Influence of the injector setup on digital and continuous injection rate-shaping performance in diesel engine passenger cars

Abstract Injection continuous rate-shaping strategies, realized by means of state-of-the-art Common rail solenoid and direct acting piezoelectric injectors, have been tested at a dynamometer cell. NOx, soot, combustion noise and heat release rate data, pertaining to the two injector types, have been compared, based on a pilot-main injection calibration. The performance of the solenoid injectors resulted to be in line with that of the direct acting piezoelectric injectors. Digital and continuous rate-shaping strategies have then been investigated at a hydraulic rig in solenoid injectors. The cycle-to-cycle dispersion in the injected mass increases significantly in the closely-coupled injection regime, where the overall injected quantity raises up as the dwell time progressively reduces. However, as the dwell time is diminished to values well within the injection fusion zone, the cycle-to-cycle dispersion of the injected mass again improves and this confirms that is possible to implement effective continuous injection rate-shaping schedules also for the solenoid injectors. A previously developed one-dimensional model of a solenoid fuel injection system has been applied to perform parametric analyses on the solenoid injector setup: mechanical, electromagnetic and hydraulic parameters have been changed in order to investigate their effect on the closely-coupled injections. The objective is to provide design keys for realizing more efficient injection rate-shaping schedules in order to improve engine emissions, fuel consumption and combustion noise. Finally, the performance of two production solenoid injectors, which feature a different internal layout, has been compared in the short dwell time range and the experimental results have been successfully interpreted on the basis of the injector parametric analyses.