Flash boiling spray has been regarded as a promising fuel injection technology. Many investigations have been focused on spray physics and mechanisms of flash boiling spray, but information on flash boiling of alcohols in GDI engines is very limited. In this paper, the spray characteristics, flame propagation, combustion analysis, and PN emissions of butanol isomers under flash boiling spray have been studied. A constant volume chamber with a high-speed camera used to investigate the flash boiling spray of butanol isomers and gasoline surrogate blends. The flash boiling spray was tested at 180 °C and compared to subcooled spray at 25 °C. The tested gasoline surrogates are primary reference fuel (PRF) and toluene primary reference fuel (TPRF). The flash boiling leads to the collapse of the spray six plumes into a single extended spray plume with longer spray penetration compared to subcooled injection. The spray study then extended to study the effects of flash boiling injection on flame development and PN emissions of the GDI optical engine. The results reveal that flash boiling injection leads to lower apparent flame speed and flame area compared to subcooled injection due to the lean-like burn condition, and yellow flame spots are diminished. The peak in-cylinder pressure and apparent heat release rate are reduced with longer ignition delay when the flash boiling injection is applied. The flame lasted longer under flash boiling conditions with improved late combustion phase, which results in higher heat released. The PN emissions reduced with flash boiling spray compared to subcooled conditions. |
