Nozzle tip wetting in gasoline direct injection injector and its link with nozzle internal flow

Abstract

Fuel film in the gasoline direct injection injector tip, or so-called nozzle tip wetting, has been found to be an important contributor of particle emissions. Attempts have been made to reduce the nozzle tip wetting by optimizing nozzle geometry designs. However, the inherent mechanism of the nozzle tip wetting formation and its link with nozzle internal flow is still unclear yet due to the lack of direct observations. To overcome this insufficiency, the nozzle internal flow and the formation process of the nozzle tip wetting were visualized in the real-scale aluminum nozzles using the X-ray phase-contrast technique. Results showed that the needle bouncing, injection pressure, and hole configuration affect the formation of the nozzle tip wetting, while the influence of needle bouncing is the most critical. A further study was conducted to examine the effect of nozzle counterbore diameter on the nozzle tip wetting. It was found that with an increase in counterbore diameter, the nozzle tip wetting slightly increased first and then decreased sharply after the counterbore diameter exceeded 0.40 mm. The mechanisms of the aforementioned phenomena were discussed in detail, which can contribute to the better understandings and control strategies of nozzle tip wetting.

Simulation of Liquid Film Spreading on Tip of Spray Injector

“…There are several factors in the generation of the fule adhesion. In addition to the fuel adhering to the nozzle tip by the reverse air flow shown in Figure 11, fuel films that are exposed to the nozzle tip by collisions of the spray plumes with the inner-wall surfaces at the nozzle outlets are also need to be reduced (Huang et al [1]). In order to reduce PM, it is necessary to reduce the amount of fuel film on the nozzle tip.…”

“…With GDI engines, fuel is directly injected into the combustion chamber by a fuel injector, so fuel adhesion on the walls is more likely to occur than with port-fuel-injection engines. Huang et al [1] investigated nozzle tip wetting in a GDI injector and its link with nozzle internal flow. Collision of the spray plume with the inner-wall surfaces at the nozzle outlets forms fuel films around the nozzles, which is one source of tip wetting.…”

Spray-wall interactions in direct-injection engines: An introductory overview

“…Fuel can reach the injector tip both from airborne droplets and directly as fuel exits the injector. The special issue paper by Huang et al 7 presents phase-contrast synchrotron x-ray imaging of needle motion, internal and exit nozzle flow, and nozzle tip wetting. The images and analysis show that needle bounce, injection pressure, and hole geometry (including counterbore diameter) all affect tip wetting, with fuel dripping during needle bounce as the most critical factor.…”

“…This special issue of International Journal of Engine Research (IJER) presents 11 papers that investigate spray-wall interactions (SWIs) and their effects at both fundamental and practical levels. These studies include numerical simulations 1–3 and measurements 4–8 of SWIs and fuel-film formation and dynamics, as well as measurements of fuel-film combustion and emissions processes. 9–11…”

Influence of Different Injector Structures on Tip Wetting by Visualization Method

“…Similarly, Oh et al reported that nozzle tip wetting could be reduced effectively by decreasing counterbore surface area [6]. In contrast, Huang et al observed that tip wetting slightly increases firstly and then decreases sharply along with the increase of counterbore diameter, and attributed it to both the needle bouncing and the change of hole configuration [7]. In order to clarify the specific relationship between the injector structure and tip wetting, some research was accomplished, and laser-induced fluorescence (LIF) was adopted to record the fuel film on the tip.…”