Macroscopic Properties of Hollow Cone Spray Using an Outwardly Opening Piezoelectric Injector in GCI Engine

摘要

Fuel mixture formation and spray characteristics are crucial for the advancement of Gasoline Compression Ignition (GCI) engine. For investigations of spray characteristics, a high-pressure high-temperature spray chamber with constant volume has been designed, tested and commissioned at CCRC, KAUST. Back light illumination technique has been applied to investigate the macroscopic spray properties of an outwardly opening piezoelec- tric injector. Three parameters including injection pressure, ambient pressure, and ambient temperature have been involved. A total of 18 combinations of experimental conditions were tested under non-reactive conditions.udThrough qualitative analysis of spray morphology under different operating conditions, an apparent distinction of spray morphology has been noticed. Spray morphology and propagation have shown strong dependencies on ambient pressure and ambient tempera- ture while injection pressure has a negligible effect on spray shape. Increasingly compact and bushier spray patterns were observed in the cases of high ambient pressure due to in- creasing aerodynamic drag force on spray boundary. It should also be noted that ambient temperature plays a fairly important role in fuel evaporation rate. At 200 °C, oscillating and considerably short spray shape was produced. Also, circumferential ring-like vortices and distinctive string-like structures have been identified for the fuel spray exiting this hollow cone injector. It has been observed that high ambient pressure conditions (Pamb = 4 bar andud10.5 bar) are favorable to the vortices generation, which has also been reported in previous literature.udThe quantitative description of macroscopic spray properties reveals that ambient pres- sure and ambient temperature are found to be the most influential parameters on liquid penetration length. The rise of ambient pressure results in considerably shorter liquid pen- etration length. Ambient temperature also appears to be a very effective factor of reducing penetration length. Injection pressure contributes to a notable increase of liquid penetra- tion length under ambient pressure of 1 atm. However, the influence of injection pressure is substantially reduced under ambient pressures of 4 bar and 10.5 bar, which indicates that ambient pressure exerts much stronger influence than injection pressure on liquid penetra- tion length.udFurthermore, it has been revealed that the increase of injection pressure and ambient pressure are the predominant sources contributing to the enlargement of spray cone angle. The effect of injection pressure on spray cone angle has been amplified by the increase of ambient pressure. With increasing ambient pressure, the penetration of injected fuel tends to propagate axially in a much slower manner that leads to wider fuel distribution in the radial direction. Ambient temperature exerts a similar influence on spray cone angle as on liquid penetration length. The spray cone angle experiences a noticeable decline when ambient gas is increased to 200 °C.