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. (C) 2017 Published by Elsevier Ltd.