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Ceramic honeycomb wall flow diesel particulate filters (DPF) have been investigated for use in exhaust gas control of diesel vehicles. However, before they can be used, prevention of thermal shock failure during combustion regeneration is necessary. Studies were conducted on thermal shock failures on 9-inch diameter large volume DPF during regeneration by finite element analyses (FEA). These studies reveal that, within safe limits, maximum thermal stress is almost constant even at different gas flow rates and oxygen concentrations. Regeneration tests were also conducted on large volume DPF of several materials having different pore size distributions. FEA thermal stress was compared with mechanical strength of the material at safe levels.

Further stringent emission legislation requires advanced technologies, such as sophisticated engine management and advanced catalyst and substrate to achieve high catalytic performance, especially during the light-off phase. This paper presents the results of calculations and measurements of hydrocarbon and carbon monoxide light-off performance for substrates of different wall thickness, cell density and cell shapes. The experimental data from catalyst light-off testing on an engine dynamometer are compared with theoretical results of computer modeling under different temperature ramps and flow rates. The reaction kinetics in the computer modeling are derived from the best fit for the performance of conventional ceramic substrate (6mil/400cpsi), by comparing the theoretical and experimental results on both HC and CO emissions. The calibrated computer model predicts the effects of different wall thickness, cell density and cell shape.

The future emission limits for gasoline fuelled passenger cars require more and more efficient exhaust gas aftertreatment devices - the catalytic converter being one essential part of the complex system design. The present paper summarizes the results of several basic research programs putting major emphasis on the application of highly sophisticated three-way catalyst technologies being taylored for the utilization on ultra thin-wall ceramic substrates. In the first part of the investigation the following effects were examined in detail: Different washcoat loadings at constant PGM-loadings Different volumes of catalysts for constant amounts of PGM and washcoat Similar washcoat technologies at different ratios of WC-loading to precious metal concentration in the washcoat.

As emissions regulations are becoming more stringent, various efforts to improve emission performance have been carried out in different areas including the honeycomb structure of catalytic converters. This report describes the development of a simulation tool to predict emission performance and simulation results for different cell structures. The simulation model was developed based on global kinetic chemical reaction model [1]. Having tuned the reaction parameters through a light-off test and estimated oxygen storage capacity through an oxygen storage test, we ultimately tuned the model in a vehicle test (with Bags 1 and 2, FTP 75). As a result, the simulated cumulative tailpipe emissions are within ±25 percent of the test results. Parameter analyses indicate that the amount of emissions decreased as the density of cells increased and that the amount of emissions also decreased the thinner the wall thicknesses were.

Application of ceramic honeycomb wall-flow type diesel particulate filters (DPF) to heavy duty vehicles requires a large volume filter. Heavy duty vehicles produce a large volume exhaust gas, and pressure drop in the exhaust system must be maintained to a certain level. In addition, the filters must be designed to resist fracture from thermal stresses during regeneration. This is particularly important in heavy duty vehicles because of these extended mileage requirements. These studies of the effects of DPF volume on thermal shock resistance during regeneration reveal that the maximum failure temperatures are lower as DPF volume is increased, still maintaining 950°C maximum temperature with 12 ℓ volume and 9″D × 12″L size large DPF. Some thermal stress analyses with temperature profiles and finite element analysis were conducted on four different volume DPF during regeneration.

New ultra-low vehicle emission legislation requires advanced catalyst systems to achieve high conversion requirements. Manufacturers have to improve both the washcoat formulations and the catalyst substrate technology to meet these new regulations. This paper will present the results of a computer modeling study on the effects of ultra-thinwall catalysts on hydrocarbon and carbon monoxide light-off performance improvement. The experimental data from catalyst light-off testing on an engine dynamometer are compared with theoretical results of advanced substrate modeling for ultra-thin wall ceramic substrates. Results show that thermal mass has the greatest effect on light-off performance. Decreases in wall thickness offer the greatest benefit to light-off performance by lowering the thermal mass of the substrate, thus allowing it to reach light-off temperature faster.

Thermal shock performance parameters to assure Ultra Thin Wall (UTW) substrate durability for close-coupled (CC) converter operating conditions have been defined through testing and FEM modeling. Propane burner tests simulating the engine exhaust conditions were performed and coordinated with FEM stress analysis. For the stress analysis, a newly developed Macro-Micro Thermal Stress Analysis method was employed. Validation of the Macro-Micro Thermal Stress Analysis method was made through comparing FEM analysis results with the electric furnace and the burner tests results. A thermal fatigue life prediction method taking into account variation in material strength, fatigue degradation and effective volume was developed. In the verification tests, crack generation stresses were predicted within a 20 % margin of error.