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This paper includes a numerical and experimental study of fluid flow in automotive catalytic converters. The numerical work involves using computational fluid dynamics (CFD) to perform three-dimensional calculations of turbulent flow in an inlet pipe, inlet cone, catalyst substrate (porous medium), outlet cone, and outlet pipe. The experimental work includes using hot-wire anemometry to measure the velocity profile at the outlet of the catalyst substrate, and pressure drop measurements across the system. Very often, the designer may have to resort to offset inlet and outlet cones, or angled inlet pipes due to space limitations. Hence, it is very difficult to achieve a good flow distribution at the inlet cross section of the catalyst substrate. Therefore, it is important to study the effect of the geometry of the catalytic converter on flow uniformity in the substrate.

FTP emissions from a 2.2L four cylinder vehicle are measured from six different converters. These converters have been designed to have both similar flow restriction and to have similar platinum group metals. The durability of these six converters is evaluated after dynamometer aging of both 125 and 250 hours of RATsm aging. These catalytic converters use various combinations of 400/3.5 (400 cells/in2/3.5mil wall), 400/4.5, 400/6.5, 600/3.5, 600/4.5, and 900/2.5 ceramic substrates in order to meet a restriction target and to maximize converter geometric surface area. Total catalyst volume of the converters varies from 1.9 to 0.82 liters. Catalyst frontal area varies from 68 cm2 to 88 cm2. Five of the six converters use two catalyst bricks. The front catalyst brick uses either a three-way Pd washcoat technology containing ceria or a non-ceria Pd washcoat technology. To minimize dependence on palladium the rear brick uses a Pt/Rh washcoat at a loading of 0.06 Toz and a ratio of 5/0/1.

Advances in extrusion die technology allow ceramic substrate suppliers to provide new monolithic automotive substrates with considerably higher cell densities and thinner wall thicknesses. These new substrates offer both faster light off and better steady state efficiencies providing new flexibility in the design of automotive catalytic converters. The effectiveness-NTU methodology is used to evaluate various design parameters of the HCD substrates. Various theoretical derivations are supported with experimental results on substrates with cell densities ranging from 400 to 1200 cells per square inch with varying wall thicknesses. Performance effects such as steady state conversion, transient response both thermal and emission, flow restriction and FTP emissions results are evaluated. Poison deposition is studied and the effects on emissions performance evaluated.

This paper describes the experience gained during the successful development of a catalytic converter design for an in-line 4 cylinder application to meet the India 1998 cold start emissions standards. The vehicle application considered was an open loop carburetted system that met the 1997 hot start emission standards using a conventional Pt/Rh underbody mounted catalyst. The challenge was to meet the 1998 standards through catalyst changes and/or minor carburettor adjustments, thus providing the customer with the most cost-effective solution. The approach adopted was to use a mathematical computer simulation (MAESTRO™) developed by Delphi, that utilized engine out data obtained from emission testing of the vehicle to simulate proposed solutions. The biggest advantage of this approach was the ability to estimate the impact of system level changes on emissions performance thus enabling a quick optimization of the design variables.

A new adsorber system for reducing cold start HC emissions has been developed that offers a passive and simplified alternative to previous HC adsorber technologies. The series flow in-line adsorber concept combines existing catalyst technology with a zeolite based HC adsorber by simply incorporating one additional adsorber catalyst substrate into conventional catalytic converters without any valving, purging lines or special substrates. The HC adsorber catalyst consist of a durable zeolite, a washcoat binder, precious group metals and rare earth promoters on standard monolithic substrates. For selected vehicle applications, a single converter containing a light off catalyst, a catalyzed HC adsorber and a standard three-way catalyst can be used in the underfloor position. Even after severe engine aging, the vehicle FTP results show that this new technology remains effective in reducing the cold start HC emissions while providing good CO and NOx conversions.

A real world aging study was performed on a distributed converter system to investigate ULEV potential and aging aspects. Two V-6 vehicles were fitted with 0.7 Liter Pd close mounted catalysts on each exhaust manifold and a traditional 2.8 Liter three-way underfloor catalyst. These vehicles were then driven in a high mileage fleet while tracking emission results every 10K miles up to 50K miles. At the end of 50K miles the system met ULEV requirements for CO and NOx but NMHC exceeded the target. Verification of aging was done by chemically cleaning the close coupled catalyst and by comparison to a dynamometer aged set. The results showed that most of the degradation in NMHC performance was due to poisoning with little effect from thermal aging. With most of the CO and NOx abatement being done in the underfloor catalyst their degradation is mainly thermal.