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Technical Paper

Catalyzed Soot Filters in Close Coupled Position for Passenger Vehicles

Recently, catalyzed soot filters (CSF) for passenger vehicles have been introduced into the marketplace to comply with the European environmental requirements and future emission standards. The initial system consisted of one or two diesel oxidation catalysts (DOC) to meet the regulated HC and CO standards along with an under floor CSF to treat the particulate emissions. In order to meet the cold start requirements and to reduce system costs with a CSF only unit, converters are placed closer to the engine to minimize heat losses and more of the DOC functionality is integrated into the filter substrate. This work describes the development of such DOC-integrated CSF systems. One major challenge in the design of such systems is to ensure that there is sufficient catalyst functionality within the wall-flow substrate while maintaining an acceptable exhaust gas backpressure across the filter.
Technical Paper

Influence of Phosphorous Poisoning on TWC Catalysts

Gasoline engine oils contain a variety of additives including phosphorous-based compounds, for maintaining their characteristics. During the life of the vehicle, oil is consumed via piston ring blowby or leakage from valve stem guides. Phosphorous compounds from the consumed oil end up being deposited on the three way conversion catalysts resulting in a degradation of the conversion efficiencies of all three pollutants, hydrocarbons, carbon monoxide and nitrogen oxides. To simulate this deterioration in performance, an accelerated aging cycle has been developed which replicates the effect of the interaction between the phosphorous species and the washcoat components. This paper describes the poison aging protocol and the effect of aging temperature, poison level and duration of aging. In this paper, we will we also discuss some of the catalyst deactivation mechanisms and methods to simulate them using dynamometer-mounted engines.
Technical Paper

Sulfur Management of NOx Adsorber Technology for Diesel Light-duty Vehicle and Truck Applications

Sulfur poisoning from engine fuel and lube is one of the most recognizable degradation mechanisms of a NOx adsorber catalyst system for diesel emission reduction. Even with the availability of 15 ppm sulfur diesel fuel, NOx adsorber will be deactivated without an effective sulfur management. Two general pathways are currently being explored for sulfur management: (1) the use of a disposable SOx trap that can be replaced or rejuvenated offline periodically, and (2) the use of diesel fuel injection in the exhaust and high temperature de-sulfation approach to remove the sulfur poisons to recover the NOx trapping efficiency. The major concern of the de-sulfation process is the many prolonged high temperature rich cycles that catalyst will encounter during its useful life. It is shown that NOx adsorber catalyst suffers some loss of its trapping capacity upon high temperature lean-rich exposure.
Technical Paper

Emissions Implications of a Twin Close Coupled Catalyst System Designed for Improved Engine Performance on an In-line 4 Cylinder Engine

The emission capability of an exhaust system tuned for improved engine performance from an in-line four-cylinder engine has been investigated. The exhaust system comprises two close-coupled catalysts; each located in separate exhaust streams and has been termed the 4-2 close-coupled catalysts (CCC) -1 system. It has been shown that, given equivalent total catalyst volume, this system configuration results in compromised high exhaust flow rate emissions performance compared with a single catalyst (4-1semi-CCC) system. This emissions performance deficit has been attributed to the effect of engine frequency flow pulsations, which result in relatively high peak space velocities in the 4-2CCC-1 system despite the mean space velocity being consistent. Engine-based AFR Bias Sweep tests suggest that hydrocarbon emissions are most strongly affected by this phenomenon. At lower exhaust flow rates, the difference in performance between the two systems is negligible.
Technical Paper

A Study of Lean NOx Technology for Diesel Emission Control

The aim of this paper is to investigate the potential of Lean NOx technology for diesel emission control. In this work, the focus is on the precious metal (low temperature) catalyst. Engelhard optimized the catalyst for cells per square inch (cpsi) and Platinum loading. Effect of various parameters, including, reductant type, catalyst volume, space velocity range and injector locations were investigated both analytically and experimentally at Cummins in search for the optimum system design. Both steady state and transient tests were conducted in this work. The precious metal catalysts have a narrow temperature window, however, with the use of proper reductant and an efficient control strategy (to minimize fuel penalty) cycle conversion efficiencies as high as 40% may be obtained for FTP-75. The analysis tool developed to aid the system design is capable of predicting effects of catalyst temperature, NOx concentration, O2 concentration, space velocity etc. on NOx conversion efficiency.
Technical Paper

Engine Dynamometer and Vehicle Performance of a Urea SCR-System for Heavy-Duty Truck Engines

The application of SCR deNOx aftertreatment was studied on two about 12 liter class heavy-duty diesel engines within a consortium project. Basically, the system consists of a dosage system for aqueous urea injection and a vanadia based SCR catalyst, without an upstream or downstream oxidation catalyst. The urea injection system for a DAF and a Renault V.I. (Véhicules Industriels) diesel engine was calibrated on the engine test bench taking into account dynamic effects of the catalyst. For both engine applications NOx reduction was 81% to 84% over the ESC and 72% over the ETC. CO emission increased up to 27%. PM emission is reduced by 4 to 23% and HC emission is reduced by more than 80%. These results are achieved with standard diesel fuel with about 350 ppm sulfur. The test engines and SCR deNOx systems were built into a DAF FT95 truck and a Renault V.I. Magnum truck.
Technical Paper

Pushing the Envelope to Near-Zero Emissions on Light-duty Gasoline Vehicles

The integration of advanced emission control technologies including advanced three-way catalysts and advanced, high cell density, ultra-thin wall substrates with advanced gasoline powertrains and advanced engine controls is necessary to achieve near-zero tailpipe emission requirements like California's SULEV or PZEV light-duty certification categories. The first gasoline vehicles meeting these near-zero regulations have been introduced in California in 2001. Advanced three-way catalysts targeted for these near-zero regulations feature layered architectures, thermally stable oxygen storage components, and segregated precious metal impregnation strategies. Engine calibration strategies focused on tight stoichiometric air/fuel control and fast catalyst heat-up immediately after engine start are important enablers to achieve near-zero hydrocarbon and NOx emissions.
Technical Paper

PremAir® Catalyst System – A New Approach to Cleaning the Air

Classical approaches to pollution control have been to develop benign, non-polluting processes or to abate emissions at the tailpipe or stack before release to the atmosphere. A new technology called PremAir® Catalyst Systems1 takes a different approach and reduces ambient, ground level ozone directly. This technology takes advantage of the huge volumes of air which are processed daily by both mobile and stationary heat exchange devices. For mobile applications, the new system involves placing a catalytic coating on a vehicle's radiator or air conditioning condenser. For stationary applications, the catalytic coating typically is applied to an insert, which is attached to the air conditioning condenser. In either case, the catalyst converts ozone to oxygen as ozone containing ambient air passes over the coated radiator or condenser surfaces.
Technical Paper

PremAir® Catalyst System

Traditional approaches to pollution control have been to develop benign non-polluting processes or to abate emissions at the tailpipe or stack before emitting to the atmosphere. A new technology called PremAir®* Catalyst Systems takes a different approach and directly reduces ambient ground level ozone. This technology can be applied to both mobile and stationary applications. For automotive applications, the new system involves placing a catalytic coating on the car's radiator or air conditioner condenser. As air passes over the radiator or condenser, the catalyst converts the ozone into oxygen. Three Volvo vehicles with a catalyst coating on the radiator were tested on the road during the 1997 summer ozone season in southern California to assess performance. Studies were also conducted in Volvo's laboratory to determine the effect of the catalyst coating on the radiator's performance with regard to corrosion, heat transfer and pressure drop.
Technical Paper

Plasma-Assisted Catalytic Reduction of NOx

Many studies suggest that lean-NOx SCR proceeds via oxidation of NO to NO2 by oxygen, followed by the reaction of the NO2 with hydrocarbons. On catalysts that are not very effective in catalyzing the equilibration of NO+O2 and NO2, the rate of N2 formation is substantially higher when the input NOx is NO2 instead of NO. The apparent bifunctional mechanism in the SCR of NOx has prompted the use of mechanically mixed catalyst components, in which one component is used to accelerate the oxidation of NO to NO2, and another component catalyzes the reaction between NO2 and the hydrocarbon. Catalysts that previously were regarded as inactive for NOx reduction could therefore become efficient when mixed with an oxidation catalyst. Preconverting NO to NO2 opens the opportunity for a wider range of SCR catalysts and perhaps improves the durability of these catalysts. This paper describes the use of a non-thermal plasma as an efficient means for selective partial oxidation of NO to NO2.
Technical Paper

A 45% Engine Size Catalyst System for MDV2 ULEV Applications

A catalyst system, consisting of two different catalyst technologies within a single canister, was developed for MDV2 (Medium-Duty Vehicles, Class 2) to meet ULEV targets. The catalyst volume versus engine displacement is less than 50%. Three approaches taken: substrate study, PM loading study and new catalyst technology development are illustrated here. The most promising system features new catalyst technologies coated on high cell density substrates.
Technical Paper

Catalytic Converter Development for Motorcycle Emission Control

Catalytic control of motorcycle vehicle emissions requires that the catalytic element be carefully integrated into the exhaust system. The catalyst element physical parameters are optimized to achieve specific exhaust tuning requirements. Since the converter is located inside the muffler, the peak temperatures can severely stress both the catalytic active washcoat materials and the currently used metal monolith structure under some operating conditions. This paper addresses the development of an alternative ceramic monolithic catalyst that can be used for 2 and 4-stroke motorcycle applications. A new mounting technique was developed to contain the ceramic catalytic unit within a holder or converter shell with sufficient strength and durability to withstand the severe environment of 2-stroke engine exhaust.
Technical Paper

The Development of a Close Coupled Plus Underfloor Catalyst for a ULEV Application

A close coupled plus underfloor catalyst system was developed for achieving the ULEV performance targets. Catalyst technologies of various precious metal combinations, as well as substrates of different cell densities and wall thicknesses were investigated. Catalyst systems with relatively high precious metal loadings were required to achieved the ULEV targets after simulated engine aging. High Pd-based three way catalysts (TWC), including trimetal and Pd/Pt catalysts together with substrates of low thermal mass, were demonstrated as the appropriate selections for the close coupled position. Pt/Rh and trimetal catalysts combined with substrates of high cell density, were shown to be the promising candidates for the underfloor position.
Technical Paper

Save the Diesel Fueled Engine: A Clean Diesel Engine with Catalytic Aftertreatment - The Alternative to Alternate Fuels

Off-Highway diesel engines may benefit from exhaust emission control systems developed for on-highway vehicles. Both the diesel oxidation catalyst and the catalytic soot filter are being used to remove diesel smoke and odor. The advantages of both of these technologies are explained. NOx emissions control from diesel engines are now being addressed. Alternate fuels, such as methanol or natural gas, have been designed to replace diesel fuel as a measure to control NOx emissions. To avoid transfer to alternate fuels and permit continued use of diesel fuel in diesel engines, two approaches are being studied. These are the use of exhaust gas recirculation (EGR) and the development of a new technology called a lean NOx reduction catalyst. EGR, if successfully developed, probably will require the use of a catalytic soot filter. Lean NOx catalysts have been developed but still are not at a practical stage yet.
Technical Paper

Effects of Sulfur on Performance of Catalytic Aftertreatment Devices

In the effort to design reliable diesel engines which meet the strict US Federal Regulations for emissions, considerable progress has been made by engine manufacturers. Particulate emissions are now below 0.25 g/BHPh and after 1994 will be below 0.1 g/BHPh. Diesel fuel has a revised specification limit of 0.05% sulfur as a means to assist diesel engine manufacturers in complying with the 1994 standard. Diesel oxidation catalysts (DOC) have been chosen as another means. A DOC can efficiently oxidize soluble organic particulate matter (SOF) and gaseous hydrocarbons while easily oxidizing SO2 to SO3-the latter being a particulate and undesirable. Selective DOCs have been developed which maintain the activity for SOF and minimize the undesirable SO2 oxidation step. However, performance for gaseous hydrocarbons may be negatively affected.