Determination of density and concentration from fluorescent images of a gas flow

TL;DR

This paper presents a fluorescent image analysis method to simultaneously measure species concentration and density in gas flows, demonstrated on under-expanded sonic jets, with results validated against existing experimental and numerical data.

Contribution

A novel fluorescent imaging technique that extracts both species concentration and density from spectral superposition in gas flows.

Findings

Density distribution along jet axis is self-similar.

Method accurately measures concentration and density in gas jets.

Results agree with previous experimental and numerical studies.

Abstract

A fluorescent image analysis procedure to determine the distribution of species concentration and density in a gas flow is proposed. The fluorescent emission is due to the excitation of atoms/molecules of a gas that is intercepted by an electron blade. The intensity of the fluorescent light is proportional to the local number density of the gas. When the gas flow is a mixture of different species, this proportionality can be exploited to extract the contribution associated to the species from the spectral superposition acquired by a digital camera. This yields a method that simultaneously reveals species concentrations and mass density of the mixture. The procedure is applied to two under-expanded sonic jets discharged into a different gas ambient - Helium into Argon and Argon into Helium - to measure the concentration and density distribution along the jet axis and across it. A comparison with experimental and numerical results obtained by other authors when observing under-expanded jets at different Mach numbers is made with the density distribution along the axis of the jet. This density distribution appears to be self-similar.