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New developments on the Northeastern University's Rotating Self-Cleaning particulate trap are reported herein. A new and improved system has been constructed with emphasis placed on minimizing leaks around rotating parts. Five different, wall flow, ceramic monolith filter elements were tested, a Corning, two NGK, a Panasonic and a Corning/Ceramem trap. The filters were rotated to enable simultaneous capture of the particulate emissions and regeneration by removing the particulates using compressed air. Improvements on the casing, the ducts, and the sealing around the monolith provided for an air-tight casing, and for almost complete isolation between the exhaust and the cleaning air streams. Moreover, experiments were conducted to minimize the flowrate of the required cleaning air.

A rotating, self-cleaning particulate trap device has been developed and tested coupled with the exhaust of a single cylinder compression ignition engine. This trap design does not require thermal regeneration to burn the collected particles. Instead, it involves a continuous self-cleaning process, thereby eliminating some of the most persistent problems associated with material failure during regeneration. Captured particulates are blown out of the trap in a reverse flow configuration and they are collected on a fabric filter. Initial tests at high engine loadings showed that the system performs satisfactorily, although further improvements are necessary to render the device suitable for long term applications. Numerical modelling techniques are also employed to study the flow patterns in the trap assembly and aid in the optimization of the system.

A new design of a self-cleaning diesel particulate trap is discussed herein. Past research at Northeastern University has demonstrated the feasibility of using compressed air, counterflow to the exhaust, for regeneration of ceramic wall-flow particulate traps, thus, eliminating the need for thermal regeneration. The performance of these systems, however satisfactory it might have been, was hindered by potential reliability problems of mechanical components such as rotating monoliths and collection of soot in bag houses. Thus, the present work concentrated in designing a reliable and inexpensive system incorporating passive regeneration devices and a soot incinerator. Upon satisfactory completion of laboratory bench-scale tests, the system was mounted on a 1.4 liter diesel-powered vehicle and was field-tested for 2000 km. The core of the system is a high soot collection efficiency ceramic monolith.

The development of new designs of a diesel particulate control system is discussed herein. The system employs a single high collection efficiency ceramic monolith to filter the particulate emissions of the engine. Regeneration is achieved by intermittent pulses of pressurized reverse-flow air. After every regeneration the soot is collected at the bottom of the device where it is burned in an incinerator chamber. Different configurations of the system were tested satisfactorily for performance and durability for 100 hrs, coupled to a small experimental engine which was sooting at high rates. Subsequently, a system incorporating a long ventless chamber fitted with an electric burner was mounted on a diesel passenger car and tested for on-road performance evaluation and further development.

This study demonstrated the concept of using exhaust gas recirculation (EGR), coupled with a high-collection efficiency particulate trap to simultaneously control smoke, unburned hydrocarbon and NOx emissions from diesel engines. Although EGR technology has been extensively used in gasoline engines, its application to diesel engines has been hindered by the particulate content of the recirculated exhaust gas. Even with the use of conventional ceramic monolith filters, with soot collection efficiencies in the range of 50-80%, the exhaust stream is not adequately clean for recirculation to the engine. This investigation used a high soot collection efficiency Ceramem filter to make EGR possible. This ceramic filter is coated with a thin microporous ceramic membrane to provide soot removal efficiencies in the order of 99%.

The development of an Aerodynamically Regenerated Trap (ART) with a flow-through incinerator section is discussed herein. The ART system presented herein employes a single high-collection efficiency ceramic monolith to filter particulate emissions. Regeneration is performed aerodynamically, using compressed air flowing in the direction opposite to the exhaust flow. Dislodged particulates are captured in the incineration section of the trap directly below the ceramic monolith, where they are burned using an electric heater. This work concentrates on the design and development of the incinerator sections of the diesel particulate trap, whose function is to retain the soot from the regeneration air stream, without impeding the flow of the regeneration air itself.

The simultaneous control of diesel engine particulate and NOx emissions was targeted in this study. Particulate control was achieved with a trap that incorporated a high-filtration efficiency ceramic honeycomb monolith. Aerodynamic regeneration was used to periodically backflush the monolith filter. Soot was collected in a metallic chamber and was either incinerated by an electric burner or removed by a vacuum cleaner. NOx emissions were reduced by recirculation of filtered exhaust gases (EGR), which was made possible by the high collection efficiency of the employed monoliths. Tests were conducted on the road, driving a diesel vehicle under various loads and speeds. The levels of NO, CO and O2 at the exhaust were continuously monitored using a portable instrument. The particulate filtration efficiency was in the vicinity of 99% using CeraMem and 97-98% using Panasonic traps, respectively, hence the EGR line was effectively particulate-free.

The development of a soot incinerator with dual ceramic filters and an electric strip heater is discussed herein. The incinerator is designed to operate in series with a diesel particulate trap developed previously (1).1 The particulate trap consists of a primary ceramic monolith which serves as the filtering device. Once the primary monolith has collected enough soot from the exhaust flow to induce a substantial amount of back pressure to the engine, it is cleaned aerodynamically using short pulses of compressed air. The soot is then forced through a reed valve and into the incinerator chamber, where some of the particulates come in contact with an electric strip heater and burn. The regeneration air exits the incinerator through two secondary ceramic wall-flow rectangular filters, where any unburned particulates are retained. Filtered regeneration air is, thus, released to the atmosphere.

A novel high-efficiency Pallflex filter has been developed for diesel exhaust after-treatment. The filter media is made of high-melting point boro-silicate glass fibers bonded together to form a paper-like pad that can withstand elevated thermal regeneration temperatures. Each filter element is placed between two fine stainless steel wire meshes, which impart structural rigidity to the fiber matrix and prevent its disintegration. An array of these filter pads, placed 1 cm, apart, is assembled together in an insulated housing. The filters are separated by spacers, which are perforated on one side and plugged on the other side to force the exhaust to flow through the filter elements. Such a trap of a total filter surface area of 1.2 m2 and a volume of 14 liters was tested in the laboratory and on the road to determine its filtration efficiency, back pressure characteristics and regenerability.

This is an optimization study on the use of filtered exhaust gas recirculation (EGR) to reduce the NO emissions of diesel engines. Control of the particulate emissions and provisions for filtered EGR were achieved by an Aerodynamically Regenerated Trap (ART) with collection efficiencies in the order of 99%. The amount of EGR was regulated to provide for substantial NO reduction, without unacceptably decreasing the thermal efficiency of the engine or increasing the CO emissions. EGR regulation was accomplished by monitoring the injection pump setting which was correlated to the fuel flow rate, the speed of the engine, the amount of EGR flow, and the ambient air temperature. Through these parameters, the mixture strength expressed as the equivalence ratio, ϕ, was calculated and related to the power output of the engine. Thus, a map of engine performance parameters was generated and related to measured NO and CO emissions.

New developments for optimized control of Aerodynamically Regenerated Traps (ART) - Exhaust Gas Recirculation (EGR) integrated systems for diesel engines are presented herein. Such systems employ high-efficiency ceramic monolith filters to retain 99% of the emitted particulates. Regeneration is achieved periodically by short pulses of compressed air, flowing in the opposite direction to the exhaust. The soot is collected in a chamber, outside of the monolith, where it is oxidized with an electric burner. A fraction of the filtered exhaust is returned to the engine and this reduces NOx emissions, typically, by more than 50% at 18% EGR. However, since the amount of EGR, the frequency of regeneration and the frequency and duration of burning have a bearing on the fuel consumption of the engine, their optimization is imperative. Thus, provisions were made to collect intelligent information, leading to continuous assessment of the engine performance and fuel economy.

This manuscript describes laboratory tests and calculations that explore the effectiveness of a stream of ionized air to oxidize soot and, thus, regenerate diesel particulate filters. Soot was oxidized inside a muffle furnace in two different configurations, either as a layer of soot spread in a porcelain boat, or as a quantity of soot evenly loaded in a ceramic wall-flow monolith. Oxidation took place in air, ozone-enriched air or air ionized by an electric arc (thermal plasma), at furnace temperatures in the range of 200-450° C. It was found that when ozone was generated in the inlet air (1060 ppm) the consumption rate of soot increased by up to ten percent. However at the presence of the thermal plasma (generating O, NO2, NO, and O3) the carbon consumption was accelerated by factors varying from a few percent to often exceeding one hundred percent. The effectiveness of this technique depended on the characteristics of the arc.