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This paper reports efficient treatment of diesel emission with transient, non-equilibrium plasma created by a pulsed corona discharge. The transient plasma (∼50 ns) is found to reduce NOx emission in a flow of 1-10 liters/ second with energy cost ≤10-20 eV/molecule, corresponding to a fraction of source power of ∼5%. The efficiency of NOx reduction is a complex function of parameters that include pulse width, pulse polarity, current density, repetition rate, and reactor design. It was found that best efficiencies are correlated with a low current density (0.2A/cm2) and high repetition rate (1kHz) under high flow rate. Careful optimization of all these parameters is required to reach cost effective NOx reduction.

Increasing environmental awareness and regulatory pressure have motivated investigations into energy efficient methods to remove oxides of nitrogen (NOx) from diesel exhaust. Past emission requirements have been achieved by modifying the engine combustion parameters. However, engine modifications alone are not sufficient to meet the proposed 2004 EPA regulations for heavy duty diesel powered trucks. Some form of post combustion control is necessary. Conventional catalyst technologies, such as three-way automotive catalysts are ineffective under high oxygen levels. The use of non-thermal plasmas offers the potential to selectively reduce NOx in such high oxygen exhausts without the need for supplemental scavengers or additives. Plasmas produce energetic electrons which collide with the background gas molecules leading to the formation of a variety of new species including ions, metastable species, atoms and free radicals.