The control of mixture formation by gasoline direct injection requires the continuous adaptation of the fuel spray characteristics in a broad range of load and speed.
This paper presents an experimental analysis of the main spray characteristics for a jet generated by a GDI system with high pressure modulation (Zwickau Ram Tuned). The experimental method is based on spray visualization by a laser sheet technique. The radiation of a Nd-Yag pulsed laser is scattered by the spray droplets laying on the lighted plane and collected by a CCD camera, being fed to a frame grabber. Time and space related structure can be analyzed in any cross section of interest, giving information about jet form and penetration length. In particular, a suitable elaboration (Presence Probability Imaging) of several image series, collected at different delay times after injection start, supplies information about the probability of presence in space of spray liquid fractions.
This approach was utilized for a complete characterization of the Ram Tuned injection system, operated in a wide range of settings (in terms of initial pressure, acceleration time, injector opening pressure and needle lift).
A comparison of the spray obtained with a poppet valve nozzle and with a two-hole nozzle for the same pressure wave input was also performed. The results are comparable with previous complementary LDA measures and confirm the tendencies obtained by numerical simulation of the process by Fluent code.