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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.

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 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.

A diesel emission control system, which can simultaneously reduce particulate and NOx emissions through filtration and particle-free Exhaust Gas Recirculation (EGR) has been developed and tested. The key element of the system is a novel ceramic fitter which has shown virtually complete soot removal from diesel exhaust streams. Regeneration of the filter was accomplished by periodically backpulsing the filter with short pulses of compressed air. Testing of the system was carried out using a Caterpillar generator set powered by a 65 kW diesel engine, and a separate load bank which allowed the engine to operate at various load settings. The filter unit consisted of four CeraMem filters (150 mm2 x 305 mm long, 4 mm2 cell), a backpulsing system for filter regeneration, and a baghouse for soot collection. NOx reduction of 75% was achieved at full engine load and a 30% EGR rate.

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 work determined the suitability of two silicon carbide (SiC) monoliths (one regular and one coated with a micromembrane), as well as a coated cordierite monolith for use as aerodynamically regenerated particulate filters for diesel engines. These ceramic honeycomb monoliths were tested for their filtration efficiency, their post filtration particulate size distribution and their ability to be aerodynamically regenerated at pre-selected operating temperatures (200, 300 and 400°C). Through combined laboratory and field testing, the uncoated silicon carbide filter produced the most satisfactory results in all of these tests. This filter resulted in excellent regeneration characteristics while maintaining the highest filtration efficiencies at all particle sized tested. All filters were found to clean effectively at all temperatures. However, upon normalization with the volumetric flow rate through the monolith, it was found that the filters were most thoroughly cleaned at 400°C.