Repetitively pulsed plasma remediation of NOx in soot laden exhaust using dielectric barrier discharges

Abstract

The removal of NOx from diesel exhausts is being investigated using a variety of repetitively pulsed plasma sources. Soot particles influence NOx densities in the gas phase of these devices through heterogeneous reactions on the soot surface. In repetitively pulsed devices, such as dielectric barrier discharges, the starting gas composition of any given pulse depends on the homogeneous and heterogeneous chemistry occurring during previous pulses. In this regard, we have computationally investigated the consequences of repetitive discharge pulses and heterogeneous chemistry on remediation of NOx and soot oxidation. In the absence of soot, a series of discharge pulses results in increased conversion of NO to NO2 compared to depositing the same energy in a single discharge pulse. With soot, single pulses result in an initial gas phase oxidation of NO to NO2, followed by heterogeneous conversion of NO2 to NO on the soot. With multiple pulses and soot, due to the larger gas phase density of NO2, there is an increased flux of NO2 to the soot surface, resulting in increased soot oxidation and larger rates of heterogeneous conversion of NO2 to NO. With both single and multiple discharge pulse formats, the proportion of NOx removed, both in the presence and absence of soot, is about the same. The composition of the NOx depends on the soot. With 107 cm−3 of 40 nm soot particles, the final NOx was primarily NO2, whereas, with 109 cm−3 of 200 nm soot particles, the NOx was mainly NO.