Study on plasma treatment of NOX in engine exhaust gas

Rising environmental concerns and increasingly stringent legislation ask for new technological solutions to lower emissions and reach cleaner combustion processes. In densely populated areas, transportation, especially road transportation, has a direct impact on air quality, and consequently on health of the residents: in the last two decades, since the first EURO I standard was introduced, pollutants emissions for all the categories subjected to legislation consistently decreased, however, in order to avoid deleterious effects on human health and environment generally, a need to monitor unregulated pollutants and continuously reduce the emission of those already subjected to regulations is indispensable. Among other pollutants, NOx, for which transportation sources represent 49\% of the total emissions, are toxic chemicals responsible for the formation of ground-level ozone and particulate, and together with sulfur dioxide are the major contributors to acid rain. NOx are produced by all kind of IC engines, however their formation path is particularly favored in diesel engines, in which the excess of oxygen and higher temperatures lead to a substantial increase of NOx compared to other engine types. The fact that diesel engines are considered superior by other factors, their efficiency, reliability, and variety of applications, made the possibility of reducing NOx emission an active area of research. The utilization of non-thermal plasma technology has been investigated in order to obtain the conversion of nitric oxide into nitrogen dioxide, a pollutant more effectively treated by modern catalyst reactors. First, tests were carried out in order to identify a suitable form of plasma generation, and a dielectric barrier discharge plasma reactor was realized. The energy efficiency evaluation required a proper, more accurate, power measurement method. The initial tests were conducted employing artificial gasses, gradually increasing the number of the mixture components in order to identify the role played by each of them in the NOx treatment. During a second round of tests the gas exhausts from a 50cc scooter engine was sampled and flowed through the reactor; the effect of the presence of other chemicals, absent in the artificial gas mixture was found. A numerical simulation of plasma induced chemistry was developed in order to highlight the principal mechanisms underlying the phenomena of interest.