Future exhaust gas limits for diesel-driven passenger cars will force the automotive industry to significantly improve the design of the vehicles respectively of the drive assemblies. Especially the contributions of soot and nitrogen oxide will be the main problems in the future. One possible solution could be the application of suitable exhaust gas aftertreatment systems, but since modern common rail injection systems deliver more degrees of freedom referring to the injection process, again the optimisation of the injection process could offer a possibility to meet the exhaust gas limits.
In this study, a passenger car common rail system, applied to an optically accessible transparent engine based on the AUDI V6 TDI engine, was investigated using a solenoid-driven and a piezo-driven injector, both equipped with the same injection nozzle. When using a pre-injection for the solenoid-driven injector, spatial coexistence of spray and flame could be observed over a large part of the engine cycle, because evaporation of the diesel fuel was too slow. The lack of oxygen in the areas where the flame could be detected enlarges the danger of higher soot formation as the conditions for an optimal fuel evaporation are deteriorated. Additionally, a significant wall contact of the spray cannot be avoided. The application of a piezo-driven injector showed that the fuel intake is now much faster but, due to stronger wave structures of the spray, which could be a result of better air entrainment, the tendency of developing a wall film is not higher. As a consequence, the fuel vaporises faster and both, building a wall film and spatial coexistence of fuel and flame, could be avoided when dimensioning these systems carefully.