Charge-to-mass ratio and dendrite structure of diesel particulate matter charged by corona discharge

The electric charge of diesel particulate matter (DPM) from a corona discharge device is measured for understanding the electrical characteristics of the DPM; an electrostatic precipitator (ESP) is employed for trapping DPM. Exhaust gas from a diesel engine is sampled by isokinetic sampling, and DPM contained in the gas is charged by negative corona discharge. The charged DPM is collected by a Faraday cup, and its electric charge is measured by a Coulomb meter. In addition, the appearance of the collected DPM is observed using a scanning electron microscope. It is found that when the gas velocity is 0.28 m/s, the maximum charge-to-mass ratio of the DPM is −126 μC/g. The DPM appears to agglomerate into a large particle in the absence of corona discharge; however, the agglomerated DPM forms a dendrite structure in the presence of corona discharge. The dendrite structure causes an increase in the surface area of the agglomerated DPM. Therefore, the oxidation removal of the DPM trapped by the ESP by using ozone and nitrogen dioxide can be enhanced because an oxidation reaction occurs on the surface of the DPM.