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Technical Paper

Palladium and Platinum/Rhodium Dual-Catalyst NLEV and Tier IIa Close-Coupled Emission Solutions

2001-03-05
2001-01-0923
Dual-monolith converters containing Pd-only catalysts followed by Pt/Rh three-way catalysts (TWCs) provide effective emission solutions for NLEV and Tier IIa close-coupled dual-bank V-8 applications due to optimal hydrocarbon and NOx light-off, transient NOx control, and balance of precious metal (PGM) usage. Dual-catalyst [Pd +Pt/Rh] systems on a 5.3L V-8 LEV light truck vehicle were characterized as a function of PGM loading, catalyst technology, and substrate cell density. NLEV hydrocarbon emission control of the 6500 lb vehicle was optimal using dual 1.2L converters with each containing front ceria-free Pd catalysts coupled with rear Pt/Rh TWCs. Advanced non-air prototype calibrations coupled with reduced catalyst washcoat mass on 600cpsi/4mil substrate resulted in minimal Pd usage of ∼0.02 toz/vehicle due to achieving catalyst inlet temperatures of 350-400°C in <10 sec on both banks of the V-8 engine.
Technical Paper

Measurement of Flame Front Structure and Its Thickness by Planar and Local Chemiluminescence of OH*, CH* and C2*

2001-03-05
2001-01-0920
We have measured the local flame front structure and its thickness using high speed three CCD camera and Developed Cassegrain optics, which could measure local OH*, CH* and C2* radicals at a point. The time-series OH*, CH* and C2* planar images are compared to those measured by local radical. The results show that the CH* and C2* signals can be a nice marker of flame front structure and its thickness, while OH* has some uncertainty.
Technical Paper

Application of Advanced Three-Way Catalyst Technologies on High Cell Density Ultra Thin-Wall Ceramic Substrates for Future Emission Legislations

2001-03-05
2001-01-0924
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.
Technical Paper

Study of Modern Application Strategies for Catalytic Aftertreatment Demonstrated on a Production V6 Engine

2001-03-05
2001-01-0925
A study was performed to develop optimum design strategies for a production V6 engine to maximize catalyst performance at minimum pressure loss and at minimum cost. Test results for an advanced system, designed to meet future emission limits on a production V6 vehicle, are presented based on FTP testing. The on-line pressure loss and temperature data serves to explain the functioning of the catalyst.
Technical Paper

Improving Combustion Process by Using a High Speed UV-Sensitive Camera

2001-03-05
2001-01-0917
The ever increasing demands on combustion engines with regard to exhaust emissions and fuel consumption require the use of modern analytical methods. Especially optical measurement techniques have contributed a lot to the realization of complicated engine concepts. The disadvantages of complex measurement techniques are the expenditure of time and the necessary changes of the engine. This paper introduces a new practice oriented optical measurement technique with the aid of an example. With this technique it is possible to record the combustion process with a sampling rate of up to 200 kHz through a small drilling. Even quick events like knocking can be recorded. The combustion luminosity is watched through a special UV-capable borescope, transmitted to an array of photoelectric transformers and finally recorded as a flame figure. We will show an SI-engine which is limited by knocking.
Technical Paper

Quantification of Fuel Concentrations and Estimation of Liquid/Vapor Ratios in Direct Injection Gasoline Sprays by Laser-Induced Fluorescence

2001-03-05
2001-01-0916
Gasoline direct-injection sprays are studied in a pressurized vessel with the help of optical diagnostic techniques. Exciplex laser-induced fluorescence images show that the liquid phase is located on the edges of the spray induced recirculation zone, while the vapor is contained within this zone. These trends are particularly pronounced with a low ambient pressure (0.12 MPa), and a short injection duration. A new method is proposed to calculate the global evaporated fuel fraction of the spray. In typical iso-octane sprays, the evaporated fuel is less than 50 % at 6 ms after start of injection, for an ambient temperature of 75°C. A low boiling point fuel - n-pentane - is used to model the behavior at high temperatures, which enhances evaporation. Quantified fuel/air ratio images are obtained using laser-induced fluorescence of acetone. The accuracy is poor if high liquid concentrations exist. The fuel/air ratio often exceeds 5 in large zones.
Technical Paper

Local A/F Measurement by Chemiluminescence OH*, CH* and C2* in SI Engine

2001-03-05
2001-01-0919
The chemiluminescence emission intensity can be measured with high temporal resolution, leading to understanding the chemical reaction. Time-series chemiluminescence measurements of OH*, CH* and C2* were carried out to understand flame propagation speed, its thickness and A/F ratio of combustion status. The optical piston head (quartz) allows us to visualize combustion chamber. It is found that the chemiluminescence intensity ratio of CH*/OH* and C2*/OH* can estimate local A/F. The A/F measured by O2 sensor was used for evaluation and the results indicate this method can be applicable to estimate A/F.
Technical Paper

Measurement of the Flame Lift-Off Location on DI Diesel Sprays Using OH Chemiluminescence

2001-03-05
2001-01-0918
The flame on a high injection pressure direct-injection (DI) diesel spray under quiescent conditions stabilizes at a location downstream of the fuel injector. The distance from the injector to the location of stabilization is referred to as the flame “lift-off” length (or height). Air entrained into a diesel spray upstream of the flame lift-off length will mix with the injected fuel. The air and fuel premixed upstream of the lift-off length are believed to react immediately downstream of the location of flame lift-off. Recent measurements suggest that as much as 20% of the air required to burn the fuel injected is entrained prior to the flame lift-off length for typical, moderate-load, heavy-duty DI diesel conditions. These results imply that combustion at the flame lift-off location will play a pivotal role in diesel combustion and emission formation processes.
Technical Paper

Prediction of Catalytic Performance during Light-off Phase with Different Wall Thickness, Cell Density and Cell Shape

2001-03-05
2001-01-0930
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.
Technical Paper

Monolithic Metal Oxide Thin-Wall Substrates with Closed and Open Cells: Optimal Designs by Theoretical Modeling and Experiment

2001-03-05
2001-01-0931
Recently, ASMT has developed a process of making monolithic metal oxide thin-wall structures from mechanically assembled metal preforms, whose shape and internal configuration are retained in the (oxidation) process. Because metallic designs can be extremely diverse, the same varieties of designs are now possible in metal oxide ceramics. In particular, some unique metallic designs such as spiral winding structures (formed from flat and corrugated layers) with either closed or open cells have been realized for the first time in ceramics, such as hematite Fe2O3 and titania (rutile) TiO2. In order to optimize these new ceramic designs, we have developed a theoretical model of layer distribution of mechanical stresses under external uniform radial pressure and of thermal stresses under typical heating/cooling regimes.
Technical Paper

Modeling the Effect of Substrate Cell Shape on Conversion in Monolith Catalysts

2001-03-05
2001-01-0932
Mass transfer limitations from the bulk gas phase to the surface of the catalyst as well as mass transfer limitations within the washcoat itself have important effects on conversion in washcoated monolith catalysts. These factors depend upon the shape of the channel as well as the loading of washcoat material. This paper outlines a method to describe the washcoat distribution profile for different channel shapes and washcoat loadings. This allows for prediction of effectiveness factors and bulk mass transfer coefficients as a function of cell geometry and washcoat loading for the oxidation of propane. It was found that differences in the diffusion limitations within the washcoat control conversion in the catalyst more than differences in bulk mass transfer rates when comparing different cell shapes. The results show that optimum washcoat loadings exist for the geometry of each cell, and that these optimum loadings are a function of catalyst temperature.
Technical Paper

New Catalyst Preparation Procedure for OBDII-Monitoring Requirements

2001-03-05
2001-01-0933
In order to match catalyst OBDII conditions the common procedure is oven aging with air, which is not suitable for complete converter systems due to mantle corrosion. The goal was, therefore, to find an alternative procedure to ensure a defined catalyst aging that would match 1,75 times the emission standard and is also good for SULEV. The new procedure currently being developed allows the aging of metal and ceramic catalysts as well as complete catalyst systems. The paper will present the aging process, emission data of fresh and aged catalysts and the feedback to the test car OBDII system.
Technical Paper

A Comparison of Conversion Efficiency and Flow Restriction Performance of Ceramic and Metallic Catalyst Substrates

2001-03-05
2001-01-0926
Catalyst systems utilizing ceramic and metallic substrates were compared to assess the influence of various substrate parameters on the exhaust gas conversion efficiency and flow restriction. In particular, the substrate surface area, substrate specific heat capacity, and substrate volume were all evaluated for their importance in estimating the conversion efficiency of the catalyst system. Additionally, substrate open frontal area and cell hydraulic diameter were compared against exhaust restriction performance.
Technical Paper

Investigation on a Novel Reactor Design for Emission Control Catalysts -Modeling and Experimental Results-

2001-03-05
2001-01-0928
It is well known that the catalytic efficiency and durability of an automotive catalytic converter can be significantly affected by its design. This paper demonstrates the potential for further improvement in both the durability and efficiency by using a novel catalytic converter concept based on a large frontal area, high cell density substrate. This concept requires that attention be paid to optimization of the flow as well as of the mounting system. The converter design is determined with a computational fluid dynamic (CFD) simulation and the effect of this design on the temperature distribution in the substrate is calculated and measured. Due to this novel converter concept the maximum substrate temperature is reduced, which results in a better aging behavior. This improvement allows a reduction in precious metal content without a loss in efficiency.
Technical Paper

Application Guideline to Define Catalyst Layout for Maximum Catalytic Efficiency

2001-03-05
2001-01-0929
The influence of physical parameters of the catalyst's substrate such as thermal mass, hydraulic diameter and geometric surface area on catalyst's efficiency is well known as published in numerous works. This paper will show interactions of these parameters and will provide a guideline on how to design the optimum system for a specific application, taking into account system's back pressure and system costs. Based on engine test bench results that show the influence of the physical parameters, the results for the optimized design regarding emission tests and maximum conversion rate at higher loads will be demonstrated.
Technical Paper

1D Unsteady Flows with Chemical Reactions in the Exhaust Duct-System of S.I. Engines: Predictions and Experiments

2001-03-05
2001-01-0939
This paper describes some recent advances of the research work concerning the 1D fluid dynamic modeling of unsteady reacting flows in s.i. engine pipe-systems, including pre-catalysts and main catalysts. The numerical model GASDYN developed in previous work has been further enhanced to enable the simulation of the catalyst. The main chemical reactions occurring in the wash-coat have been accounted in the model, considering the mass transfer between gas and solid phase. The oxidation of CO, C3H6, C3H8, H2 and reduction of NO, the steam-reforming reactions of C3H6, C3H8, the water-gas shift reaction of CO have been considered. Moreover, an oxygen-storage sub-model has been introduced, to account for the behavior of Cerium oxides. A detailed thermal model of the converter takes into account the heat released by the exothermic reactions as a source term in the heat transfer equations. The influence of the insulating mat is accounted.
Technical Paper

A Modular Numerical Simulation Tool Predicting Catalytic Converter Light-Off by Improved Modeling of Thermal Management and Conversion Characteristics

2001-03-05
2001-01-0940
Strict legislation standards for automotive emission limits (e.g. ULEV, SULEV), which target for HC conversion rates beyond 99 %, impose the necessity to dramatically shorten catalyst Light-Off time and increase catalytic efficiency through improved catalytic converter heat-up. Especially, in early design stages, modeling thermal energy management is crucial to predict wether emissions standards can be met. The CAE method (Computer Aided Engineering) presented in this study gives the flexibility composing the frontal exhaust system from modular numerical models, which describe heat transfer in single exhaust components, as e.g. takedown-pipes, flexible coupling element (FCE), flanges and conversion characteristics in catalytic converter. Each module upstream of the converter internally couples the energy equations of 1Dgas to 1D/2D-solid-structure, including heat transfer mechanism as radiation, natural and forced convection.
Technical Paper

The Solution for Steady State Temperature Distribution in Monolithic Catalytic Converters

2001-03-05
2001-01-0941
This paper presents a simplified thermal model for round catalytic converters in steady state operation. Using this model, the analytic solution for the temperature distribution in the monolithic substrate is obtained. This analytic solution in the substrate is, then, combined with those in the intumescent mat [1] and the metal shell to obtain the temperature profile in the radial direction of the converter except for three unknown temperatures at the three material interfaces, which can be solved using an Excel application program. This analytical temperature solution facilitates the studies of the effects of various design parameters such as the exhaust gas temperature, exhaust gas flow rate, substrate cell geometry, converter dimensions, and ambient temperature and flow, etc.
Technical Paper

Optimum Gap Design And Durability Analysis of Catalytic Converter Assembly

2001-03-05
2001-01-0942
A method to predict gap distribution, can deformation and mounting force of catalytic converter during assembling and operation cycles has been developed using ABAQUS contact algorithm with user subroutine for material properties. Inherent in the methodology is the constitutive model for both vermiculite mat and wire mesh mounting materials, which is able to describe their nonlinear and thermal behaviors and shows good agreement with test results. A design optimization procedure is presented to achieve uniform gap design of can and substrate. The technology will enable engineers to generate robust converter can designs, substrate shape and stamping tools for minimum manufacturing failure rate and maximum durability performance once a mounting material is selected.
Technical Paper

Shear Strength of Cordierite Ceramic Catalyst Supports

2001-03-05
2001-01-0935
An analytical model for estimating shear and bending stresses during canning of cordierite ceramic catalyst supports is presented. These stresses arise when the radial pressure distribution is nonuniform due, primarily, to variations in gap bulk density (GBD ) of intumescent mat around the perimeter of the substrate. Variations in GBD can occur during canning, regardless of the canning technique, due to anisotropic can stiffness or component tolerances or mat overlap. The model helps relate shear and bending stresses to substrate size and orientation, elastic modulii, cell size and wall porosity. If these stresses approach the corresponding strength of substrate, a shear crack may develop during or after the canning process depending on the magnitude of stress. A special test fixture was developed to measure the shear strength of ceramic catalyst supports, with different cell sizes, before and after the application of washcoat.
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