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Technical Paper

Research Application of DFSS: Study of the Impact of Accelerated Aging and Recovery on Low-Rh Three-Way Catalyst Activity for Catalyst Monitoring

Robust on-board diagnosis of emission catalyst performance requires the development of artificially damaged "threshold" catalysts that accurately mimic the performance of damaged catalysts in customer use. The threshold catalysts are used by emissions calibrators to determine fore-aft exhaust oxygen sensor responses that indicate catalyst failure. Rather than rely on traditional trial-and-error processes to generate threshold catalysts, we have used a DFSS (Design For Six-Sigma) approach that explores, at a research level, the relationship between oxygen storage capacity (OSC) of the catalyst (i.e., the fundamental property dictating the response of the aft oxygen sensor) and key process input variables: high-temperature exposure, phosphorus poisoning, and catalyst "recovery."
Journal Article

Development of the Combustion System for a Flexible Fuel Turbocharged Direct Injection Engine

Gasoline turbocharged direct injection (GTDI) engines, such as EcoBoost™ from Ford, are becoming established as a high value technology solution to improve passenger car and light truck fuel economy. Due to their high specific performance and excellent low-speed torque, improved fuel economy can be realized due to downsizing and downspeeding without sacrificing performance and driveability while meeting the most stringent future emissions standards with an inexpensive three-way catalyst. A logical and synergistic extension of the EcoBoost™ strategy is the use of E85 (approximately 85% ethanol and 15% gasoline) for knock mitigation. Direct injection of E85 is very effective in suppressing knock due to ethanol's high heat of vaporization - which increases the charge cooling benefit of direct injection - and inherently high octane rating. As a result, higher boost levels can be achieved while maintaining optimal combustion phasing giving high thermal efficiency.
Technical Paper

Characterization of Phosphates Found in Vehicle-Aged Exhaust Gas Catalysts: A Raman Study

Phosphorus contamination from engine oil additives has been associated with reduced performance of vehicle-aged exhaust gas catalysts. Identifying phosphorus species on aged catalysts is important for understanding the reasons for catalytic performance degradation. However, phosphorus is present only in small quantities, which makes its detection with bulk analytical techniques difficult. Raman microscopy probes small regions (a few microns in diameter) of a sample, and can detect both crystalline and amorphous materials. It is thus ideal for characterizing phosphates that may have limited distribution in a catalyst. However, suitable Raman spectra for mixed-metal phosphates that might be expected to be present in contaminated catalysts are not generally available.
Journal Article

Three-Way Catalyst Light-off During the NEDC Test Cycle: Fully Coupled 0D/1D Simulation of Gasoline Combustion, Pollutant Formation and Aftertreatment Systems

The introduction of more stringent standards for engine emissions requires a steady development of engine control strategies in combination with efforts to optimize in-cylinder combustion and exhaust gas aftertreatment. With the goal of optimizing the overall emission performance this study presents the comprehensive simulation approach of a virtual vehicle model. A well established 1D gas dynamics and engine simulation model is extended by four key features. These are models for combustion and pollutant production in the cylinder, a model for the conversion of pollutants in a catalyst and a model for the effect of manifold wall wetting and fuel evaporation. The general species transport feature is linking these model together as it allows to transport an arbitrary number of chemical species in the entire system. Finally this highly detailed engine model is integrated into a vehicle model.
Technical Paper

Lean NOx Trap Desulfation Through Rapid Air Fuel Modulation

A novel method of desulfating lean NOx traps has been developed. Rapid, large amplitude modulation of the air to fuel ratio creates an exotherm of approximately 300°C in the LNT. AFR modulation results in oxidant and reductant breakthough in a three-way catalyst mounted upstream of the LNT. During lean modulation, oxygen is stored in the LNT. During rich modulation, the reductant reacts catalytically with the stored oxygen in the LNT, generating a substantial exotherm. Rich and lean AFR events are selected commensurate with the number of cylinders in the engine, resulting in each cylinder having exactly the same AFR history. This permits a deterministic programming of spark advance and precise coordination of spark advance with the transient fueling effect. The spark advance is retarded for the rich events and increases stepwise for groups of lean events. This strategy results in minimal disturbances in the engine imep.
Technical Paper

Three-Way Catalyst Performance Characterization

A simplified method was developed to obtain three-way catalyst performance data to be used for predicting vehicle CVS-H emissions. This method involves engine dynamometer aging of catalysts and characterization of their performance as a function of four variables, namely, redox potential, temperature, space velocity and a modulation parameter. In the process of reducing the number of variables, several simplifications were made. The simplifications, their limitations and the characteristic trends in the performance of a 11 Pt/Rh catalyst are discussed.
Technical Paper

A Simplified Approach to Modeling Exhaust System Emissions: SIMTWC

The optimized design of an exhaust emission system in terms of performance, cost, packaging, and engine control strategy will be a key part of competitively meeting future more stringent emission standards. Extensive use of vehicle experiments to evaluate design system tradeoffs is far too time consuming and expensive. Imperative to successfully meeting the challenges of future emission regulations and cost constraints is the development of an exhaust system simulation model which offers the ability to sort through major design alternatives quickly while assisting in the interpretation of experimental data. Previously, detailed catalyst models have been developed which require the specification of intricate kinetic mechanisms to determine overall catalyst performance. While yielding extremely valuable results, these models use complex numerical algorithms to solve multiple partial differential equations which are time consuming and occasionally numerically unstable.
Technical Paper

Application of Catalyzed Hydrocarbon Traps to Reduce Hydrocarbon Emissions from Ethanol Flex-Fuel Vehicles

Catalyzed hydrocarbon traps have shown promise in reducing cold-start tailpipe hydrocarbon emissions from gasoline powered vehicles. In this paper, we report the use of catalyzed hydrocarbon trap technology to reduce the non-methane hydrocarbon emissions from a flex-fuel vehicle that can operate on fuel mixtures ranging from pure gasoline to 85% ethanol/15% gasoline. We have found that hydrocarbon traps show a substantially greater reduction in hydrocarbon emissions when used with ethanol fuel than with gasoline. We present laboratory and vehicle test results that show that tailpipe non-methane hydrocarbon emissions from a flex-fuel vehicle can be reduced by 43% when using 85% ethanol/15% gasoline fuel and 16% when using gasoline fuel from a baseline exhaust system using a three-way catalyst. These results were obtained using a catalyzed hydrocarbon trap specifically formulated for use with ethanol fuel.
Technical Paper

Use of a Novel Non-Phosphorus Antiwear Additive for Engine Oils

A novel non-phosphorus antiwear additive, NP-1, was evaluated as a partial substitute for zinc dialkyldithiophosphate (ZDTP). ZDTP, an antiwear/antioxidant engine oil additive may under certain conditions cause three way catalyst (TWC) deactivation due to formation of an amorphous zinc pyrophosphate, Zn2P2O7, glaze. Antiwear and antioxidant properties of NP-1 alone and in combination with ZDTP were compared with ZDTP only containing formulations. The effects of NP-1 on TWC activity during pulsator modulation and steady-state conditions showed that the TWC maintained good overall activity during 24,000 simulated miles.
Technical Paper

Techniques for Analyzing Thermal Deactivation of Automotive Catalysts

Automotive three-way catalysts (TWC) were characterized using temperature-programmed reduction (TPR), x-ray diffraction (XRD), Raman spectroscopy, chemisorption measurements and laboratory activity measurements. Capabilities and limitations of these standard analytical techniques for the characterization of production-type automotive catalysts are pointed out. With the exception of chemisorption techniques, all appear to have general utility for analyzing exhaust catalysts. The techniques were used to show that the noble metals and ceria in fresh Pt/Rh and Pd/Rh catalysts are initially highly dispersed and contain a mixture of interacting and non-interacting species. Thermal aging of these catalysts (in the reactor or vehicle) caused both precious metal and ceria particles to sinter, thereby decreasing the interaction between the two.
Technical Paper

A Feedback A/F Control System for Low Emission Vehicles

Recent Federal and California legislation have mandated major improvements in emission control. Tailpipe HC emission must be decreased an order of magnitude for the California Ultra Low Emission Vehicle (ULEV) standard. Present feedback A/F* control systems employ a Heated Exhaust Gas Oxygen sensor (HEGO sensor) upstream of the catalyst to perform A/F feedback control. Limitations on the ultimate accuracy of these switching sensors are well known. To overcome these limitations a linear Universal Exhaust Gas Oxygen sensor (UEGO sensor) placed downstream from the minicatalyst is employed to attain improved A/F control and therefore, higher three-way catalyst (TWC) conversion efficiency. This configuration was granted a patent in 1992 (1**). This study compares performance differences between the two feedback control systems on a Ford Mustang. In initial studies both the UEGO and HEGO sensors were compared at the midposition location downstream of a minicatalyst.
Technical Paper

The Microcomputer Based Engine Control System for the IIEC-2 Concept Car

The microcomputer based ignition timing, EGR and fuel injection control system for the IIEC-2 concept vehicle is described. The techniques used to compensate the fuel delivery for EGR, to minimize response time and to compensate for engine and injector non-uniformity are emphasized. These measures, in conjunction with limit cycle air/fuel ratio control utilizing feedback from an exhaust gas oxygen sensor, are examined with respect to the effect on three-way catalyst performance.
Technical Paper

Dynamometer Test Procedures for Three-Way Catalyst Screening

Procedures are described for rapidly aging and for testing three-way catalysts on an engine dynamometer which are relatable to actual vehicle aging and CVS testing. The accelerated aging cycle consists of a modification of the AMA durability driving cycle; testing consists of the measurement of HC, CO and NOx conversion as a function of A/F with superimposed perturbations which simulate limit cycle variations of A/F in a closed-loop fuel control system.
Technical Paper

Effect of Mileage Accumulation on Particulate Emissions from Vehicles Using Gasoline with Methylcyclopentadienyl Manganese Tricarbonyl

Particulate and manganese mass emissions have been measured as a function of mileage for four Escort and four Explorer vehicles using 1) MMT (Methylcyclopentadienyl Manganese Tricarbonyl) added to the gasoline at 1/32 g Mn/gal and 2) gasoline without MMT. The MMT was used in half of the fleet starting at 5,000 miles. The vehicles were driven on public roads at an average speed of 54 mph to accumulate mileage. This report describes the particulate and manganese emissions, plus emissions of four air toxics at 5,000, 20,000, 55,000, 85,000 and 105,000 miles. Four non-regulated emissions were measured and their average values for vehicles without MMT were 0.6 mg/mi for formaldehyde, 0.7 mg/mi for 1,3-butadiene, 9 mg/mi for benzene and 12 mg/mi for toluene. Corresponding values for MMT-fueled vehicles were between 1.5 and 2.4 times higher.
Technical Paper

Modeling Current Generation Catalytic Converters: Laboratory Experiments and Kinetic Parameter Optimization - Steady State Kinetics

An experimental data base of catalyst conversion efficiency was generated, using a tubular flow reactor which contained either a Pt/Rh (5:1; 40g/ft3) or a Pd/Rh (5:1; 40g/ft3) catalyst sample, for the purpose of updating the kinetic rate constants in the Ford TWC model. Steady-state conversion efficiency of CO, NO, C3H8, C3H6, H2 and O2 through these catalysts were determined for a variety of inlet species concentrations and inlet gas temperatures. These data were obtained for values of redox ratio between 0.5 (excess O2) and 4.0, and inlet gas temperatures between 371°C and 593°C. All experimental details and modeling procedures utilized in obtaining an optimized set of kinetic parameters are included. Results of these experiments show significant improvement in CO and NO conversion efficiency and an increase in NH3 production for both catalyst formulations over previous generation catalyst formulations when redox ratio is greater than unity.
Technical Paper

Development of Pd-only Three Way Catalyst Technology

In joint partnership with its catalyst suppliers, Ford has made significant advances in the performance of Pd-only three way catalyst (TWC) technology through improvements in catalyst oxygen storage. The following manuscript describes in detail the performance advancement of Ford's Pd-only washcoat technology through the use of laboratory, engine dynamometer, and vehicle emission data.
Technical Paper

Scavenging of a Firing Two-Stroke Spark-Ignition Engine

Current demands for high fuel efficiency and low emissions in automotive powerplants have drawn attention to the two-stroke engine configuration. The present study measured trapping and scavenging efficiencies of a firing two-stroke spark-ignition engine by in-cylinder gas composition analysis. Intermediate results of the procedure included the trapped air-fuel ratio and residual exhaust gas fraction. Samples, acquired with a fast-acting electromagnetic valve installed in the cylinder head, were taken of the unburned mixture without fuel injection and of the burned gases prior to exhaust port opening, at engine speeds of 1000 to 3000 rpm and at 10 to 100% of full load. A semi-empirical, zero-dimensional scavenging model was developed based on modification of the non-isothermal, perfect-mixing model. Comparison to the experimental data shows good agreement.
Technical Paper

Ford Three-Way Catalyst and Feedback Fuel Control System

The objective of this paper is to describe the Ford Motor Company (Ford) approach of meeting exhaust emission regulations with a three-way catalyst and feedback control system. A pilot program was initiated to gain production experience with three-way catalyst systems in anticipation of expanded usage to meet future emission standards. The Ford system consists of a three-way catalyst with feedback control monitoring the exhaust oxygen concentration and controlling the fuel flow to produce a stoichiometric exhaust mixture. Mixture control is critical since catalyst NOx conversion efficiency is diminished when the exhaust mixture deviates from stoichiometry. Briefly, the control loop consists of zirconium dioxide exhaust sensor to indicate oxygen concentration, an electronic control unit, a vacuum regulator to proportion a vacuum signal to the carburetor, and a feedback controlled carburetor with vacuum modulated main fuel system.
Journal Article

Hydrogen DI Dual Zone Combustion System

Internal combustion (IC) engines fueled by hydrogen are among the most efficient means of converting chemical energy to mechanical work. The exhaust has near-zero carbon-based emissions, and the engines can be operated in a manner in which pollutants are minimal. In addition, in automotive applications, hydrogen engines have the potential for efficiencies higher than fuel cells.[1] In addition, hydrogen engines are likely to have a small increase in engine costs compared to conventionally fueled engines. However, there are challenges to using hydrogen in IC engines. In particular, efficient combustion of hydrogen in engines produces nitrogen oxides (NOx) that generally cannot be treated with conventional three-way catalysts. This work presents the results of experiments which consider changes in direct injection hydrogen engine design to improve engine performance, consisting primarily of engine efficiency and NOx emissions.