Effects of ultra-high injection pressure on penetration characteristics of diesel spray and a two-mode leading edge shock wave

• Experimental study of fuel spray up to ultra-high injection pressure was carried out.
• Ultra-high pressure was realized by a specially designed diaphragm rupture atomizer.
• Spray penetration data were compared against predictions of previous empirical equations.
• Two-mode leading edge shock waves connected by a junction point were investigated.

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.