Real time control of GDI fuel injection during balistic operation mode

Gasoline direct injection (GDI) combustion with un-throttled lean stratified operation allows to reduce engine toxic emissions and achieve significant benefits in terms of fuel consumption. However, use of gasoline stratified charges can lead to several problems, such as a high cycle-to-cycle variability and increased particle emissions. Use of multiple injection strategies allows to mitigate these problems, but it requires the injection of small fuel amounts forcing the traditional solenoid injectors to work in their "ballistic" region, where the correlation between coil energizing time and injected fuel amount becomes highly not linear. In the present work a closed-loop control system able to manage the delivery of small quantities of fuel has been introduced. The control system is based on a particular feature found on the coil voltage command signal during the de-energizing phase. On the basis of this feature, the injector needle closing time and then, in turn, the actual amount of fuel injected can be calculated. Results showed that the proposed control system, through a proper management of ballistic injections, has the potential to increase the minimum fuel injection capabilities of GDI solenoid injectors.