The improvements of the solenoid injector and of the electronic control unit of the present common rail (CR) injection system allow the use of multiple sequential injections. Thanks to this feature this advanced common rail system is capable of performing up to five consecutive injections in one engine cycle, thus improving control of the combustion process. In particular, at some operating conditions, activation of a small injection after the main one allows soot produced in the previous stages of the combustion process to be oxidized without increasing nitrogen oxide emissions. This paper describes the experimental results obtained with the application of a prototype of this advanced common rail system both to a Fiat 1.9 JTD eight-valve four-cylinder engine and to a single-cylinder prototype having the same combustion system and large optical access, allowing investigation of the injection and combustion processes. Multidimensional modelling of the combustion process and pollutant formation was also employed to interpret the trends observed in the experiments.

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