The performance of an electrostatic agglomerator as a diesel soot emission control device

A major problem with many soot emission control devices is the fact that they quickly become loaded with soot which must be removed by a controlled burning (regeneration) process. The need for regeneration greatly complicates such diesel particle emission control devices. In this paper, an electrostatic agglomerator (ESA) which efficiently collects diesel particles but does not require regeneration is described. The ESA is an electrostatic precipitator which is designed to collect and subsequently reentrain diesel soot particles. The collection and reentrainment processes results in growth of particle diameter from roughly 0.2 μm to larger than 1.0 μm. The agglomerated particles are large enough to be collected by a relatively simple inertial device, e.g., a cyclone separator. The collected particle may be either recycled to the engine or disposed of by other means. Electrostatic collection is made easier by the fact that diesel particles are charged by the combustion process itself. This makes it unnecessary to employ a corona charging section. As a result relatively low voltages (3-5 kV) and currents (1-2 mA) may be employed. The paper describes the design and performance of a prototype electrostatic agglomerator fitted to a Caterpillar 3304 indirect-injection, naturally-aspirated diesel engine. Performance of the device is described in terms of its ability to shift the diameter of the particles upward from the sub-micron range into the super-micron range.