Removal of soot in diesel exhaust gases by a combination of DC corona discharge and oil bath

Abstract

Summary form only given. The soot emission from diesel engine is becoming a big environmental problem. However, the particulate size of soot is so small that the conventional filter technology does not work well. The authors have set up an experimental soot removal system consisted of a combination of DC corona discharge device and oil bath. The DC corona discharge device has several thin wires on a plate electrode with a gap distance of 30mm and the plate electrode is immersed in an oil bath. Several shapes of plate electrodes are prepared for the tests. The high negative polarity DC voltage is applied to the wire electrodes, which emits electrons into the space between wire electrodes and a plate electrode. Exhaust gases from diesel engine are led to the discharge space, which give charges to suspended particles in the gases. The electrostatic force attracts the charged particles to the oil bath and adsorbed them into oil. The experiments were carried out using a 2.4kVA diesel engine and exhaust gases of 8m/sup 3//h were led to the system. DC voltage of about 20kV was applied to the electrodes and the amount of suspended particles adsorbed in the oil bath was measured. The authors developed a measuring method of particles absorbed in oil by measuring the absorption of a laser beam through the oil muddied by carbon particles. Calibrations were carried out with some sample oil muddied with known amounts of carbon particles. The soot removal tests were carried out under various electrode conditions. The number of wires tested was 3 to 7 and the distance between wires was changed between 10 to 70mm. Oil was filled in the bath in a depth of 5mm. The discharge currents were measured on the electrodes tested. From the test results, it was estimated that oil adsorbed about 58mg of carbon particles in a ten minutes test. This amount was estimated as about 85% of the total amount of particles exhausted from the engine. The test results suggest that this method is very attractive to remove suspended particles in exhaust gases.