NO _x Formation and Models

Abstract

The principal nitrogen oxides emitted from spark ignition and diesel engines are nitric oxide ( NO ), nitrogen dioxide ( NO 2 ), collectively referred to as NO x , and nitrous oxide ( N 2 O ). Accurate prediction of nitrogen oxide emissions from these engines requires knowledge of the important gas‐phase reaction pathways involving nitrogen species and the rate parameters for these pathways. In this chapter, the current state of understanding of the gas‐phase reaction mechanisms for nitrogen oxide chemistry in combustion, including the mechanisms for NO formation from molecular nitrogen in the air and from nitrogen present in fuel additives and the mechanism for NO removal via a gas‐phase reaction process termed reburning is discussed. In many combustion processes, these formation and removal pathways are coupled. In addition, the reaction mechanisms for the formation and removal of NO 2 and N 2 O are described. The relative importance of the different NO formation and removal pathways in different combustion environments is presented.