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Technical Paper

Durability of Low-Emissions Small Off-Road Engines

2004-09-27
2004-32-0058
The goal of the project was to reduce tailpipe-out hydrocarbon (HC) plus oxides of nitrogen (NOx) emissions to 50 percent or less of the current California Air Resources Board (CARB) useful life standard of 12 g/hp-hr for Class I engines, or 9 g/hp-hr for Class II engines. Low-emission engines were developed using three-way catalytic converters, passive secondary-air induction (SAI) systems, and in two cases, enleanment. Catalysts were integrated into the engine's mufflers, where feasible, to maintain a compact package. Due to the thermal sensitivity of these engines, carburetor calibrations were left unchanged in four of the six engines, at the stock rich settings. To enable HC oxidation under such rich conditions, a simple passive supplemental air injection system was developed. This system was then tuned to achieve the desired HC+NOx reduction.
Technical Paper

Catalytic Converter Design from Mat Material Coupon Fragility Data

2004-03-08
2004-01-1760
Automotive catalytic converters must provide a very high level of mechanical and thermal durability to maintain performance during their 100,000 to 150,000 mile life expectancy. The work reported herein characterizes the converter as a base (can) excited spring (mat material) supported mass (substrate). A mat material coupon test apparatus was developed for the purpose of providing parameter data for the converter model in the form of stiffness and material loss factor data as a function of shear deflection across the mat. An intumescent mat material was chosen and its dynamic properties evaluated for a range of converter operating parameters. The mat material response properties were placed into a mat material database as a function of gap bulk density, substrate temperature, and temperature gradient across the mat.
Technical Paper

Effect of Phased Air/Fuel Ratio Perturbation and Catalyst O2 Storage Capability on Catalyst Conversion Efficiency

2000-10-16
2000-01-2924
Recent internal research performed at SwRI examined an emissions control mechanism that we have labeled, ‘phased A/F perturbation.’ The suggested mechanism of phased perturbation involves independently controlling the fuel delivered to each bank of a dual bank engine, which allows the two banks to have an adjustable, relative A/F perturbation phase-shift from one another. Exhaust from the two banks can be combined to achieve a near-stoichiometric mixture prior to entering a single underbody catalyst. Since both rich and lean exhaust species would be present simultaneously, a highly reactive mixture would continuously enter the catalyst. In that work, it was found that A/F phasing produced as significant an effect on conversion efficiency as perturbation amplitude and frequency, i.e. A/F phasing was identified as a third dimension for optimization of exhaust gas composition as it enters the catalyst.
Technical Paper

On-Board Hydrogen Generation for Rapid Catalyst Light-Off

2000-06-19
2000-01-1841
This paper describes an on-vehicle demonstration of a hydrogen-heated catalyst (HHC) system for reducing the level of cold-start hydrocarbon emissions from a gasoline-fueled light-duty vehicle. The HHC system incorporated an onboard electrolyzer that generates and stores hydrogen (H2) during routine vehicle operation. Stored hydrogen and supplemental air are injected upstream of a platinum-containing automotive catalyst when the engine is started. Rapid heating of the catalytic converter occurs immediately as a result of catalytic oxidation of hydrogen (H2) with oxygen (O2) on the catalyst surface. Federal Test Procedure (FTP) emission results of the hydrogen-heated catalyst-equipped vehicle demonstrated reductions of hydrocarbons (HC) and carbon monoxide (CO) up to 68 and 62 percent, respectively. This study includes a brief analysis of the emissions and fuel economy effects of a 10-minute period of hydrogen generation during the FTP.
Technical Paper

Container Deformation Procedure for Ceramic Monolith Catalytic Converters

2000-03-06
2000-01-0217
A typical automotive catalytic converter is constructed with a ceramic substrate and a steel shell. Due to a mismatch in coefficients of thermal expansion, the steel shell will expand away from the ceramic substrate at high temperatures. The gap between the substrate and shell is usually filled with a fiber composite material referred to as “mat.” Mat materials are compressed during assembly and must maintain an adequate pressure around the substrate under extreme temperature conditions. The container deformation measurement procedure is used to determine catalytic converter shell expansion during and after a period of hot catalytic converter operation. This procedure is useful in determining the potential physical durability of a catalytic converter system, and involves measuring converter shell expansion as a function of inlet temperature. A post-test dimensional measurement is used to determine permanent container deformation.
Technical Paper

Catalytic Converter Mat Material Durability Measurement Under Controlled Thermal and Vibration Environments

2000-03-06
2000-01-0221
To aid in the catalytic converter design and development process, a test apparatus was designed and built which will allow comparative evaluation of the durability of candidate mat materials under highly controlled thermal and vibration environments. The apparatus directly controls relative shear deflection between the substrate and can to impose known levels of mat material strain while recording the transmitted shear force across the mat material. Substrate and can temperatures are controlled at constant levels using a resistive thermal exposure (RTE) technique. Mat material fatigue after several million cycles is evident by a substantial decrease in the transmitted force. A fragility test was found to be an excellent method to quickly compare candidate materials to be used for a specific application. Examples of test results from several materials are given to show the utility of the mat material evaluation technique.
Technical Paper

Catalytic Converter Vibration Measurement Under Dynamometer Simulated Roadloads

2000-03-06
2000-01-0029
In order to further reduce vehicle cold-start emissions, the use of catalytic converters that are “close-coupled” to the exhaust manifold is increasing. To understand the vibrational environment of close-coupled and underbody converters, a laboratory study was conducted on several passenger vehicles. Catalytic converter vibration spectra were measured on a chassis dynamometer with the vehicle operating over a variety of test conditions. Vehicle operating conditions included hard accelerations and extended steady-state speeds at distinct throttle positions over zero-percent and four-percent simulated road grades.
Technical Paper

Catalytic Converter Thermal Environment Measurement Under Dynamometer Simulated Roadloads

2000-03-06
2000-01-0216
An increasing number of passenger vehicle exhaust systems incorporate catalytic converters that are “close-coupled” to the exhaust manifold to further reduce the quantity of cold-start emissions and increase overall catalyst conversion efficiencies. In general, close-coupled catalytic converters are not necessarily subjected to higher inlet exhaust temperatures than conventional underbody catalytic converters. To establish a foundation of on-vehicle temperature data, several passenger vehicles with close-coupled catalytic converters were studied while operating on a chassis dynamometer. Converter temperatures were measured over a variety of vehicle test conditions, including accelerations and extended steady-state speeds for several throttle positions, at both zero- and four-percent simulated road grades.
Technical Paper

Effects of Catalyst Formulation on Vehicle Emissions With Respect to Gasoline Fuel Sulfur Level

1999-10-25
1999-01-3675
Proposed emissions standards will require that emissions control systems function at extremely high efficiency. Recently, studies have shown that elevated gasoline fuel sulfur levels (GFSL) can impair catalytic converter efficiency. In this study, a variety of tri-metal catalysts were evaluated to determine if formulation changes could reduce emissions sensitivity to GFSL. Catalysts with elemental composition similar to an OEM, but with double the precious metal (PM) loading, were evaluated using 38 and 620 ppm GFSL. Doubling the PM loading significantly reduced catalyst sensitivity to sulfur. Doubling the rhodium loading, at the expense of the platinum loading, significantly improved NOx emission sulfur sensitivity.
Technical Paper

A Comparison of Emissions and Flow Restriction of Thinwall Ceramic Substrates for Low Emission Vehicles

1999-03-01
1999-01-0271
The emission and flow restriction characteristics of three different ceramic substrates with varying wall thickness and cell density (400 cpsi/6.5 mil, 600/4.3, and 600/3.5) are compared. These 106mm diameter substrates were catalyzed with similar amounts of washcoat and fabricated into catalytic converters having a total volume of 2.0 liters. A Pd/Rh catalyst technology was applied at a concentration of 6.65 g/l and a ratio of 20/1. Three sets of converters (two of each type) were aged for 100 hours on an engine dynamometer stand. After aging, the FTP performance of these converters were evaluated on an auto-driver FTP stand using a 2.4L, four-cylinder prototype engine and on a 2.4L, four-cylinder prototype vehicle. A third set of unaged converters was used for cold flow restriction measurements and vehicle acceleration tests.
Technical Paper

Reduced Cold-Start Emissions Using Rapid Exhaust Port Oxidation (REPO) in a Spark-Ignition Engine

1997-02-24
970264
An emissions reduction strategy was developed and demonstrated to significantly reduce cold-start hydrocarbon (HC) and CO emissions from a spark ignition (SI), gasoline-fueled engine. This strategy involved cold-starting the engine with an ultra-fuel rich calibration, while metering near-stoichiometric fractions of air directly into the exhaust ports. Using this approach, exhaust constituents spontaneously ignited at the exhaust ports and burned into the exhaust manifold and exhaust pipe leading to the catalytic converter. The resulting exotherm accelerated catalyst heating and significantly decreased light-off time following a cold-start on the FTP-75 with a Ford Escort equipped with a 1.9L engine. Mass emissions measurements acquired during the first 70 seconds of the FTP-75 revealed total-HC and CO reductions of 68 and 50 percent, respectively, when compared to baseline measurements.
Technical Paper

EHC Impact on Extended Hot Soak Periods

1995-10-01
952418
Emission performance of a late model vehicle equipped with an electrically-heated catalytic converter (EHC) system was evaluated after extended vehicle soak periods that ranged from 30 to 180 minutes. As soak periods lengthened, NMHC and CO emissions measured in hot transient driving cycles increased by 125 percent and 345 percent, respectively. These tests were baseline operations which had no resistance heating or secondary air injection to the converter system. Sources of increased NMHC and CO emissions as a function of vehicle soak time were both the converter system cool-down characteristics and engine restart calibration strategy. For soak periods of 30 and 60 minutes, EHC resistance heating without secondary air injection resulted in large improvements in NMHC and CO emission performance (i.e., 74 percent and 54 percent lower NMHC emissions versus no heat, no air operation after a 30- and 60-minute period, respectively).
Technical Paper

Effects of Cetane Number, Aromatics, and Oxygenates on Emissions From a 1994 Heavy-Duty Diesel Engine With Exhaust Catalyst

1995-02-01
950250
A Coordinating Research Council sponsored test program was conducted to determine the effects of diesel fuel properties on emissions from two heavy-duty diesel engines designed to meet EPA emission requirements for 1994. Results for a prototype 1994 DDC Series 60 were reported in SAE Paper 941020. This paper reports the results from a prototype 1994 Navistar DTA-466 engine equipped with an exhaust catalyst. A set of ten fuels having specific variations in cetane number, aromatics, and oxygen were used to study effects of these fuel properties on emissions. Using glycol diether compounds as an oxygenated additive, selected diesel fuels were treated to obtain 2 and 4 mass percent oxygen. Cetane number was increased for selected fuels using a cetane improver. Emissions were measured during transient FTP operation of the Navistar engine tuned for a nominal 5 g/hp-hr NOx, then repeated using a 4 g/hp-hr NOx calibration.
Technical Paper

Natural Gas Converter Performance and Durability

1993-03-01
930222
Natural gas-fueled vehicles impose unique requirements on exhaust aftertreatment systems. Methane conversion, which is very difficult for conventional automotive catalysts, may be required, depending on future regulatory directions. Three-way converter operating windows for simultaneous conversion of HC, CO, and NOx are considerably more narrow with gas engine exhaust. While several studies have demonstrated acceptable fresh converter performance, aged performance remains a concern. This paper presents the results of a durability study of eight catalytic converters specifically developed for natural gas engines. The converters were aged for 300 hours on a natural gas-fueled 7.0L Chevrolet engine operated at net stoichiometry. Catalyst performance was evaluated using both air/fuel traverse engine tests and FTP vehicle tests. Durability cycle severity and a comparison of results for engine and vehicle tests are discussed.
Technical Paper

Design and Development of Catalytic Converters for Diesels

1992-09-01
921677
Improvements in diesel engine design to reduce particulate emissions levels, and a recent Environmental Protection Agency (EPA) ruling limiting the maximum sulfur content in diesel fuel, enhanced the viability of catalytic aftertreatment for this market. The Department of Emissions Research, Southwest Research Institute (SwRI), under contract from the Engine Manufacturers Association, (EMA), conducted a search to identify flow-through catalyst technologies available to reduce particulate emissions without trapping. The search revealed a variety of catalyst formulations, washcoats, and substrate designs which were screened on a light-duty diesel. Based on the performance of eighteen converters evaluated, several designs were selected to continue experimentation on a modern technology heavy-duty diesel engine.
Technical Paper

Cold-Start Hydrocarbon Collection for Advanced Exhaust Emission Control

1992-02-01
920847
This paper describes the findings of a laboratory effort to demonstrate improved automotive exhaust emission control with a cold-start hydrocarbon collection system. The emission control strategy developed in this study incorporated a zeolite molecular sieve in the exhaust system to collect cold-start hydrocarbons for subsequent release to an active catalytic converter. A prototype emission control system was designed and tested on a gasoline-fueled vehicle. Continuous raw exhaust emission measurements upstream and downstream of the zeolite molecular sieve revealed collection, storage, and release of cold-start hydrocarbons. Federal Test Procedure (FTP) emission results show a 35 percent reduction in hydrocarbons emitted during the cold-transient segment (Bag 1) due to adsorption by the zeolite.
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