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Modern diesel engines employ higher injection pressure in the common-rail injection system that utilizes high-speed fuel jet to achieve rapid fuel-air mixing for spray atomization improvement. However, the spray characteristics under super high pressure are not well understood. To provide more information on spray characteristics, both the macro- and micro-characteristics of spray have been investigated under super high pressures (up to 300 MPa) via an experimental method. The spray penetration and spray cone angle were measured using a high speed camera and the microscopic characteristic of Sauter mean diameter (SMD) was obtained via Malvern Spray Tec to analyze the influence of super high injection pressure on diesel spray atomization. Induced shock waves were captured using a Schlieren system when the spray tip velocity was greater than the local sound velocity accompanied by diesel spray. The results obtained show that higher injection pressures lead to larger spray velocities and a smaller shock wave angle if it exists, with connection between spray and shock waves, and generates a smaller SMD with less decreasing amplitude. Additionally, two different types of leading shock waves—bow and oblique shock wave appeared sequentially with increasing injection pressure. [ABSTRACT FROM AUTHOR]

An experimental study was carried out to investigate the effects of ultra-high injection pressure on the penetration characteristics of diesel sprays and leading edge shock waves generated around the sprays that propagate in two modes. The visualization of the spray field using high-speed photography was carried out in the ultra-high pressure fuel injection system equipped with a diaphragm rupture atomizer. Schlieren imaging was used to visualize the shock waves. The experimental results indicated that the spray jet had stronger penetration momentum at higher pressures, but the penetration spacing diminished with increasing pressure between 200 MPa and 400 MPa (i.e., at ultra-high injection pressure). Furthermore, the penetration model proposed by Hiroyasu and Arai retained its predictive power at ultra-high pressures. Regarding the propagation behavior of the induced leading edge shock wave, two modes were observed: that of “spherical” and “oblique” shock waves—these can be characterized by different generation mechanisms and velocity distributions. Additionally, observing the effects of injection pressure on the penetration characteristics of the two modes yielded insight into the duration of the rapid ascent of spherical velocity and the correlations between the spray front angle θ , oblique shock angle β , and spray tip Mach number M in the oblique shock. [ABSTRACT FROM AUTHOR]

The phenomenon of shock waves can be commonly seen in fuel spray under ultra-high injection pressure conditions, where the spray jet penetrates at speeds greater than Mach 1. This paper focuses on the induction of shock waves and their propagation characteristics generated by a supersonic fuel jet at 400 MPa, and simultaneously considers the impact of jet atomization. A specially designed atomizer, utilizing diaphragm rupture, was adopted to replace the traditional electronic valves fuel system to meet the ultra-high injection pressure. Visualization of the spray field by using a high-speed camera was conducted, and a Schlieren apparatus was equipped for shock capturing based on a variable environmental density distribution. The experimental results indicated that the leading edge shock wave shows two forms in the early stage, and each penetrates in a unique way. Along with the spray development, multiple expansion waves were sequentially generated, followed by the leading shock wave. The evolution of wave velocity over time was calculated from the penetration results, and the results showed that the velocity first increased rapidly and then slowly decreased as a result of the effect of air resistance, with a gradual tendency of decreasing for the four peak velocities of the intensity weakened waves. In addition, the spray convex flow path had an inhibitive effect on the deceleration of the first expansion wave. These results give an insight into diesel spray and propagation process of induced shock waves at an under ultra-high injection pressure of 400 MPa. [ABSTRACT FROM AUTHOR]