Multiwavelength ultraviolet absorption spectroscopy of NO and OH radical concentration applied to a high-swirl Diesel-like system

Ultraviolet absorption measurements were carried out in an optical research engine by exploiting the emitted plasma kernel of laser-induced breakdown. Temporal evolution and spatial distribution of OH radical and NO absolute concentrations were evaluated by a numerical procedure for retrieving optical data. Spectral measurements were made in an optically accessible external combustion chamber obtained by modifying a single cylinder, four-stroke diesel engine. The experiments were performed using a commercial diesel fuel at two engine speeds varying the ignition delay and fixing the injected fuel amount. In-chamber NO concentrations for each engine operating condition were correlated with those measured at the exhaust by a conventional method.