High Speed Shadowgraphy of Transparent Nozzles as an Evaluation Tool for In-Nozzle Cavitation Behavior of GDI Injectors

Abstract

Gasoline Direct Injection (GDI) systems have become a rapidly developing technology taking up a considerable and rapidly growing share in the Gasoline Engine market due to the thermodynamic advantages of direct injection. The process of spray formation and propagation from a fuel injector is very crucial in optimizing the air-fuel mixture of DI engines. Previous studies have shown that the presence of some cavitation in high-pressure fuel nozzles can lead to better atomization of the fluid. However, under some very specific circumstances, high levels of cavitation can also delay the atomization process; spray stabilization due to hydraulic flip is the most well-known example. Therefore, a better understanding of cavitation behavior is of vital importance for further optimization of next generation fuel injectors. In contrast to the abundance of investigations conducted on the inner flow and cavitation patterns of diesel injectors, corresponding in-depth research on the inner flow of gasoline direct-injection nozzles is still relatively scarce. In this study, the results of an experiment performed on real-size GDI injector nozzles made of acrylic glass are presented. The inner flow of the nozzle is visualized using a high-power pulsed laser, a long-distance microscope and a highspeed camera. The ambiguity of dark areas on the images, which may represent cavitation regions as well as ambient air drawn into the nozzle holes, is resolved by injecting the fuel both into a fuel or gas filled environment. In addition, the influence of backpressure on the transient flow characteristics of the internal flow is investigated. In good agreement with observations made in previous studies, higher backpressure levels decrease the amount of cavitation inside the nozzles. Due to the high temporal and spatial resolution of the experiment, the transient cavitation behavior during the opening, quasi-steady and closing phases of the injector needle motion can be analyzed. For example, it is found that cavitation patterns oscillate with a characteristic frequency that depends on the backpressure. The link between cavitation and air drawn into the nozzle at the beginning of injection is also revealed.

Modelling and prediction of cavitation erosion in GDi injectors operated with E100 fuel

“…The experiments of [22] with transparent glass GDi nozzles using differ-ent fuels relevant to spark ignition engines (including pure gasoline, E10 and E100 fuels), with injection temperatures ranging from 20 C o to 90 C o and back pressures ranging from 0.5 bar to 1 bar show that cavitation occurs at all the conditions tested. Further transparent nozzle experiments also confirm the presence of cavitation in GDi injectors [23,24,25]. Cavitation inside fuel injectors presents several distinct morphologies.…”

Experimental investigation of flow field and string cavitation inside a transparent real-size GDI nozzle

“…Therefore, the nozzle is extended along the injector axis. The nozzle holes are followed by one counterbore of similar dimension to those used in series GDI nozzles and then by multiple larger counterbores that facilitate the withdrawal of the fuel, as it is already presented in the previous study published by Mamaikin et al (2017). In this paper, the results of one nozzle hole are presented in detail.…”

“…1a. The test bench was already used in the previous work published by Mamaikin et al (2017), however, some modifications have been implemented to facilitate micro PIV measurements of the internal flow. Here, we briefly describe the main body and working principle of the test bench, placing an emphasis on the novel features.…”

“…Such studies on scaled models provide valuable insights into the fundamental in-nozzle flow behavior, however, the results often require plausibility checks to be transferred to practical flow conditions. Other experimental works performed the study of internal flow on real scale nozzles (Gilles-Birth et al 2005;Reid et al 2014;Mamaikin et al 2017). Such studies provide a good insight into the cavitation behavior at relevant injection conditions.…”

Measurement of needle and armature dynamics in a gasoline direct injector by high-speed neutron imaging

“…Armature lift can be measured by using the solenoid itself as a sensor by analysis of the voltage and current waveforms. 9 Needle lift at the top of the needle has been measured by laser Doppler vibrometry, 10 and lift and wobble (radial motion) of the check ball have been observed via optically transparent nozzles 11,12 and x-ray imaging. [13][14][15] However, it is not possible to make an entire injector optically transparent due to the high fuel pressure, and the thick metal cross section of the solenoid makes x-ray imaging challenging.…”