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

The removal of NO x from diesel exhausts is being investigated using a variety of repetitively pulsed plasma sources. Soot particles influence NO x 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 NO x and soot oxidation. In the absence of soot, a series of discharge pulses results in increased conversion of NO to NO 2 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 NO 2 , followed by heterogeneous conversion of NO 2 to NO on the soot. With multiple pulses and soot, due to the larger gas phase density of NO 2 , there is an increased flux of NO 2 to the soot surface, resulting in increased soot oxidation and larger rates of heterogeneous conversion of NO 2 to NO. With both single and multiple discharge pulse formats, the proportion of NO x removed, both in the presence and absence of soot, is about the same. The composition of the NO x depends on the soot. With 10 7 cm −3 of 40 nm soot particles, the final NO x was primarily NO 2 , whereas, with 10 9 cm −3 of 200 nm soot particles, the NO x was mainly NO.