Nox reduction from biodiesel exhaust by plasma induced ozone injection supported by lignite waste adsorption

This paper explores the technique of ozone injection to induce reactions leading to NO conversion in a diesel engine exhaust and subsequent adsorption by lignite ash, an industrial waste from lignite coal fired power plants. Experimental investigations were carried out using a diesel engine fuelled by biodiesel, prepared from pongamia pinnata, a native Indian plant. Ozone is produced from dry air in a Dielectric Barrier Discharge (DBD) reactor by the application of high voltage. The choice of the high voltage was made after a comparative study between high frequency AC and unipolar repetitive pulse source, with the latter consuming lesser power for given ozone production. By injecting ozone, the higher composition of NO in biodiesel exhaust gets oxidized to higher oxides of nitrogen in general and NO2 in particular. This NO2 can be adsorbed in the lignite fly ash pellets as successfully demonstrated in this paper. This combined ozone injection-lignite ash adsorption technique has resulted in an overall removal efficiency of oxides of nitrogen (NOx) as high as 95% even under loaded conditions. A comparison has also been made between the ozone injection technique and direct plasma treatment of exhaust for NOx removal.