This paper is aimed at investigating thoroughly the corona performance in the wirecylinder ESP with and without loading by suspended particles in the exhaust of a diesel engine. The onset voltage of negative corona on the discharge wire is calculated based on the criterion of self-sustained discharge. The ionized space between the discharge wire and the collecting cylinder of the ESP is mathematically modeled for calculating the spatial distribution of the space-charge density due to both the ions and the charged particles as well as the components of the electric field including the applied field and the field due to the space charge. This is in addition to the calculation of the currentvoltage characteristics of the ESP with and without particle loading.