Impact of Non-Thermal Plasma on Particulate Emissions in Application in a Diesel Engine Exhaust Duct

Particulates and nitrogen oxides comprise the main emission components of the Diesel combustion and therefore are subject to exhaust emission legislation. Yet, with more stringent emission standards and test-procedures, such as in passenger vehicle applications, resulting exhaust gas after-treatment systems are complex and costly. Hence, new technologies for emission control have to be explored. The application of non-thermal plasma (NTP) as a means to perform exhaust gas after-treatment is one such promising technology. One way to generate a NTP is by a corona high-frequency discharge. Apart from few other publications dealing with NTP exhaust gas aftertreatment where a NTP was generated via dielectric barrier discharges (DBD), the experiments in this publication were conducted on an operated series-production Diesel engine with an industrial pilot-type corona ignition system. Originally developed as an alternative for a spark-plug system in SI engines its attributed properties, such as large penetrated volume and high radical concentration, may also be utilized in the exhaust gas stream as it has been done in this publication. To investigate the effects of a corona discharge on Diesel engine emissions, four igniters were integrated in the exhaust duct of a CRDI 2.0 liter engine equipped with DPF. The impact on particle number, size distribution as well as on nitrogen oxides has been studied for various operational parameters of the corona system. The particle number was measured downstream of the DPF to observe the level of improvement for remaining unfiltered nanoparticles. In this first series of tests, a reduction in particle number of up to 10 % was achieved depending on engine load. Particle size distribution was measured upstream of the DPF. In this case, the highest reduction of 10 % was observed in the mid-range particle size of about 60 nm. No increase in other particulate size ranges has been observed.