Effect of the Number of Pairs of Dielectric Barrier Discharge Reactor on Diesel Particulate Matter Removal and Pressure Drop

Worldwide emission regulations on diesel particulate matter (PM) into the atmosphere have become more stringent. In Japan a new vehicular emission regulation, so called “post new long term regulation”, will be introduced since 2009. In this regulation, PM emission rate is should be less than 0.005 g/km. We have developed an uneven type of dielectric barrier discharge (DBD) reactor, which consists of uneven alumina plates and uneven stainless steel plates, to comply with the regulation. PM emitted from a diesel engine (4-cycle, direct Injection, 2 liter) was oxidized by some active oxygen species produced by the corona discharges. The PM emission rate under conditions with or without corona discharges was measured. The pressure drop in the DBD reactor was measured at the inlet of the DBD reactor. The energy efficiency and pressure drop are very important. In this study, we investigated the effect of the number of pairs of the alumina plate and stainless steel plate on the performance of the reactor because the rise in the number of the pairs of the uneven alumina and stainless steel plates can be generally considered to increase the energy efficiency and decrease the pressure drop. When the engine output was 3.0 kW, PM removal ratio and energy efficiency using 20 pairs were 47-84% and 2.9-0.85 g-PM/kWh, respectively, in the range of injection energy of 84-340 W. When 50 pairs were used, the energy efficiency was greatly increased to 13.7-3.6 g-PM/kWh. PM removal ratio was 86% at the injection energy of 87 W and reached 94% at 250 W. The rise in the number of pairs from 20 to 30 or 50 increases the opening space and discharge (reaction) area of the reactor. Thus, the increase in PM removal ratio and energy efficiency is due to the increase in the discharge area. The pressure drop was 6.8 and 4.3 kPa when 20 or 30 pairs were used. The pressure drop was reduced to 2.3 kPa, which corresponds to the 2.9% energy loss, by using 50 pairs by the increase of opening space of the reactor. It was found that the energy efficiency of PM removal is inversely proportional to the approximately 1.6 power of the space velocity and that the pressure drop is proportional to the 1.2 power of the space velocity. Based on the regression curve, it was found that 56 pairs of the uneven alumina and stainless plates can provide an energy loss due to pressure drop smaller than 2 %.