A study of pulsed corona discharge technology for NOx reduction from diesel engine exhaust is presented. The pulsed corona reactor consists of two coaxial cylinders used as electrodes of opposite polarities. The results are presented in terms of the cleanness (mass of NOx removed relative to its initial mass), and the efficiency (the energy required to theoretically dissociate 1 g of NOx relative to the energy actually needed). Experimental results show that for a pulsed corona, the polarity of the electrodes has no significant effect on the reactor performance. Cleanness was found to be independent of the engine load. The pulsed corona reactor design considers the most efficient means of energy transfer from pulse-forming capacitor to the discharge zone. It is shown experimentally that an external electrode of smaller diameter provides better NOx reduction. For a pulsed corona reactor, the residence time that provides the best performance must be sufficient to allow all the pollutant molecules to interact with the radicals produced by the corona discharge. The residence time is calculated for the pulsed corona reactor and experimentally confirmed to be the one that results in the best cleanness and efficiency of NOx removal. The empirical relations, based on working conditions, are obtained and provide a route for reactor design. (C) 2007 Elsevier Ltd. All rights reserved.