Selection and development of a reactor for diesel particulate filtration

Abstract

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-purpose chemical reactor for environmental protection, can lower the emission of diesel soot particles. The aim is to develop a diesel particulate filter that is robust, dependable, energy efficient and resistant to plugging. Moreover, ultrafine particles should be trapped and no poisoning gases should be emitted. A strategic approach is used for the design of a diesel particulate filter, inspired by the method of Krishna and Sie (1994) Chemical Engineering Science 49, 4029–4065, for multiphase reactor selection. The method involves three strategic levels for reactor selection: catalyst design, heat and mass injection and dispersion, and hydrodynamic flow regime; in this paper, the emphasis is on hydrodynamics. This approach has led to the design of a novel filter type for diesel soot filtration: the turbulent precipitator with foam collector plates. In this filter the gas flow is divided over two zones with different hydrodynamic characteristics: fast gas flow in an open channel and slow gas flow in stagnant zones. The open channel enables low pressure drop and prevents plugging, the stagnant zones enable deposition of diesel soot particles and, if desired, the placement of the catalytic material. The results for two different geometries of the turbulent precipitator are presented, they indicate that 90 ppi ceramic foam collector plates perform the best and that it is possible to tune different turbulent precipitators for different diesel engines. Computational fluid dynamics can be used to optimize the turbulent precipitator because it identifies the two hydrodynamic zones in the filter.