Particulate matter emission reduction from marine diesel engines by electrohydrodynamic methods

Particulate matter (PM) and gaseous compounds (SO2, NOx, VOC) emitted by diesel engines causes serious global environmental problems and health impact. Despite numerous evidences about the harmfulness of diesel particles, the PM emission by diesel engines used by ships, cars, agricultural machines, or power generators is still unregulated, and the efficient removal of PM from diesel exhausts is still the major technological challenge. In order to comply with the International Maritime Organization regulation, the NOx emission is reduced by using selected catalytic reactor, and sulphur oxide emission has been reduced by using fuels of low sulphur content. However, both of those measures cannot be used for the reduction of PM emission produced during combustion of marine fuels. The lack of appropriate regulations results from insufficiently developed technology, which could remove those particles from exhaust gases. Conventional scrubbers currently available on the market remove only sulphur oxide with required collection efficiency, but the collection efficiency for PM2.5 is below 50%. The article discusses the technical means used for the removal of PM from marine diesel engines via applying electrohydrodynamic methods, in particular electrostatic agglomeration, as a method of nanoparticles coagulation to larger agglomerates, which could operate in two-stage electrostatic precipitation systems, and electrostatic scrubbers, which remove particles by electrically charged water droplets. The experimental results were obtained for a 2-stroke 73 kW diesel engine fuelled with marine gas oil (MGO). The agglomerator allowed increasing the collection efficiency from diesel exhausts for PM2.5 particles by about 12%, compared to electrostatic precipitator operating without agglomerator, and the total mass collection efficiency was above 74%. The collection efficiency of electrostatic scrubber was higher than 95wt.%. The advantage of using the electrostatic scrubber is that it can also reduce the SO2 emission by more than 90%, when HFO is used.