Fundamental Limits on Gas-Phase Chemical Reduction of NOx in a Plasma

This paper examines the gas-phase chemical reduction of NOx. It is shown that under the best conditions, the plasma can chemically reduce 1.6 grams of NOx per brake-horsepower-hour when 5% of the engine output energy is delivered to the plasma. This NOx reduction efficiency is a fundamental limit that cannot be exceeded in the absence of heterogeneous reactions or chemical additives. Higher NOx removal efficiencies would suggest reactions of plasma oxidation products (such as NO2 or nitric acid) on surfaces or particulates.