The effect of cavitation on the estimation of fuel injection rates based on momentum flux measurements

Artikel i vetenskaplig tidskrift, 2019

A study was conducted to determine how geometry-induced cavitation affects the reliability of injection rate estimates based on momentum flux measurements. Experiments were performed with two hydro-grinding diesel injector nozzles (Do = 190 µm), one having a cylindrical nozzle orifice that has a strong tendency to induce cavitation, and the other having a convergent nozzle orifice that tends to suppress cavitation. In addition, near-field microscopic images were captured to investigate the influence of cavitation on the liquid jet at the nozzle exit. The momentum flux measurements and near-field imaging were conducted at ambient pressure, using injection pressures of up to 2500 bar. When estimating the injection rate based on momentum flux measurements, failure to account for cavitation caused the integrated injection rate to be overestimated around 9% for the cavitating (cylindrical) nozzle but not for the non-cavitating (convergent) nozzle. We therefore recommend that cavitation should be accounted for when estimating injection rates for cavitating nozzles but not for non-cavitating nozzles. Further, we show that the tendency of a given nozzle orifice to induce cavitation can be evaluated by measuring the nozzle's momentum flux under the assumption of zero cavitation and then comparing the estimated mass of injected fuel to the weighed mass.