarify the location of Ru(II) ions on the ceria surface and experimentally identify the mechanism of NO storage and oxidation using DFT calculations and in situ DRIFTS/mass spectroscopy. Moreover, we show excellent reactivity of Ru1/CeO2 for NO reduction by CO at low temperatures: only 0.1-0.5 wt % of Ru is sufficient to achieve high activity. Modulation-excitation in situ infrared and XPS measurements reveal the individual elementary steps of NO reduction by CO on an atomically dispersed Ru ceria catalyst, highlighting unique properties of Ru1/CeO2 and its propensity to form oxygen vacancies/Ce+3 sites that are critical for NO reduction, even at low Ru loadings. Our study highlights the applicability of novel ceria-based single-atom catalysts to NO and CO abatement.

Burner based thermal management approach utilizing in-exhaust burner technology with a CDA equipped engine

Commercial vehicles require fast aftertreatment heat-up to move the SCR catalyst into the most efficient temperature range to meet upcoming NOX regulations while minimizing CO2. One solution to this challenge is to add a fuel burner upstream of the con`ventional heavy-duty diesel aftertreatment system. The focus of this paper is to optimize a burner based thermal management approach. The objective included complying with CARB’s 2027 low NOX emissions standards for on-road heavy duty diesel engines. This was accomplished by pairing the burner system with cylinder de-activation on the engine and/or a light-off SCR sub-system. A system solution is demonstrated using a heavy-duty diesel engine with an aged aftertreatment system targeted for 2027 emission levels using various levels of controls. The baseline layer of controls includes cylinder deactivation to raise the exhaust temperature more than 100°C in combination with elevated idle speed to increase the mass flowrate through the aftertreatment system. The combination of operating the fuel burner, cylinder deactivation and elevated idle speed (during cold start) allows the aftertreatment system to heat up in a small fraction of the time demonstrated by today’s systems. Performance was quantified over the cold FTP, hot FTP, low load cycle (LLC) and the U.S. beverage cycle. The improvement in NOX reduction and the CO2 savings over these cycles are highlighted.

A New Electrically Heated Mixer (EHM) for Efficient SCR of NOx in Low Load Cycles

<div class="section abstract"><div class="htmlview paragraph">Low temperature Diesel exhaust operations such as during low-load cycles are some of the most difficult conditions for SCR of NOx. This, along with newer regulations targeting substantial reduction of the tailpipe NOx such as California-2024/2027 NOx regulations, adds to challenges of high efficiency SCR of NOx in low temperature operations. A novel design, low-cost, low-energy Electrically Heated Mixer (EHM™), energized via the 12, 24 or 48 V vehicle electrical system, is used to accelerate formation of reductants (ammonia, isocyanic acid) in low temperature exhaust (low load cycles), so to enable high efficiency SCR of NOx in most challenging SCR conditions, while also mitigating urea deposit formation. EHM™ is also used to heat the cooler exhaust flow during engine cold-start. It easily fits common exhaust configurations and can be utilized on light, medium or heavy duty Diesel aftertreatment systems, on- or non-road or in stationary systems.</div></div>

Analysis on the potential of EGR strategy to reduce fuel consumption in hybrid powertrains based on advanced gasoline engines under simulated driving cycle conditions

The increased concern for environmental problems has boosted the electrification of passenger cars to remove air pollutant emissions from urban areas. Automotive manufacturers have predominantly opted for hybrid powertrains with advanced gasoline engines, because of the current limitations of battery electric vehicles and the higher costs of diesel aftertreatment systems. Meanwhile, the exhaust gas recirculation (EGR) strategy decreases fuel consumption and CO2 emissions in gasoline engines. The powertrain hybridization may increase the EGR benefit in fuel consumption, given that the dependence of internal combustion engine (ICE) operation on the driver’s power demand is reduced. The ICE can usually operate at medium loads, around its maximum efficiency zone, where the EGR benefit is greater than at low loads. Therefore, this research aimed to quantify the fuel saving achieved with EGR in a gasoline-electric hybrid powertrain under driving cycle conditions. To this end, vehicle 0D simulations were performed using a map-based engine fuel consumption model. Engine tests and 1D simulations were carried out to obtain ICE fuel maps with and without EGR. Besides, the transient performance of the vehicle 0D model was validated with experimental data. Both rule- and optimization-based strategies were used to manage the power split between the engine and electric motor. Modeling results revealed that EGR improves fuel economy by 4.6% in the hybrid powertrain during a WLTP class 3b driving cycle, 2% more than in the conventional one.

Initial Results on a New Light-Duty 2.7-L Opposed-Piston Gasoline Compression Ignition Multi-Cylinder Engine

Abstract Gasoline compression ignition (GCI) is a cost-effective approach to achieving diesel-like efficiencies with low emissions. The fundamental architecture of the two-stroke Achates Power Opposed-Piston (OP) Engine enables GCI by decoupling piston motion from cylinder scavenging, allowing for flexible and independent control of cylinder residual fraction and temperature leading to improved low-load combustion. In addition, the high peak cylinder pressure and noise challenges at high-load operation are mitigated by the lower brake mean effective pressure (BMEP) operation and faster heat release for the same pressure rise rate of the OP Engine. These advantages further solidify the performance benefits of the OP Engine and demonstrate the near-term feasibility of advanced combustion technologies, enabled by the opposed-piston architecture. This paper presents initial results from steady-state testing on a brand new 2.7-L OP GCI multi-cylinder engine (MCE) designed for light-duty truck applications. Successful GCI operation calls for a high compression ratio (CR), leading to higher combustion stability at low loads, higher efficiencies, and lower cycle HC + NOX emissions. Initial results show a cycle average brake thermal efficiency (BTE) of 31.7%, which is already greater than 11% conventional engines, after only ten weeks of testing. Emissions results suggest that Tier 3 Bin 160 levels can be achieved using a traditional diesel after-treatment system. Combustion noise was well controlled at or below the United States Council for Automotive Research limits. In addition, initial results on catalyst light-off mode with GCI are also presented.

Nitrous oxide in diesel aftertreatment systems including DOC, DPF and urea‐SCR

The formation of Nitrous oxide (N2O) over urea-based selective catalytic reduction (SCR) systems was scrutinized using exhaust gases from a 3.4-liter non-road diesel engine. Four catalysts were used for the SCR systems; Cu-zeolite (Cu/Fe = 4), Fe-zeolite (Fe only), vanadia and mixed (vanadia and Cu-zeolite) one. For all SCR systems, the N2O concentration at the SCR inlet (before SCR) was below 1 ppm, except for the low-load and low-speed engine conditions, where it was below 3 ppm. However, at the SCR outlet, the N2O concentration had risen to nearly 20 ppm, except for a few conditions. That is, N2O increased more than a dozen times by passing through the SCR systems. The amount of N2O formed within the SCR systems depended on the SCR catalysts; the vanadia catalyst had the lowest amount of N2O, while the Fe-zeolite catalyst as well as the Cu-zeolite catalyst had the highest. In addition, the formation of N2O was strongly involved in the ratio of nitrogen dioxide (NO2) to nitrogen oxides (NOx) at the SCR inlet, which was coupled to SCR inlet temperatures. The higher ratio of NO2 to NOx led to higher N2O at the SCR outlet. It was found that the start of N2O formation corresponded to the moment when nitric oxide (NO) was close to 0 ppm as the ratio of an ammonia (NH3) in aqueous urea solution to NOx increased. In other words, NO depletion played a crucial role in the start of N2O formation when NO and NO2 were simultaneously consumed. Therefore, the difference in N2O formation among the four catalysts for the SCR systems depended on how quickly NO was depleted. Results from α values of intersections of N2O and NO (α@N₂O = NO) for Cu- and Fe-zeolite catalysts showed that α@N₂O = NO for the Fe-zeolite catalyst are much smaller than that for the Cu-zeolite catalyst, and this implies that the Fe-zeolite catalyst can start N2O formation earlier or have faster NO depletion than the Cu-zeolite catalyst.

Impact of Water Vapor on the Performance of a Cu-SSZ-13 Catalyst under Simulated Diesel Exhaust Conditions

<div class="section abstract"><div class="htmlview paragraph">Cu-SSZ-13 selective catalytic reduction (SCR) catalysts are broadly applied in diesel aftertreatment systems for the catalytic conversion of oxides of nitrogen (NO + NO<sub>2</sub>). Diesel exhaust contains a wide range of water vapor concentrations depending on the operating condition. In this study, we evaluate the impact of water vapor on the relevant SCR catalytic functions including NO<sub>x</sub> conversion, NO oxidation, NH<sub>3</sub> oxidation, and N<sub>2</sub>O formation under both standard and fast SCR conditions. Reactor-based experiments are conducted in the presence and absence of water vapor. Results indicate that water vapor can have both a positive and negative impact on low temperature NO<sub>x</sub> conversion for standard SCR reaction. At low inlet NO<sub>x</sub> concentrations, the presence of water vapor has a negative effect on NO<sub>x</sub> conversion, whereas, at high inlet NO concentrations, water vapor improves NO<sub>x</sub> conversion. At high temperatures, water vapor has a beneficial effect on NO<sub>x</sub> conversion at all NO<sub>x</sub> inlet concentrations evaluated. Experiments under fast SCR conditions reveal that water vapor improves low temperature NO<sub>x</sub> conversion mainly by minimizing the accumulation of ammonium nitrate, as evidenced with temperature programmed desorption (TPD) results. Furthermore, NO oxidation by ammonium nitrate formed under fast SCR conditions is shown to be significantly faster in the presence of water vapor.</div></div>

Study on characteristics of particulate emission of diesel aftertreatment with reciprocating flow

AbstractIn this article, in order to optimize diesel aftertreatment system with periodically reciprocating flow (PRF), an experimental study is conducted to investigate its characteristics such as pollution emissions, regeneration of diesel particulate filter (DPF), concentration, and size distribution of particulate matter (PM) escaped as well as temperature distribution under unidirectional flow and PRF operating conditions. The effects of reciprocating flow cycle and exhaust gas flow on the performance of aftertreatment system are investigated in detail. The energy efficiency analysis of the aftertreatment system is also carried out. Experimental results show that (a) as the temperature is lower than the light‐off threshold of combustible gas, the aftertreatment system cannot restrain the formation of second particles under the low‐temperature condition of unidirectional flow; and (b) the aftertreatment system demonstrates excellent performance of trapping particles and filter regeneration as the symmetrical temperature distribution is formed. The PM filter efficiency is 92%, and the specific energy consumption β is 124% for symmetrical temperature distribution; (c) the increase in reciprocating flow cycle could lead to the shifting of the temperature profiles, and this would affect the particle size distribution; (d) a certain increase in exhaust gas flow from engine would have insignificant change for the temperature distribution; and (e) the critical energy efficiency of the system could reach 96.61%.

Boosting NOx Removal by Perovskite-Based Catalyst in NSR–SCR Diesel Aftertreatment Systems

A detailed analysis of the DeNOx activity of the novel 0.5% Pd-30% La0.5Ba0.5CoO3/Al2O3 formulation in its application to the single-NSR and combined NSR–SCR systems is carried out using response s...

Effects of Oxygenated Biomass Fuels on the Performance of Diesel Engine and After-Treatment System

Abstract Oxygenated biomass fuels have attracted significant attention due to their contributions in reducing environmental pollution and fossil fuel consumption. In view of stricter emission regulations, the use of these alternative fuels cannot fully meet the requirements, and it needs to be combined with an after-treatment system. In this article, polymethoxy dimethyl ether (PODE) and n-pentanol were blended with diesel (D100 (pure diesel)) at 15% and 20% by volume, respectively, referred to as D85P15, D80P20, D85A15, and D80A20, while the effects of the addition of two new oxygenated biomass fuels on the performance of diesel engine and diesel oxidation catalyst (DOC) and catalytic diesel particulate filter (CDPF) after-treatment system were experimentally investigated. Results show that the addition of oxygenated biomass fuels can improve combustion and reduce carbon monoxide (CO) and soot emissions. At heavy load conditions, when D80P20 was used, compared with D100 and D80A20, the conversion efficiency of CO emissions in DOC + CDPF system is always the highest, close to 100%. It shows that the addition of oxygenated biomass fuels can effectively improve the exhaust oxygen concentration. Besides, there is nearly no increase in CDPF pressure drop at each tested engine speed when D80P20 is used. This has greatly improved in CDPF performance.

Performance of a conventional diesel aftertreatment system used in a medium-duty multi-cylinder dual-mode dual-fuel engine

Dual-mode dual-fuel combustion stands as one of the promising techniques to allow the dual-fuel operation along the whole engine map. This concept relies on using different combustion strategies as reactivity controlled compression ignition up to medium load, then migrating to diffusive dual-fuel combustion to reach full load. With this strategy, it is possible to obtain sensible reductions in NOx and soot while providing improvements in fuel consumption and CO2 emissions. However, the excessive quantities of HC and CO together with the low exhaust temperature can compromise the diesel oxidation catalyst (DOC) efficiency. In addition, the diffusive dual-fuel combustion applied at high engine load produces considerable soot amounts that should be reduced within the diesel particulate filter (DPF).Based on these facts, this work intends to evaluate the efficiency of a commercial aftertreatment system (DOC + DPF) while operating in dual-mode dual-fuel combustion. Additionally, fundamental studies where developed to understand the impact of the combination of fuels on the exhaust hydrocarbon species. First, the DOC performance was evaluated at steady-state and transient conditions under different operating conditions fulfilling the EUVI NOx and soot limits. In parallel, the different engine-out hydrocarbon species were measured by means of a Fourier-transform infrared spectroscopy (FTIR) gas analyzer. Finally, the passive and active regeneration processes were assessed by means of different methodologies aiming to evaluate the low NOx-low soot interaction and the capability of the active regeneration in dual-fuel dual-mode (DMDF) operating conditions. The DOC results showed an improper conversion efficiency at low load operating condition, where the exhaust temperature is low. By contrast, the thermal inertia at transient conditions allowed to improve the DOC behavior at low load, reaching DOC-out emissions one order of magnitude lower than those from the steady-state tests. Concerning the DPF, it was demonstrated that the low concentration of NOx and soot produced during the combustion does not lead to sensible changes in the NO2/NOx ratio before and after the DPF, indicating a low level/absence of passive regeneration. In the case of the active regeneration, both conventional diesel combustion (CDC) and DMDF operating conditions can obtain satisfactory reduction in the total soot trapped, being the increase in the exhaust temperature consequence of the HC and CO conversion the supporting mechanism for the active regeneration in the DMDF concept.

Cold-Start WHTC and WHSC Testing Results on Multi-Cylinder Opposed-Piston Engine Demonstrating Low CO <sub>2</sub> Emissions while Meeting BS-VI Emissions and Enabling Aftertreatment Downsizing

<div class="section abstract"><div class="htmlview paragraph">Reducing the greenhouse emissions from on-road freight vehicles to meet the climate change mitigation objectives, has become a prime focus of regulatory authorities all over the world. Besides India, the United States, the European Union, Canada, Japan, and China have already established or planned heavy-duty vehicle efficiency regulations addressing CO<sub>2</sub> and NO<sub>X</sub> emissions. In addition, Argentina, Brazil, Mexico, and South Korea are all in various stages of developing policies to improve the efficiency of their commercial vehicle fleets. For CO<sub>2</sub> emissions reduction standards, the U.S. mandates 27% reduction by 2027, EU is calling for 15% reduction by 2025, China for 27% by 2019 over 2012 levels, and India is mandating 10%-15% reduction by 2021 for phase 2 of the new standard. There has also been considerable focus on further reduction in NO<sub>X</sub> emissions from current levels (0.2 g/hp-hr), to the proposed ultra-low NOx standards (0.02 g/hp-hr) in the U.S. for heavy duty engines by 2024.</div><div class="htmlview paragraph">Given these planned and proposed regulatory standards being implemented around the globe, there have been substantial studies and publications focusing on exploring and evaluating technologies that can help deliver the lower tailpipe NOx targets and understand the CO<sub>2</sub> impact associated with it. Majority of the NO<sub>X</sub> emissions from engine, occur during the cold-start portion of the transient regulatory cycles, like HD FTP and WHTC. This is because, a typical heavy-duty diesel aftertreatment system does not achieve substantial NO<sub>X</sub> reduction until approximately 400-500 seconds into the cold-start cycle due to lack of heat from the engine. The result is untreated NOx escaping through to tailpipe. To achieve low NOx emission levels over the composite transient cycles, the engine must provide rapid exhaust heat energy, during the cold-start portion, to reduce the time required by the SCR catalyst to reach catalyst light-off temperature, while controlling the NO<sub>X</sub> emissions. Moreover, high NO<sub>X</sub> conversion efficiency must be maintained during the hot-start portion of cycle. For a conventional heavy-duty engine, providing rapid exhaust heat while controlling NOx emissions has been a challenge, because these are competing demands. Implementing secondary or auxiliary heat sources downstream in the exhaust after treatment system (ATS) comes at CO<sub>2</sub> penalty and adds significant cost and complexity. This has been established in recent publications by organization like SwRI [<span class="xref">1</span>], CARB and Bosch [<span class="xref">2</span>].</div><div class="htmlview paragraph">Achates Power Opposed Piston (OP) engine technology provides ideal solution to this challenge. The opposed-piston engine has several inherent advantages over conventional four-stroke engines, like higher BTE (15-30% higher), higher power density, an air-system that results in reduced pumping work, the ability to control residual combustion gases, two fuel injectors per cylinder providing greater timing flexibility, and the ability to provide rapid engine out heat and temperature rise for the exhaust emission system while maintaining low engine out NO<sub>X.</sub></div><div class="htmlview paragraph">This paper demonstrates results from cold and hot start transient WHTC testing and WHSC testing, conducted at Achates Power, on a three-cylinder opposed-piston engine. Results show that the Achates Power OP Engine can deliver engine out heat and temperature rise that exceeded and sustained catalyst light-off temperature thresholds (250°C) within the first 60-100 seconds in the cold start cycle, while controlling engine out NOx to lower levels when compared to a conventional four-stroke heavy-duty diesel engine. As a result, the OP Engine not only meets current BS-VI and future regulatory emissions requirements but is also able to do so with a significant CO<sub>2</sub> emissions advantage. Furthermore, the inherent advantages of the OP Engine offer unique aftertreatment optimization and downsizing opportunities thereby enabling cost reduction.</div></div>

Modeling and Analytical Solutions for Optimal Heating of Aftertreatment Systems

Abstract Cold start emissions are the most significant contributor to the accumulated emissions of a vehicle and poses a critical design limit for the design of clean and efficient vehicles. The core reasons for the emissions are the initial low temperature and the thermal inertia of the exhaust aftertreatment systems. Moreover, it also costs fuel to perform the heating of the catalyst. It is therefore of high interest to develop efficient control schemes that can reduce the time to light off. To facilitate this a model structure and a method, based on the explicit solution to the catalyst differential equations are developed, that can be used to analyze both time and fuel optimal heating control strategies. The method is developed to be applicable to both gasoline and diesel aftertreatment systems. A case study is performed on a Diesel engine and the results show that the solutions exhibit a structured and simple two-phase pattern. There is a first heating phase, where the catalyst is fed with a high temperature gas, building up a high inlet temperature. Then in a second phase the flow is kept high and the temperature is pushed through the catalyst. The strategy is easy to understand and realize in a real time control system.