Multi-wavelength ultraviolet-visible extinction spectroscopy was applied to follow the evolution of fuel vapor injected by post-injection along the exhaust line of a common-rail turbocharged direct-injection diesel engine at moderate speed and load. The exhaust line was specifically designed and customized to allow the insertion of the optical access upstream of the Diesel Oxidation Catalyst.
During the experimental campaign, the engine was fuelled with commercial B5 fuel and a B30 v/v blend of RME and ultra low sulfur diesel, monitoring emissions upstream of the catalyst and exhaust gas temperature across the catalyst. Tests were performed at different engine operating conditions with particular attention to moderate speed and load.
The high temporal evolution of the UV-visible extinction measurements allowed to follow the evolution of the fuel vapor injected by post-injection during the transition from standard combustion mode to filter regeneration combustion mode, characterized by a higher amount of fuel injected into the exhaust line.
Results indicate that, in some engine operating conditions, the fuel vapor formed by post-injection does not completely contribute to the oxidation process over the catalyst since a negligible increase in temperature has been recorded across the catalyst.