It has been widely recognized that the spread of diesel vehicles is expected to grow significantly around the world, even in countries like the United States where the current penetration is not yet comparable to that of gasoline engines. However, future emission standards envisaged (EURO V) for diesel vehicles indicate that, together with the results obtained in the future by improving the technology of the engine and the quality of the fuel, it will be necessary to resort to the use of post-treatment systems. The severity of the EURO V rules (limits even lower than Euro IV for particulate and NOx, with specific reference to the size distribution of particulate matter) require new solutions based on catalytic traps.
The main objective of this project was to expand and deepen the knowledge of post treatment catalytic systems assisted by microwave and cold plasma in order to develop a technology able to enforce the EURO V legislation.
The objective had to be achieved through two coordinated approaches:
i) optimization of the formulation of the catalyst and support ‘s active phases, to either exploit the selective heating of the particulate by the microwave, thus reducing the power required for the regeneration of the filter, or the oxidizing ability of the NOx together or without cold plasma;
ii) control, under realistic conditions of the performance of the systems proposed for the post-treatment (structured catalytic filters, testing of a diesel engine common rail’s exhaust).
The regeneration systems of catalytic filters based on cold plasma and microwave appeared to be very suitable for future applications, both to reduce the additional consumption of fuel, as well as to overcome the problems related to the not controlled regeneration.
Microwave irradiation as a technique for active regeneration of filters for diesel particulate had been revived recently with a microwave-regenerated Silicon carbide (SiC) fiber filter able to convert the electromagnetic energy into thermal energy with an efficiency of about 100%. The tests on the engine showed high efficiencies of regeneration with a reduced consumption of additional fuel.
Furthermore, it was shown how the coupling of catalytic technologies with techniques that make use of cold plasma can result in a considerable increase in efficiency for pollutants reduction (NOx and particulate matter) present in exhaust gases from diesel engines.
The plasma becomes chemically reactive thanks to the interaction between the electrons and the gas molecules which causes the dissociation of the molecules into radicals. Such reactivity can be exploited to induce chemical reactions at low temperature (non-thermal plasma) which would allow the destruction of the pollutants in the exhaust gases. The process has a high efficiency, as can be enabled a wide range of chemical reactions with a low input of energy.