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Technical Paper

A Modeling Analysis of Fibrous Media for Gasoline Particulate Filters

2017-03-28
2017-01-0967
With an emerging need for gasoline particulate filters (GPFs) to lower particle emissions from gasoline direct injection (GDI) engines, studies are being conducted to optimize GPF designs in order to balance filtration efficiency, backpressure penalty, filter size, cost and other factors. Metal fiber filters could offer additional designs to the GPF portfolio, which is currently dominated by ceramic wall-flow filters. However, knowledge on their performance as GPFs is still limited. In this study, modeling on backpressure and filtration efficiency of fibrous media was carried out to determine the basic design criteria (filtration area, filter thickness and size) for different target efficiencies and backpressures at given gas flow conditions. Filter media with different fiber sizes (8 - 17 μm) and porosities (80% - 95%) were evaluated using modeling to determine the influence of fiber size and porosity.
Technical Paper

Cold Start Performance and Enhanced Thermal Durability of Vanadium SCR Catalysts

2009-04-20
2009-01-0625
For diesel applications, cold start accounts for a large amount of the total NOx emissions during a typical Federal Test Procedure (FTP) for light-duty vehicles and is a key focus for reducing NOx emissions. A common form of diesel NOx aftertreatment is selective catalytic reduction (SCR) technology. For cold start NOx 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 NOx performance and improved thermal durability. Three V-SCR technologies were tested for their thermal durability and low-temperature NOx 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.
Technical Paper

Influence of Hydrocarbon Storage on the Durability of SCR Catalysts

2008-04-14
2008-01-0767
Selective catalytic reduction (SCR) is a technology capable of meeting Tier 2 Bin 5 emissions levels of oxides of nitrogen (NOX) for diesel engines. Base metal zeolite catalysts show the best combination of thermal durability and NOX conversion activity. It is shown in this work that some base metal zeolite catalysts can store high levels of hydrocarbons (HCs). Also, base metal zeolite catalysts can catalyze oxidation of HCs under certain conditions. Oxidation of stored hydrocarbons can lead to permanent catalyst deactivation due to the exotherm generated in the SCR catalyst (over-temperature condition leading to SCR catalyst damage). This paper discusses a laboratory bench test to characterize hydrocarbon storage and burn-off characteristics of several SCR catalyst formulations, as well as engine dynamometer tests showing hydrocarbon storage and exotherm generation.
Technical Paper

Advanced Urea SCR System Study with a Light Duty Diesel Vehicle

2012-04-16
2012-01-0371
U.S. federal vehicle emission standards effective in 2007 require tight control of NOx and hydrocarbon emissions. For light-duty vehicles, the current standard of Tier 2 Bin 5 is about 0.07 g/mi NOx and 0.09 g/mi NMOG (non-methane organic gases) at 120,000 mi. However, the proposed future standard is 0.03 g/mi for NMOG + NOx (~SULEV30) at 150,000 mi. There is a significant improvement needed in catalyst system efficiencies for diesel vehicles to achieve the future standard, mainly during cold start. In this study, a less than 6000 lbs diesel truck equipped with an advanced urea Selective Catalytic Reduction (SCR) system was used to pursue lower tailpipe emissions with an emphasis on vehicle calibration and catalyst package. The calibration was tuned by optimizing exhaust gas recirculation (EGR) fuel injection and cold start strategy to generate desirable engine-out emissions balanced with reasonable temperatures.
Technical Paper

The Influence of Ammonia to NOX Ratio on SCR Performance

2007-04-16
2007-01-1581
It is likely that use of urea-based selective catalytic reduction (SCR) will be needed to meet U.S. Tier 2 diesel emission standards for oxides of nitrogen (NOx). The ideal ratio of ammonia (NH3) molecules to NOx molecules (known as alpha) is 1:1 based on urea consumption and having NH3 available for reaction of all of the exhaust NOx. However, SCR efficiency can be less than 100% at low temperatures in general, and at higher temperatures with high exhaust SCR catalyst space velocities. At the low temperatures where NOx conversion efficiency is low, it may be advantageous to reduce the alpha ratio to values less than one (less NH3 than is needed to convert 100% of the NOx emissions) to avoid NH3 slip. At higher space velocities and high temperatures, the NOx conversion efficiency may be higher with alpha ratios greater than 1. There is however concern that the additional NH3 will be slipped under these conditions.
Technical Paper

Laboratory and Engine Study of Urea-Related Deposits in Diesel Urea-SCR After-Treatment Systems

2007-04-16
2007-01-1582
Diesel exhaust systems equipped with selective catalytic reduction (SCR) catalysts based on urea were subjected to an aging process where the exhaust gas temperature was below 300°C. Solid deposits related to urea injection were found on the wall of the exhaust pipe down stream of the urea injector and on a urea mixer in front of the SCR catalyst. In laboratory tests, an aqueous solution of urea (1.5wt%) was dripped onto an SCR catalyst core in a simulated lean gas mixture at a rate corresponding to a 1:1 NH3-to-NOx ratio (NOx = 350ppm) and a space velocity (SV) of 15,000 h-1 at various temperatures. At 300°C and below, urea-related deposits appeared on the SCR catalyst surface and totally plugged the SCR catalyst monolith within 250 hours. When the aging temperature was 350°C or above, no deposits were observed on the SCR catalyst core.
Technical Paper

NOx Control Development with Urea SCR on a Diesel Passenger Car

2004-03-08
2004-01-1291
Diesel vehicles have significant advantages over their gasoline counterparts including a more efficient engine, higher fuel economy, and lower emissions of HC, CO, and CO2. However, NOx control is more difficult on a diesel because of the high O2 concentration in the exhaust, making conventional three-way catalysts ineffective. Two current available technologies for continuous NOx reduction onboard diesel vehicles are Selective Catalytic Reduction (SCR) using aqueous urea and lean NOx trap (LNT) catalysts. This paper discusses an application with SCR. SCR with ammonia has been used for many years at stationary sources. Aqueous urea is a convenient way to deliver ammonia onboard a vehicle and high NOx efficiencies have been shown in past work by Ford and others using urea. Tailpipe NOx emissions from a modified European production level 1.8L diesel Ford Focus TDCi were reduced to the range of ULEVII levels (0.05 g/mi NOx) with a green catalyst system.
Technical Paper

Technical Advantages of Urea SCR for Light-Duty and Heavy-Duty Diesel Vehicle Applications

2004-03-08
2004-01-1292
The 2007 emission standards for both light-duty and heavy-duty diesel vehicles remain a challenge. A level of about 90% NOx conversion is required to meet the standards. Technologies that have the most potential to achieve very high NOx conversion at low temperatures of diesel exhaust are lean NOx traps (LNTs) and Selective Catalytic Reduction (SCR) of NOx using aqueous urea, typically known as Urea SCR. The LNT has the advantage of requiring no new infrastructure, and does not pose any new customer compliance issues. However, Urea SCR has high and durable NOx conversion in a wider temperature window, a lower equivalent fuel penalty, and lower system cost. On a technical basis, Urea SCR has the best chance of meeting the 2007 NOx targets. This paper reviews the results of some demonstration programs for both light-and heavy-duty applications.
Technical Paper

Application of Urea SCR to Light-Duty Diesel Vehicles

2001-09-24
2001-01-3623
Diesel vehicles have significant advantages over their gasoline counterparts including a more efficient engine, higher fuel economy, and lower emissions of HC, CO, and CO2. However, NOx control is more difficult on a diesel because of the high O2 concentration in the exhaust, making conventional three-way catalysts ineffective. The most promising technology for continuous NOx reduction onboard diesel vehicles is Selective Catalytic Reduction (SCR) using aqueous urea. Recent work with urea SCR has involved aftertreatment for the 1.2L DIATA common-rail diesel engine. This engine was used in Ford's hybrid-electric vehicle, the Prodigy, which was developed under the PNGV (Partnership for a New Generation of Vehicles) program. An emission control system consisting of a diesel particulate filter followed by an underbody SCR system was used successfully to meet ULEV emission standards (0.2 g/mi NOx, 0.04 g/mi particulate matter (PM)).
Journal Article

The Development of Low Temperature Three-Way Catalysts for High Efficiency Gasoline Engines of the Future

2017-03-28
2017-01-0918
In anticipation that future gasoline engines will have improved fuel efficiency and therefore lower exhaust temperatures during low load operation, a project was initiated in 2014 to develop three-way catalysts (TWC) with improved activity at lower temperatures while maintaining the durability of current TWCs. This project is a collaboration between Ford Motor Company, Oak Ridge National Laboratory, and the University of Michigan and is funded by the U.S. Department of Energy. The ultimate goal is to show progress towards the USDRIVE goal of 90% conversion of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) at 150°C after high mileage aging. A reactor was set up at Ford to follow the catalyst testing protocols established by the USDRIVE ACEC tech team for evaluating catalysts for stoichiometric gasoline direct-injection (S-GDI) engines; this protocol specifies a stoichiometric blend of CO/H2, NO, C3H6, C2H4, C3H8, O2, H2O, and CO2 for the evaluations.
Journal Article

Combined Fe-Cu SCR Systems with Optimized Ammonia to NOx Ratio for Diesel NOx Control

2008-04-14
2008-01-1185
Selective catalytic reduction (SCR) is a viable option for control of oxides of nitrogen (NOx) from diesel engines. Currently, copper zeolite (Cu-zeolite) SCR catalysts are favored for configurations where the exhaust gas temperature is below 450°C for the majority of operating conditions, while iron zeolite (Fe-zeolite) SCR catalysts are preferred where NOx conversion is needed at temperatures above 450°C. The selection of Cu-zeolite or Fe-zeolite SCR catalysts is based on the different performance characteristics of these two catalyst types. Cu-zeolite catalysts are generally known for having efficient NOx reduction at low temperatures with little or no NO2, and they tend to selectively oxidize ammonia (NH3) to N2 at temperatures above 400°C, leading to poor NOx conversion at elevated temperatures.
Journal Article

The Effect of Hydrocarbons on the Selective Catalyzed Reduction of NOx over Low and High Temperature Catalyst Formulations

2008-04-14
2008-01-1030
Selective Catalytic Reduction of NOx is a promising technology to enable diesel engines to meet certification under Tier 2 Bin 5 emissions requirements. SCR catalysts for vehicle use are typically zeolitic materials known to store both hydrocarbons and ammonia. Ammonia storage on the zeolite has a beneficial effect on NOx conversion; hydrocarbons however, compete with ammonia for storage sites and may also block access to the interior of the zeolites where the bulk of the catalytic processes take place. This paper presents the results of laboratory studies utilizing surrogate hydrocarbon species to simulate engine-out exhaust over catalysts formulated to operate in both low (≈175-500°C) and high temperature (≈250-600°C) regimes. The effects of hydrocarbon exposure of these individual species on the SCR reaction are examined and observations are made as to necessary conditions for the recovery of SCR activity.
Technical Paper

Laboratory Postmortem Analysis of 120k mi Engine Aged Urea SCR Catalyst

2007-04-16
2007-01-1579
Selective Catalytic Reduction (SCR) of NOx with aqueous urea and a Catalyzed Diesel Particulate Filter (CDPF) has been considered as one of the emission control systems for diesel vehicles required to meet Federal Tier 2 and California LEVII emission standards. At Ford Motor Company, a DOC-SCR-CDPF system containing a copper / zeolite SCR catalyst was aged to 120k mi on the engine dynamometer using an aging cycle that mimicked both city and highway driving modes. A total of 643 CDPF regenerations occurred during the aging that raised the SCR catalyst to a temperature of up to 650°C on a regular basis. A series of lab analyses including activity tests, ammonia thermal desorption, BET surface area, XRF, XRD, and EPMA was conducted on cores taken from the 120k mi engine aged SCR catalyst brick. The lab post-mortem characterizations revealed the changes of catalyst properties, and the deterioration profile of the SCR catalyst brick after undergoing real aging conditions.
Journal Article

Sulfur Tolerance and DeSOx Studies on Diesel SCR Catalysts

2008-04-14
2008-01-1023
Base metal/zeolite catalysts, particularly containing copper and iron, are among the leading candidates for treatment of NOx emissions for diesel applications. Even with the use of ultra low sulfur fuel, sulfur poisoning is still a durability issue for base metal/zeolite SCR catalysts. In this study, the impact of sulfur poisoning on SCR activity and the stored sulfur removal effectiveness were investigated on several Cu and Fe/zeolite SCR catalysts after different thermal aging. The impact of sulfur was more significant on the Cu than on Fe/zeolite SCR catalysts for the NOx activity. It was found that the sensitivity of thermal aging status to the sulfur poisoning impact was different. The impact of sulfur on NOx activity changed with thermal aging on some catalysts, while it remained relatively the same for other catalysts. The most thermally durable SCR catalyst was not necessarily the most durable to sulfur poisoning.
Journal Article

Deactivation of Cu/Zeolite SCR Catalyst Due To Reductive Hydrothermal Aging

2008-04-14
2008-01-1021
Temperature programmed reduction by CO, H2, and propylene (C3H6), as well as hydrothermal aging in the presence of mixture of NO, HC, CO, H2 and O2 were used to study the deactivation of Cu/zeolite SCR catalysts. The presence of CO had no detrimental effect on catalyst activity. Carbonaceous deposit on the catalyst surface from propylene (C3H6) reduction suppressed the catalyst activity and burn off of carbonaceous deposit recovered activity, the presence of O2 suppressed carbonaceous deposit formation. The presence of H2 under lean conditions had much less effect on catalyst activity than H2 presence under rich conditions. Rich conditions with O2 presence represented the most detrimental effect on catalyst activity.
Journal Article

Technical Advantages of Vanadium SCR Systems for Diesel NOx Control in Emerging Markets

2008-04-14
2008-01-1029
Selective catalytic reduction (SCR) is a promising technology for diesel aftertreatment to meet NOx emissions targets in several countries. In established markets such as the US and Europe, zeolite SCR systems are expected to be used due to their ability to survive the exhaust gas temperatures seen in an active diesel particulate filter regeneration. In emerging markets where the fuel sulfur level may be as high as 2000 parts per million, zeolite SCR catalysts may have durability issues. In these markets, low sulfur fuel is needed overall to meet emissions standards and to avoid high sulfate emissions, but the aftertreatment system must be durable to high sulfur levels because there is a risk of exposure to high sulfur fuel. Also, emissions standards may be met without a DPF in some applications, so that the exhaust system would not see temperatures of 600°C or higher.
Technical Paper

The Development of Advanced Urea-SCR Systems for Tier 2 Bin 5 and Beyond Diesel Vehicles

2010-04-12
2010-01-1183
An advanced diesel aftertreatment system utilizing Selective Catalytic Reduction (SCR) with urea for lean nitrogen oxides (NOx) control was tested on a 2.7L V6 Land Rover vehicle to demonstrate the capability of achieving Tier 2 Bin 5 and lower emission standards for light-duty trucks. SCR washcoat was applied to a diesel particulate filter (DPF) to perform NOx and particulate reduction simultaneously. Advanced SCR systems employed both traditional SCR catalysts and SCR-coated filters (SCRF) to improve the NOx reduction efficiency. The engine-out NOx level was adjusted by modifying the EGR (Exhaust Gas Recirculation) calibration. Cold start NOx performance was improved by SCR warm-up strategy and urea over injection. This study showed the advanced SCR system could tolerate higher NH₃ storage in the SCR catalyst, resulting in overall higher NOx conversion on the FTP-75 test cycle.
Journal Article

Lubricant-Derived Ash Impact on Gasoline Particulate Filter Performance

2016-04-05
2016-01-0942
The increasing use of gasoline direct injection (GDI) engines coupled with the implementation of new particulate matter (PM) and particle number (PN) emissions regulations requires new emissions control strategies. Gasoline particulate filters (GPFs) present one approach to reduce particle emissions. Although primarily composed of combustible material which may be removed through oxidation, particle also contains incombustible components or ash. Over the service life of the filter the accumulation of ash causes an increase in exhaust backpressure, and limits the useful life of the GPF. This study utilized an accelerated aging system to generate elevated ash levels by injecting lubricant oil with the gasoline fuel into a burner system. GPFs were aged to a series of levels representing filter life up to 150,000 miles (240,000 km). The impact of ash on the filter pressure drop and on its sensitivity to soot accumulation was investigated at specific ash levels.
Journal Article

Rapidly Pulsed Reductants in Diesel NOx Reduction by Lean NOx Traps: Effects of Mixing Uniformity and Reductant Type

2016-04-05
2016-01-0956
Lean NOx Traps (LNTs) are one type of lean NOx reduction technology typically used in smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package . However, the performance of lean NOx traps (LNT) at temperatures above 400 C needs to be improved. The use of Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of a LNT in order to expand its operating window to higher temperatures and space velocities. This approach has also been called Di-Air (diesel NOx aftertreatment by adsorbed intermediate reductants) by Toyota. There is a vast parameter space which could be explored to maximize RPR performance and reduce the fuel penalty associated with injecting hydrocarbons. In this study, the mixing uniformity of the injected pulses, the type of reductant, and the concentration of pulsed reductant in the main flow were investigated.
Technical Paper

The Effects of SO2 and SO3 Poisoning on Cu/Zeolite SCR Catalysts

2009-04-20
2009-01-0898
Copper/zeolite catalysts are the leading urea SCR catalysts for NOx emission treatment in diesel applications. Sulfur poisoning directly impacts the overall SCR performance and is still a durability issue for Cu/zeolite SCR catalysts. Most studies on sulfur poisoning of Cu/zeolite SCR catalysts have been based on SO2 as the poisoning agent. It is important to investigate the relative poisoning effects of SO3, especially for systems with DOCs in front of Cu/zeolite SCR catalysts. It was observed that SCR activity was significantly reduced for samples poisoned by SO3 vs. those poisoned by SO2. The sulfur was released mainly as SO2 for both samples poisoned by SO2 and SO3. The temperatures and the magnitudes of released SO2 peaks however, were very different between the samples poisoned by SO2 vs. SO3. The results indicate that sulfur poisoning by SO2 and SO3 are not equivalent, with different poisoning mechanisms and impacts.
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