Advanced Measurement Techniques for Spray Investigations

The objective of this paper is to present recent advances at Onera in the spray diagnostic and simulation fields. In the context of the reduction of engine pollutant emissions, the optimization of fuel spray injection represents phenomena of great fundamental and practical interest and is an important feature in the design of new prototypes of turbojet injection devices. The physics of spray formation, transport, evaporation and combustion are not completely understood and the models must be improved to make better predictions of air fuel mixing inside combustion chambers. Onera, in cooperation with CNRS, has developed new optical diagnostics to obtain more detailed validation databases for validating numerical approaches.

New techniques are presented for characterizing the dispersed liquid phase in sprays in terms of droplet temperature, size and velocity. During the last few years, important work has been done on measuring the mean and local droplet temperature, by coupling Standard Rainbow Refractometry (SRR) and Laser Induced Fluorescence (LIF) for a monodisperse droplet stream [8]. Local characterizations of the discrete phase inside a polydisperse spray have also been carried out by the simultaneous use of the Global Rainbow Refractometry (GRR) method and the well known Phase Doppler Anemometry (PDA) technique. This paper describes the principle of these techniques and the different levels of application from basic configurations involving monodisperse droplet streams to polydisperse sprays in a high pressure and temperature environment. Experimental results are compared with the numerical ones for some simple configurations.