CHARGING MECHANISM OF SUBMICRON DIESEL PARTICLES

The charging mechanism of submicron diesel particles has been studied experimentally and theoretically. Actual charge levels of diesel particles were measured. Three different diesel engines were used: a light-duty VW Rabbit and medium-duty John Deere and Oliver engines.; The volatile and charged fraction were measured as a function of engine load. The charged fractions varied from 20 to 80% by volume, depending on engine load and type. Generally, a higher load gave low volatile fractions and high charged fractions.; Average charge levels of diesel particles were measured at several particle sizes. The measured average charge per particle varied from 1 to 4 elementary charge units as particle diameter varied from 0.047 to 0.266 (mu)m. Essentially, equal concentrations of positively and negatively charged particles were observed for all sizes of particles.; Charged distributions were also measured at several different particle sizes. Charge distributions for particles smaller than 0.133 (mu)m diameter were in good agreement with a Boltzmann equilibrium distribution for a temperature in the 1300-1400K range. However, the larger particles gave progressively broader distributions than Boltzmann equilibrium.