Experimental Study into Plasma-Assisted PM Removal for Diesel Engines

Plasma-assisted PM removal is examined in a packed-bed plasma system. This study focuses on the effect of plasma power, space velocity and exhaust gas composition on PM filtration. Experiments are done on an engine dynamometer with a VW 1.2l TDI engine. During these experiments, the airflow is throttled so large smoke levels are realized. Then, absolute filtration effects can better be observed. For relatively small space velocities, 90% filtration efficiency based on smoke measurements is determined at an energy density of 25 J/l (i.e. plasma power per exhaust gas volume flow). In the studied operating point, the filtration efficiency is not further increased for larger energy densities. Based on these results, we conclude that the available plasma power has to be increased for full flow experiments. In cases without airflow throttling, the plasma has no effect on PM filtration. Application of a 10 kV bias to enhance electrostatic precipitation is also seen to be ineffective. Future research into the effects of plasma on particle charge distribution has to give more insight in the observed processes at these relatively small particulate concentrations.

NO₂ production is also examined, since this gives an indication of maximal theoretical PM oxidation. For the case with maximal NO₂ production, we found a NO₂ energy efficiency of 0.12 kWh/g without adding hydrocarbons. Comparison with other experimental systems using hydrocarbon injection learns that the studied system is relatively efficient. The determined NO₂ production corresponds with maximal 0.89 kWh/g PM oxidation.