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Technical Paper

High Temperature Stability of Ceria-Zirconia Supported Pd Model Catalysts

1998-02-23
980668
A series of ceria and ceria-zirconia supported Pd model automotive catalysts were prepared and aged under air or redox conditions at 1050°C for 12 h. The supports were manufactured by different methods and represent a range of compositions. The samples were characterized before and after aging by BET, X-ray diffraction, mercury porosimetry, XPS, H2 temperature-programmed reduction, and oxygen storage capacity measurements. Oxygen storage measurements revealed that the behavior of the catalysts varied according to aging conditions and temperature of measurement. Pd/ceria-zirconia catalysts showed higher oxygen storage characteristics after 1050°C aging than Pd/ceria catalysts, and the phase purity of the ceria-zirconia was shown to positively affect the amount of oxygen storage. The initial rates of oxygen release from the model catalysts at 350°C were shown to depend on the preparation conditions of the supports.
Technical Paper

Closed-Loop Air-Fuel Ratio Control Using Forced Air-Fuel Ratio Modulation

1998-02-23
980041
An air-to-fuel ratio (A/F) modulation scheme is presented in which a linear feedback signal is generated from a heated exhaust gas oxygen (EGO) sensor. In this scheme, the engine A/F is modulated with a triangular waveform, and the mean value of the EGO output is obtained using a rolling average filter. The resulting output is linearly related to the exhaust A/F, and is used to provide closed-loop lean A/F operation following a cold start to enhance catalyst light-off and minimize vehicle exhaust emissions. Some engine-dynamometer results obtained using the method are presented.
Technical Paper

A View of Flexible Fuel Vehicle Aldehyde Emissions

1988-08-01
881200
The aldehyde emissions of 1.6L and 5.0L flexible fuel vehicles (FFV) have been measured, with and without a catalyst, on a range of fuels. The “zero mile” catalyzed emission levels of formaldehyde when operating on M85 (85% methanol and 15% gasoline) are in the 5-15 mg/mi range, but as mileage accumulates they tend to be in the 30-50 mg/mi range. The feedgas levels are high and appear to correlate with engine displacement. The formaldehyde and methanol emissions are higher when operating on M100, compared to M85, but the non-oxygenated hydrocarbon emissions are about the same for both fuels, which suggests that the use of M85 may actually provide more air quality benefit than M100. High mileage control of aldehydes to the level of gasoline vehicles does not appear possible with current technology.
Technical Paper

50,000 Mile Vehicle Road Test of Three-Way and NOx Reduction Catalyst Systems

1978-02-01
780608
The performance of three way and NOx catalysts was evaluated on vehicles utilizing non-feedback fuel control and electronic feedback fuel control. The vehicles accumulated 80,450 km (50,000 miles) using fuels representing the extremes in hydrogen-carbon ratio available for commercial use. Feedback carburetion compared to non-feedback carburetion improved highway fuel economy by about 0.4 km/l (1 mpg) and reduced deterioration of NOx with mileage accumulation. NOx emissions were higher with the low H/C fuel in the three way catalyst system; feedback reduced the fuel effect on NOx in these cars by improving conversion efficiency with the low H/C fuel. Feedback had no measureable effect on HC and CO catalyst efficiency. Hydrocarbon emissions were lower with the low H/C fuel in all cars. Unleaded gasoline octane improver, MMT, at 0.015g Mn/l (0.06 g/gal) increased tailpipe hydrocarbon emissions by 0.05 g/km (0.08 g/mile).
Technical Paper

Evaluation of Three-Way Catalysts - Part III Formation of NH3, Its Suppression by SO2 and Re-Oxidation

1978-02-01
780606
This is the third and final communication in this series of laboratory evaluation of three-way catalysts. The effect of inlet NO concentration and temperature on the NH3 formation over fresh, pulsator-aged and dynamometer-aged three-way catalysts of the current generation has been investigated under temperatures and exhaust compositions of practical interest. In spite of differences in aging procedures employed, both the pulsator and dynamometer-aged catalysts show similar selectivity behavior. The effect of SO2 in feed-gas on gross NO conversion and NH3 formation was studied over Pt-Rh and Pt-Rh-Ru types of three-way catalysts. A strong dependence of the gross NO conversion on the SO2 concentration in exhaust gas mixtures was noted. A simultaneous suppression of gross NO conversion and NH3 formation, in presence of SO2 in feed-gas, is attributed to the poisoning of Pt sites on aged three-way catalysts.
Technical Paper

Virtual Exhaust Gas Temperature Measurement

2017-03-28
2017-01-1065
Exhaust temperature models are widely used in the automotive industry to estimate catalyst and exhaust gas temperatures and to protect the catalyst and other vehicle hardware against over-temperature conditions. Modeled exhaust temperatures rely on air, fuel, and spark measurements to make their estimate. Errors in any of these measurements can have a large impact on the accuracy of the model. Furthermore, air-fuel imbalances, air leaks, engine coolant temperature (ECT) or air charge temperature (ACT) inaccuracies, or any unforeseen source of heat entering the exhaust may have a large impact on the accuracy of the modeled estimate. Modern universal exhaust gas oxygen (UEGO) sensors have heaters with controllers to precisely regulate the oxygen sensing element temperature. These controllers are duty cycle based and supply more or less current to the heating element depending on the temperature of the surrounding exhaust gas.
Technical Paper

Three-Way Catalyst Diagnostics and Prognostics Based on Support Vector Machines

2017-03-28
2017-01-0975
A three-way catalytic converter (TWC) is an emissions control device, used to treat the exhaust gases in a gasoline engine. The conversion efficiency of the catalyst, however, drops with age or customer usage and needs to be monitored on-line to meet the on board diagnostics (OBD II) regulations. In this work, a non-intrusive catalyst monitor is developed to diagnose the track the remaining useful life of the catalyst based on measured in-vehicle signals. Using air mass and the air-fuel ratio (A/F) at the front (upstream) and rear (downstream) of the catalyst, the catalyst oxygen storage capacity is estimated. The catalyst capacity and operating exhaust temperature are used as an input features for developing a Support Vector Machine (SVM) algorithm based classifier to identify a threshold catalyst. In addition, the distance of the data points in hyperspace from the calibrated threshold plane is used to compute the remaining useful life left.
Technical Paper

Evolution of Engine Air Induction System Hydrocarbon Traps

2017-03-28
2017-01-1014
Engine air induction systems hydrocarbon trap (HC trap) designs to limit evaporative fuel emissions, have evolved over time. This paper discusses a range of HC traps that have evolved in engine air induction systems. (AIS) The early zeolite flow through HC trap utilized an exhaust catalyst technology internal stainless steel furnace brazed substrate coated with zeolite media. This HC trap was installed in the AIS clean air tube. This design was heavy, complicated, and expensive but met the urgency of the implementation of the new evaporative emissions regulation. The latest Ford Motor Company HC trap is a simple plastic tray containing activated carbon with breathable non-woven polyester cover. This design has been made common across multiple vehicle lines with planned production annual volume in the millions. The cost of the latest HC trap bypass design is approximately 5% of the original stainless steel zeolite flow through HC trap.
Technical Paper

DEVELOPMENT AND EVALUATION OF AUTOMOBILE EXHAUST CATALYTIC CONVERTER SYSTEMS

1962-01-01
620397
For the past seven years, the Ford Motor Company has been working on the development of catalytic exhaust treating systems designed to minimize the emission of certain vehicle exhaust gas constituents. In 1959, the development of a low-temperature, catalytic-converter system for the oxidation of exhaust gas hydrocarbons was described in a paper presented to the SAE. That system, which used vanadium pentoxide as the catalyst, has since been extensively developed in a program that included 250,000 miles of converter evaluation on vehicles. Many of the basic system requirements and problems covered in those tests are relevant in vehicle applications of a catalytic converter system with any type of catalyst. With the insertion of a carbon monoxide limit in the California Exhaust Standard, work on the low-temperature, catalytic converter system was discontinued since this system did not, and was not designed to, oxidize carbon monoxide.
Technical Paper

Laboratory Study to Determine Impact of Na and K Exposure on the Durability of DOC and SCR Catalyst Formulations

2009-11-02
2009-01-2823
A laboratory flow reactor study was utilized to determine the durability impact of alkali metal (Na and K) exposure on three Pt/Pd-based diesel oxidation catalysts (DOC), two vanadium-based selective catalytic reduction (SCR) catalysts, and two Cu/zeolite-based SCR catalysts. All catalyst samples were contaminated by direct deposition of Na or K by an incipient wetness technique. The activity impact on the contaminated DOCs was accomplished by evaluating for changes in CO and HC light-off. The activity impact on the contaminated SCR catalysts was accomplished by evaluating for changes in the Standard SCR Reaction, the Fast SCR Reaction, the Ammonia Oxidation Reaction, and the Ammonia Storage Capacity. Contamination levels of 3.0 wt% Na was found to have a higher negative impact on Pt-based and zeolite containing DOCs for T-50 CO and HC light-off.
Technical Paper

Cold Start Performance and Enhanced Thermal Durability of Vanadium SCR Catalysts

2009-04-20
2009-01-0625
For diesel applications, cold start accounts for a large amount of the total NOx emissions during a typical Federal Test Procedure (FTP) for light-duty vehicles and is a key focus for reducing NOx emissions. A common form of diesel NOx aftertreatment is selective catalytic reduction (SCR) technology. For cold start NOx improvement, the SCR catalyst would be best located as the first catalyst in the aftertreatment system; however, engine-out hydrocarbons and no diesel oxidation catalyst (DOC) upstream to generate an exotherm for desulfation can result in degraded SCR catalyst performance. Recent advances in vanadia-based SCR (V-SCR) catalyst technology have shown better low temperature NOx performance and improved thermal durability. Three V-SCR technologies were tested for their thermal durability and low-temperature NOx performance, and after 600°C aging, one technology showed low-temperature performance on par with state-of-the-art copper-zeolite SCR (Cu-SCR) technology.
Technical Paper

Experimental and Modeling Study of a Diesel Oxidation Catalyst (DOC) under Transient and CPF Active Regeneration Conditions

2013-04-08
2013-01-1046
In this study, a DOC catalyst was experimentally studied in an engine test cell with a2010 Cummins 6.7L ISB diesel and a production aftertreatment system. The test matrix consisted of steady state, active regeneration with in-cylinder fuel dosing and transient conditions. Conversion efficiencies of total hydrocarbon (THC), CO, and NO were quantified under each condition. A previously developed high-fidelity DOC model capable of predicting both steady state and transient active regeneration gaseous emissions was calibrated to the experimental data. The model consists of a single 1D channel where mass and energy balance equations were solved for both surface and bulk gas regions. The steady-state data were used to identify the activation energies and pre-exponential factors for CO, NO and HC oxidation, while the steady-state active regeneration data were used to identify the inhibition factors. The transient data were used to simulate the thermal response of the DOC.
Technical Paper

LNT+SCR Catalyst Systems Optimized for NOx Conversion on Diesel Applications

2011-04-12
2011-01-0305
A laboratory study was performed to assess the effectiveness of LNT+SCR systems for NOx control in lean exhaust. The effects of the catalyst system length and the spatial configuration of the LNT & SCR catalysts were evaluated for their effects on the NOx conversion, NH₃ yield, N₂O yield, and HC conversion. It was found that multi-zone catalyst architectures with four or eight alternating LNT and SCR catalyst zones had equivalent gross NOx conversion, lower NH₃ and N₂O yield, and significantly higher net conversion of NOx to N₂ than an all-LNT design or a standard LNT+SCR configuration, where all of the SCR volume is placed downstream of the LNT. The lower NH₃ emissions of the two multi-zone designs relative to the standard LNT+SCR design were attributed to the improved balance of NOx and NH₃ in the SCR zones.
Technical Paper

Development of Emission Transfer Functions for Predicting the Deterioration of a Cu-Zeolite SCR Catalyst

2009-04-20
2009-01-1282
Urea selective catalytic reduction (SCR) catalysts have the capability to deliver the high NOx conversion efficiencies required for future emission standards. However, the potential for the occasional over-temperature can lead to the irreversible deactivation of the SCR catalyst. On-board diagnostics (OBD) compliance requires monitoring of the SCR function to make sure it is operating properly. Initially, SCR catalyst performance metrics such as NOx conversion, NH3 oxidation, NH3 storage capacity, and BET surface area are within normal limits. However, these features degrade with high temperature aging. In this work, a laboratory flow reactor was utilized to determine the impact on these performance metrics as a function of aging condition. Upon the completion of a full time-at-temperature durability study, four performance criteria were established to help determine a likely SCR failure.
Technical Paper

A Simplified Method to Make Temperature Measurements of a Metal Surface using the Surface as One Component of Thermocouple

2008-04-14
2008-01-0918
Instrumentation of an exhaust system to measure surface temperature at multiple locations usually involves welding independent thermocouples to the surface of the system. This report describes a new type of thermocouple fabricated to measure temperature at a point or temperature difference between points on a metallic object utilizing the metal as one component of the new thermocouple. AISI 316 stainless steel is used in the current study to represent automotive exhaust pipe. The other component of the thermocouple is Nickel-Chromium (Chromel, Chromega), one of the two metals used in type K thermocouples, which are generally used for exhaust temperature measurements during emission tests. Use of the new thermocouple is contingent upon an accurate calibration of its response to changes in temperature.
Technical Paper

Adequacy of Reduced Order Models for Model-Based Control in a Urea-SCR Aftertreatment System

2008-04-14
2008-01-0617
Model-based control strategies are important for meeting the dual objective of maximizing NOx reduction and minimizing NH3 slip in urea-SCR catalysts. To be implementable on the vehicle, the models should capture the essential behavior of the system, while not being computationally intensive. This paper discusses the adequacy of two different reduced order SCR catalyst models and compares their performance with a higher order model. The higher order model assumes that the catalyst has both diffusion and reaction kinetics, whereas the reduced order models contain only reaction kinetics. After describing each model, its parameter identification and model validation based on experiments on a Navistar I6 7.6L engine are presented. The adequacy of reduced order models is demonstrated by comparing the NO, NO2 and NH3 concentrations predicted by the models to their concentrations from the test data.
Technical Paper

Influence of Hydrocarbon Storage on the Durability of SCR Catalysts

2008-04-14
2008-01-0767
Selective catalytic reduction (SCR) is a technology capable of meeting Tier 2 Bin 5 emissions levels of oxides of nitrogen (NOX) for diesel engines. Base metal zeolite catalysts show the best combination of thermal durability and NOX conversion activity. It is shown in this work that some base metal zeolite catalysts can store high levels of hydrocarbons (HCs). Also, base metal zeolite catalysts can catalyze oxidation of HCs under certain conditions. Oxidation of stored hydrocarbons can lead to permanent catalyst deactivation due to the exotherm generated in the SCR catalyst (over-temperature condition leading to SCR catalyst damage). This paper discusses a laboratory bench test to characterize hydrocarbon storage and burn-off characteristics of several SCR catalyst formulations, as well as engine dynamometer tests showing hydrocarbon storage and exotherm generation.
Technical Paper

Opportunities for Brazilian OBD in the Context of I/M

2008-10-07
2008-36-0168
This paper presents a comprehensive overview of Brazilian On-Board Diagnostic (OBD) regulations, Inspection and Maintenance (I/M) Programs and Aftermarket Catalyst regulations as well as an overview of similar regulations in the United States and Europe. Opportunities and technical risks are described in this context. Regulatory information contained in this Paper is intended to serve as reference only. Updated and complete rules and regulations must be used for official purposes. The implementation of the second stage of Brazilian OBD (OBDBr-2), starting in 2010, represents a significant improvement towards exhaust emission control and on-board diagnostic monitoring. Its effectiveness and credibility will be heavily influenced by how this new technology is integrated into I/M programs and how well it meshes with aftermarket catalyst regulations. Currently, Brazilian I/M regulations do not incorporate any OBD requirements and only Rio de Janeiro State has implemented an I/M Program.
Technical Paper

Catalyst Performance Evaluation on E0 and E85 Fuels

2011-04-12
2011-01-0904
The differences in hydrocarbons (HCs) emitted by gasoline (E0) and ethanol (EtOH) blend fuels from flex-fuel capable engines can lead to differences in the performance of aftertreatment devices. Vehicle emission results have shown either better performance on E0 compared to E85 or vice versa, dependent on the vehicle calibration. In order to separate the impact of the vehicle and the catalyst, a laboratory study was conducted to evaluate performance on a pulse-flame (pulsator) reactor and compare reactivity towards E0 and E85 (85% EtOH-15% E0) exhaust. The catalysts evaluated were substrate-only, washcoat-only and fully formulated catalysts that had been aged either on a pulsator reactor or dynamometer engine. Catalyst performance was evaluated with light-off tests utilizing both slow and fast temperature ramp rates.
Technical Paper

Exhaust System Thermal Management: A Process to Optimize Exhaust Enthalpy for Cold Start Emissions Reduction

2017-03-28
2017-01-0141
Future vehicle North American emissions standards (e.g., North American Tier 3 Bin 30 or LEVIII SULEV 30) require the exhaust catalyst to be greater than 80% efficient by 20 seconds after the engine has been started in the Federal Test Procedure. Turbocharged engines are especially challenged to deliver fast catalyst light-off since the presence of the turbocharger in the exhaust flow path significantly increases exhaust system heat losses. A solution to delivering cost effective SULEV 30 emissions in turbocharged engines is to achieve fast catalyst light-off by reducing exhaust system heat losses in cold start, without increasing catalyst thermal degradation during high load operation. A CAE methodology to assess the thermal performance of exhaust system hardware options, from the exhaust port to the catalyst brick face is described, which enables compliance with future emissions regulations.
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