Transient Injection Characteristics of a Pintle-Type Injector for Direct Injection of LPG

Spray characteristics of a pintle-type injector were studied by droplet velocity and diameter measurements and high-speed photography. A common rail fuel supply at 13MPa was used, and the injector was installed in an ambi­ent temperature chamber which was held at a pressure above (0.37MPa) and below (0.15MPa) the fuel vapor pres­sure. The entire injection event was analyzed as a time-average and also subdivided into three temporal intervals. The high-speed photographs showed a narrower cone angle during the quasi-steady spray period at the 0.37MPa chamber pressure compared to the 0.15MPa case. Except at the leading edge, during injection the spray was very dense and it was difficult to identify individual droplets or other features inside the spray. A vortex formed within 0.3 ms of the start of injection at the leading edge of the spray cone, and was most apparent for the 0.15MPa cham­ber pressure case. After injection stopped however, a fish-bone structure appeared at the higher chamber pressure and a web-like structure appeared in the lower chamber pressure case. The spray appeared to evaporate faster at 0.37MPa chamber pressure, even though this is above the fuel vapor pressure. Comparing the Sauter mean diameter (SMD) at 0.37MPa and 0.15MPa during the initial injection period, much wider spatial variation was seen at the higher chamber pressure. SMDs were similar at the spray edges (10 to 15µm) but nearly double in the interior. During the middle interval, the two peaks in SMD at 0.37MPa chamber pressure began to merge and the spray structure began to resemble that of a hole nozzle.