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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%.

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.