Understanding of closely spaced split injections of an outward-opening piezoelectric gasoline injector by large eddy simulations

Abstract

Copyright © 2021 The Authors. The outward-opening piezoelectric injectors are capable to achieve precise and flexible controls of the fuel injection rate and duration with rapid opening and closing for split or multiple injections, which can minimise wall wetting and deposit formation in Gasoline Direct Injection (GDI) engines. However, experimental studies have shown that narrowly spaced split injections with short dwell time can increase cycle-to-cycle variation and emissions. In this study, large eddy simulations (LES) of an outward-opening piezoelectric gasoline injector were performed to understand the interactions between split injections and their impact on the flow fields, fuel/air mixing and transportation. The simulations were performed in a constant volume vessel and validated with experimental data. The results at both 1 bar and 10 bar backpressures showed that the droplets, fuel vapor and flow fields distributions were significantly affected by split injections when short dwells (0.6 ms and 1 ms) were applied. In particular, the fuel vapor distribution at recirculation zones of the spray where the spark plug is normally positioned was significantly changed after the second injection, compared to that of single injection, implying potential impact on the ignition stability.