Soot Oxidation Studies in an Optical Diesel Engine Using Laser-Induced Incandescence and Extinction: The Effects of Injector Aging and Fuel Additive

Previous studies have shown that injector aging adversely affects the diesel engine spray formation and combustion. It has also been shown that the oxygenated fuel additive tripropylene glycol monomethyl ether (TPGME) can lower soot emissions. In this study, the effects of injector aging and TPGME on the late cycle oxidation of soot were investigated using laser diagnostic techniques in a light-duty optical diesel engine at two load conditions. The engine was equipped with a quartz piston with the same complex piston geometry as a production engine. Planar laser-induced incandescence (LII) was used to obtain semiquantitative in-cylinder two-dimensional (2D) soot volume fraction (f_v ) distributions using extinction measurements. The soot oxidation rate was estimated from the decay rate of the in-cylinder soot concentration for differently aged injectors and for cases with and without TPGME in the fuel. The aged injector produced higher soot concentrations than the new injector at both load conditions. The aged injector also showed higher soot oxidation rates than the new injector at the low load condition. TPGME resulted in lower soot concentrations at both load conditions and faster oxidation rates, especially at mid load conditions.