Combined “Fluorescence” LDV (FLDV) and PDA Technique for Non-ambiguous Two Phase Measurements Inside the Spray of a SI-Engine

Abstract

Laser velocimetry measurements in the vicinity of reflecting surfaces are still a major problem in many fluid mechanical applications such as measuring close to walls or wall film surfaces, respectively. Moreover, in any kind of two phase flow an unambiguous separation of the gas and the liquid phase is of particular interest. Commonly used techniques like Phase Doppler Analyzers (PDA) with size discrimination are limited to two phase flows where the smallest particle of the dispersed phase is significantly larger than the seeding particles. This condition can rarely be fulfilled in technically relevant spray/air systems for instance in automobile engines or gas turbines. One of the most promising approaches to overcome this problem is a correct phase discrimination using fluorescent tracer particles for the gas phase. In this paper different laser based velocimeters have been compared using the spray of a gasoline injection nozzle as a typical example. The working principle of the “fluorescence” LDV (FLDV) will be explained in detail. Moreover, the quality of the fluorescence signals and of the standard bursts received from Mie-scattering particles will be compared. Finally, the capabilities of combined FLDV and PDA measurements inside the spray of a SI-engine at unsteady conditions will be presented. The pros and cons of this technique will be discussed against the background of discriminatory two phase PIV measurements applied to the same spray.