Selection and development of a reactor for diesel particulate filtration

The diesel engine is an efficient power generator but its exhaust gas needs to be cleaned. A diesel particulate filter, in fact a multi-phase multi-pu rpose chemical reactor for environmental protection, can lower the emission of diesel soot particles. The aim is to develop a diesel particulate filte r that is robust, dependable, energy efficient and resistant to plugging. M oreover, ultrafine particles should be trapped and no poisoning gases shoul d be emitted. A strategic approach is used for the design of a diesel parti culate filter, inspired by the method of Krishna and Sie (1994) Chemical En gineering Science 49, 4029-4065, for multiphase reactor selection. The meth od involves three strategic levels for reactor selection: catalyst design, heat and mass injection and dispersion, and hydrodynamic flow regime; in th is paper, the emphasis is on hydrodynamics. This approach has led to the de sign of a novel filter type for diesel soot filtration: the turbulent preci pitator with foam collector plates. In this alter the gas flow is divided o ver two zones with different hydrodynamic characteristics: fast gas flow in an open channel and slow gas flow in stagnant zones. The open channel enab les low pressure drop and prevents plugging, the stagnant zones enable depo sition of diesel soot particles and, if desired, the placement of the catal ytic material. The results for two different geometries of the turbulent pr ecipitator an presented, they indicate that 90 ppi ceramic foam collector p lates perform the best and that it is possible to tune different turbulent precipitators for different diesel engines. Computational fluid dynamics ca n be used to optimize the turbulent precipitator because it identifies the two hydrodynamic zones in the filter. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.