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High cell density (HCD) (≥ 600 cpsi) and /or ultra thin wall (UTW) (≤ 4 mil) extruded ceramic monolith substrates are being used in many new automotive catalyst applications because they offer (1) increased geometric surface area, (2) lower thermal mass, (3) increased open frontal area and (4) higher heat and mass transfer rates. Delphi has shown in previous papers how to use the effectiveness, NTU theory, to optimize the various benefits of these HCD / UTW catalysts. A primary disadvantage of these low solid fraction substrates is their reduced structural strength, as measured by a 3-D hydrostatic (isostatic) test. The weakest of these new substrates is only 10 to 20% as strong as standard 400 × 6.5 substrates. Improved converter assembly methods with lower, more uniform forces will likely be required to successfully assemble converters with such weak substrates in production.

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.

Radioisotopic methods have been applied to nondestructive measurements on experimental automotive catalytic converters. These converters consist of thin corrugated metal foil which supports an alumina coating impregnated with noble metals. A radiogauging system, using γ radiation from a gadolinium-153 source, was developed to determine the total quantity and distribution of alumina coating applied to the foil substrate. The radiogauging apparatus was also used to provide axial and radial profiles of lead deposited in the catalytic converter when leaded fuel was used. During dynamometer aging, iron-59 was used as a radiotracer in the alumina to monitor the coating attrition as a function of operating time. These studies demonstrate the capability of radiotracer and radiogauging techniques for rapid, nondestructive measurements on prototype catalytic converters during performance testing.

A test apparatus containing two raw-gas particulate sampling systems was designed and developed to determine accurately the performance of various materials as diesel exhaust particulate filters. This apparatus was used in conjunction with a single-cylinder diesel engine and a series of fibrous filters to quantify experimentally the effects of filter face area, filter thickness, packing density and fiber diameter on filter performance. Time-dependent efficiency measurements made with this system were smooth and consistent for all of the filters tested and correctly reflected the changes made in these key trap parameters. In all cases, the collection efficiency of the filters increased during the first hour of operation and then reached a relatively constant level. The pressure drop across the filters increased continuously as particulate material accumulated on the filters.

A mathematical model has been developed to describe the initial performance of fibrous filters for diesel exhaust particulates. In addition to the basic mechanisms of particle deposition on fibers, the size distributions of both diesel particulates and fibers were incorporated into the model in order to account for the polydispersity of particles and fibers encountered in realistic diesel particulate filters. Filtration experiments with a single-cylinder diesel engine were conducted to test the validity of the model, and the calculated filter efficiencies agreed very well with the experimental data.