Direct Chemical Reduction of NOx in Diesel Exhaust

Early research in the application of nonthermal plasma technology to reduce NOx in combustion emissions established that the chemistry resulting from the direct excitation of exhaust gas streams is dominated by oxidation of NO to NO₂ and nitric acid, undesirable end products for mobile systems. An alternative to direct plasma generation in diesel exhaust has now been demonstrated to shift this exhaust NOx chemistry from oxidation toward reduction to nitrogen and oxygen. The new approach reacts NO with atomic nitrogen injected into the exhaust stream through multiple electrically excited high-speed nitrogen jets. Chemical reduction of more than half of the NO in diesel exhaust has so far been demonstrated, with only minimal production of N₂O. The technology functions well in the sooty and wet conditions characteristic of diesel exhaust. A system is presently being built for testing and evaluation on exhaust slipstreams at a Caterpillar Inc. test facility.