Boot injection dynamics and parametrical analysis of boot shaped injections in low-temperature combustion diesel engines for the optimization of pollutant emissions and combustion noise

Innovative direct-acting piezoelectric injectors that are capable of flexible injection rate shaping have been tested at a hydraulic test rig. The effect of boot injection dynamics on the injector hydraulic performance was analyzed on the basis of the measured injected flow-rate time histories. The injectors were then installed on a Euro 5 low-compression ratio diesel engine, fueled with conventional diesel oil and managed with a late PCCI type combustion. The engine has been tested at a dynamometer cell, and a parametric analysis has been performed considering both the charging time and the holding time of the boot injection in order to assess the impact of their variations on engine-out emissions, combustion noise and brake specific fuel consumption. Explanations of the cause-and-effect relationships between the boot injection parameters and the engine performance have been provided: a three-zone combustion diagnostic tool has been applied to support the experimental investigation. The tests at the engine dynamometer cell refer to the low-to-medium load and speed area of the engine NEDC zone, since the tests were focused on the exploitation of the boot injection in late PCCI combustion strategies.