Effect of the nozzle holder on injected fuel temperature for experimental test rigs and its influence on diesel sprays

Abstract

One of the test boundary conditions whose control is necessary for both experimental and numerical studies about the automotive engines research field is the temperature of the fuel inside the injector body during the injection. However, it is a difficult parameter to be directly measured in a non-intrusive way due to the injector architecture and the nature of the standard experiments that are done to characterize sprays. An experimental analysis is performed in this work employing a continuous flow test chamber, normally used in the optical diagnosis of diesel sprays, in order to compare and characterize two different designs for the nozzle holder of the test rig. The first one consisted in an aluminum holder that coats the nozzle until its tip, while the second one is made of steel and only supports the nozzle without covering it from the environment. The employed methodology was to set the test rig at a wide range of thermodynamic conditions inside the vessel such as ambient temperature and density and also the coolant temperature at the outlet of the injector casing for both cooling pieces. In this case, a dummy injector provided with a thermocouple was used to measure the tip temperature. In this way, correlations are obtained to estimate the injector body temperature out of the measurement points. Further experiments with a real single-hole diesel injector, controlling its tip temperature according to the previous results, are also discussed in this article in order to analyze the effect of this parameter on the spray evaporation process. Liquid length at inert conditions and both ignition delay and lift-off length at reactive ones were measured employing the same test vessel. All those parameters showed to be shortened with an increment of injected fuel temperature, and the lower the ambient temperature, the stronger this influence is.