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Technical Paper

Validation Method for Diesel Particulate Filter Durability

The diesel particulate filter (DPF) is a critical aftertreatment device for control of particulate matter (PM) emissions from a diesel engine. DPF survivability is challenged by several key factors such as: excessive thermal stress due to DPF runaway regenerations (or uncontrolled regeneration) may cause DPF substrate and washcoat failure. Catalyst poisoning elements from the diesel fuel and engine oil may cause performance degradation of the catalyzed DPF. Harsh vibration from the powertrain, as well as from the road surface, may lead to mechanical failure of the substrate and/or the matting material. Evaluations of these important validation parameters were performed.
Technical Paper

Feasibility Investigation of a High-Efficiency NOx Aftertreatment System for Diesel Engines

A high-efficiency NOx aftertreatment system has been proposed for use in Diesel engines. This system includes a Lean NOx Trap (LNT) in series with a Selective Catalyst Reduction (SCR) catalyst [6], [7], [8], and is hereinafter referred to as the LNT-SCR system. The combined LNT-SCR system can potentially overcome many of the drawbacks of LNT-only and SCR-only operation and achieve very high NOx conversion efficiency without external addition of ammonia (or urea). A laboratory test procedure was developed to validate the LNT-SCR system concept, and a series of tests was conducted to test the NOx conversion of this system under various conditions. A Synthetic Gas Reactor (SGR) system was modified to accommodate LNT and SCR catalyst cores and synthetic gas mixtures were used to simulate rich-lean regeneration cycles from a diesel engine. A Fourier Transform Infrared (FTIR) system was used to measure gas compositions within the LNT-SCR system.
Technical Paper

Methodologies to Control DPF Uncontrolled Regenerations

Diesel particulate filters (DPF) have been shown to effectively reduce particulate emissions from diesel engines. However, uncontrolled DPF regeneration can easily damage the DPF. In this paper, three different types of uncontrolled DPF regeneration are defined. They are: Type A: Uncontrolled high initial exotherm at the start of DPF regeneration, Type B: “Runaway” or uncontrolled regeneration, which takes place when the engine goes to idle during normal DPF regeneration, and Type C: Uneven soot distribution causing excess thermal stress during normal DPF regeneration. In this paper, different control strategies are developed for each of the three types of uncontrolled DPF regenerations. These control strategies include SOF control, exhaust flow pattern improvement, as well as EGR control through intake throttling and A/F ratio control.
Journal Article

EGR System Fouling Control

Exhaust gas recirculation (EGR) is effective in reducing engine-out NOx emissions; however, the EGR system is subject to fouling and corrosion. Fouling is mainly due to particulate buildup on the EGR component (e.g., EGR valve and cooler) surfaces. Corrosion is primarily related to oxides of sulfur and nitrogen in the gas stream, especially problematic when condensation occurs [1]. Because cooled EGR is most effective in controlling NOx emissions, EGR cooler design and operation are important considerations in engine design in order to meet durability requirements. An approach has been developed to greatly reduce EGR system fouling. Four EGR coolers were tested simultaneously with various PM control devices installed upstream of the cooler. System configuration and on-engine test results are presented herein.
Technical Paper

Simultaneous Reduction of PM, HC, CO and NOx Emissions from a GDI Engine

Particulate Matter (PM) emissions from gasoline direct injection (GDI) engines are becoming a concern and will be limited by future emissions regulations, such as the upcoming Euro 6 legislation. Therefore, PM control from a GDI engine will be required in addition to effective reduction of HC, CO and NOx emissions. Three different integrated aftertreatment systems were developed to simultaneously reduce PM, HC, CO and NOx emissions from a preproduction Ford 3.5L EcoBoost GTDI engine, with PM reduction as the major focus. PM reduction efficiencies were calculated based on the measurements of PM mass and solid particle number. Test results show that tradeoffs exist in the design of aftertreatment systems to significantly reduce PM emissions from a GDI engine.
Technical Paper

SCR Deactivation Kinetics for Model-Based Control and Accelerated Aging Applications

Selective Catalytic Reduction (SCR) catalysts are used to reduce NOx emissions from internal combustion engines in a variety of applications. Southwest Research Institute (SwRI) performed an Internal Research & Development project to study SCR catalyst thermal deactivation. The study included a V/W/TiO₂ formulation, a Cu-zeolite formulation and a Fe-zeolite formulation. This work describes NH₃ storage capacity measurement data as a function of aging time and temperature. Addressing one objective of the work, these data can be used in model-based control algorithms to calculate the current NH₃ storage capacity of an SCR catalyst operating in the field, based on time and temperature history. The model-based control then uses the calculated value for effective DEF control and prevention of excessive NH₃ slip. Addressing a second objective of the work, accelerated thermal aging of SCR catalysts may be achieved by elevating temperatures above normal operating temperatures.
Technical Paper

Dependence of Fuel Consumption on Engine Backpressure Generated by a DPF

In recent years, Diesel Particulate Filter (DPF) systems have become the state-of-the-art technology to realize low particulate emission for light, medium or heavy-duty diesel vehicles. In addition to good filtration efficiency and thermo-mechanical robustness, the engine backpressure resulted from the DPF installation is an important parameter which directly impacts the fuel economy of the engine. The goal of this experimental test series was to determine the dependence of fuel consumption on engine backpressure resulted from a DPF installed on a heavy-duty application. The testing was executed on a MY2003 Volvo D12 heavy-duty diesel engine in an engine test cell at Southwest Research Institute (SwRI). Empty DPF cans were used with an exhaust valve to mimic the post turbo pressure levels for two different types of DPF materials at nine selected engine operating points of the European Stationary Cycle (ESC).
Technical Paper

Development of a Novel Device to Improve Urea Evaporation, Mixing and Distribution to Enhance SCR Performance

A novel urea evaporation and mixing device has been developed to improve the overall performance of a urea-SCR system. The device was tested with a MY2007 Cummins ISB 6.7L diesel engine equipped with an SCR aftertreatment system. Test results show that the device effectively improved the overall NO conversion efficiency of the SCR catalyst over both steady-state and transient engine operating conditions, while NH₃ slip from the catalyst decreased.