Combustion process management in common-rail DI diesel engines by multiple injection

The improvements of the solenoid injector and of the electronic control unit of the present Common-Rail injection system (C.R.) allow the use of multiple sequential injections. Thanks to this feature this advanced common-rail system is capable to perform up to five consecutive injections in one engine cycle thus improving control of the combustion process. In particular, in some operating conditions, the activation of a small injection after the main one allows the oxidation of the soot produced in the previous stages of the combustion process, without increasing nitrogen oxide emissions. This paper describes the experimental results obtained with the application of a prototype of this advanced common-rail system to a Fiat L4 1.9 JTD 8-valve 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 pollutants formation was also employed to interpret the trends observed in the experiments.