Experimental characterization of outlet flow for different diesel nozzle geometries

Three diesel injector nozzles with different geometries have been characterized under cavitating and non-cavitating conditions using injection rate measurements and momentum flux measurements. Apart from the expected choking of the mass flow, also an important increase in velocity at the exit of the nozzles orifice is observed, when cavitation appears.

The analysis of the results using three original characteristic parameters of the flow at the exit of the nozzle orifice enables us to resume the global information of a specific nozzle in terms of mass flow rate, momentum flux, flow velocity and density at the exit for the whole range of the engine's injection pressures and backpressures. Each nozzle is defined by only three characteristic constants. This has the undeniable practical aspect for comparing different nozzles. Furthermore by analyzing the results using our empirical model we are able to give a direct explanation for the influence of the average flow density at the exit of the orifice, explaining the increase in exit velocity and mass flow ‘collapse’ when cavitation appears.

The developed semi empirical model therefore is a useful tool for comparing nozzles, for 3-D modeling purposes and also for explaining differences in spray behavior and combustion.