Relationship between NOx formation in diesel exhaust and CN band spectra in diesel combustion flames

Abstract

We inserted an optical fiber into the combustion chamber of a DI engine and investigated the diesel flame spectra. The engine, with a water spray device attached in the intake pipe, was operated under various ignition timings, and the relationships among the intensity of CN band spectra, NOx concentration in the diesel exhaust and the flame temperature were investigated. As a result, a correlation was found between CN band spectra and NOx concentration. From this correlation, we confirmed that the diesel exhaust contains not only NOx generated by the “Zeldvich mechanism”, but also “prompt NOx”. We also confirmed that to reduce “prompt NOx”, it is not effective to retard the ignition, but it is effective to spray water into the combustion chamber in high-load operations. © 1995, The Japan Society of Mechanical Engineers. All rights reserved.