Electrostatic collection of diesel particles

Diesel particles carry charges ranging from 1-5 units of elementary charge per particle. The charge is bipolar, i.e., there are approximately equal numbers of positively and negatively charged particles. The charge distribution with respect to size follows a high temperature, Boltzmann equilibrium relationship. The first part of this paper describes charge measurements made on diesel particles emitted by three different diesel engines, and postulates a charging mechanism. The second part of the paper is an examination of how this natural charge may be used to collect particles from the exhaust. The charge level produced by combustion is only slightly lower than the charge level produced by the corona discharge in a conventional electrostatic precipitator. Thus, a simple electrostatic precipitator without a corona section will collect diesel particles affectively. The absence of a corona is a great advantage over a conventional precipitator because the corona is the main power consumer in an electrostatic precipitator. A model precipitator was built and tested on the exhaust from several engines. It was found-to be very effective after moving diesel particles with efficiencies ranging from 70-90%. Model tests and the design of a full scale particle collection device based on a corona-less electrostatic precipitator are described.