Study On Charging Characteristics Of Diesel Particles Enhanced By Corona Discharge

Diesel particle matter pose a threat to air environment and human health because of the high number concentration of nanometer particles.Although the application of after-treatment technology can decrease the total mass of diesel particle matter,it is still a big problem to control the particle number emission of diesel engine.Electric agglomeration technology which is considered as an effective way to reduce the number of nanometer particle matter can charge particles and promote the agglomeration of charged particles.The key of electric agglomeration is particle charging.The charge of particles plays an important role in the particles motion and coagulation processes.Therefore,the charging characteristics of diesel particles enhanced by corona discharge were studied in this dissertation.The specific research works are as follows:In order to determine the appropriate structure parameters of discharge reactor,current-voltage characteristic of wire-cylinder type corona discharge reactor was studied.The mathematical model for current-voltage characteristic was built by theoretical analysis.The relation between discharge current and voltage was obtained when the wire radius is 0.3 mm,0.5 mm and 1.0 mm,and cylinder radius is 50 mm,100 mm and 150 mm respectively.The results show that the discharge current increases with the decrease of wire radius and cylinder radius,but the corona onset and breakdown voltage have a decline under this condition.The charging test bench which was applied for diesel particles enhanced by corona discharge was set up.Zeta potential of diesel particle was used to represent the charged state and the charge of particles could be calculated according to the value of Zeta potential;Influences of various factors on the charge of particles were investigated by changing the charged voltage,internal temperature of charging zone and the load of engine.Experimental results show that the increase of charged voltage can increase the charge and the absolute value of Zeta potential.With increase of charging zone temperature,corona inception voltage declines and the charge of particle increases.The load of engine has a positive effect on the charge of particles which reaches its peak at full load.Influences of corona discharge on particle number concentration,particle mass median diameter and surface morphology were investigated with the application of engine exhaust particle size and scanning electron microscope.It is clearly revealed that corona discharge benefits the decrease of total particle number and nucleation mode particle number owing to the agglomeration of charged diesel particles.The number concentration of accumulation mode particles(>93.1 nm)has a rise with the increase of discharge voltage.At 100% load,particle mass median diameter decreases from 99.72 nm to 108.62 nm and the growth rate is 8.92% as the discharge voltage increases from 0 kV to-20 kV.Furthermore,the uncharged particles show stone clusters structure and particles enhanced by corona discharged show chain structure.