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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.

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.

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.