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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]

In the present investigation, the transient developments of flow and cavitation within an injector’s nozzle during the oil drainage process have been studied by numerical method for a high-pressure common-rail DI diesel engine, both the variation regulations of macro parameters (indicating flow characteristics and cavitation characteristics) and the distribution manners of important physical fields (indicating the cavitation evolution in the micro) have been obtained and analyzed. The obtained numerical results indicate that, during the oil drainage process, both mass flow rate and flow coefficient monotonously increase with declining variation rates, both averaged flow velocity and averaged turbulent kinetic energy also monotonously increase; however, to the curve of TKE-needle lift, there exist certain points give abrupt increase. The difference in TKE curve compared to averaged flow velocity is mainly attributed to the sudden variation of cavitation. Based upon the numerical results, the cavitation bubble will not be formed until the needle lift has been raised to a certain position due to the lower flow velocity and the lack of low (even negative) pressure zones. As needle rises, the primary bubbles are formed near the lower corner after nozzle’s entrance; but as needle further rises, the positions at where bubbles are formed have been transferred to the upper corner and then being blow downwards orifice as the increase of flow velocity. [ABSTRACT FROM AUTHOR]