Multi-Schlieren 3D-CT Measurements of Instantaneous Equivalence Ratio Distributions of a Premixed Gas Field Based on Modified Refractive Index

Abstract

In quantitative measurements and investigations, "equivalence ratio" and "refractive index" are the most significant parameters in combustion flow fields. Experimental and analytical studies were performed to understand the relation between equivalence ratio and refractive index in flow fields. A "universal relationship" between the refractive index of a premixed gas of fuel and air and its equivalence ratio has been established in this study. Through this relationship, we can calculate the equivalence ratio of any premixed gas (except those of light fuels) from its refractive index using a unique coefficient. The uniqueness of the relation coefficient enables us to obtain the equivalence ratio of even a multi-fuel premixed gas from its refractive index. In this study, the novel relationship is applied to a non-scanning 3D-CT (computerized tomography) technique using a multi(20)-directional quantitative schlieren optical system with a flashlight source. Instantaneous equivalence ratio distributions of a dual-fuel premixed gas flow with two jets of ethanol/air and propane/air mixtures are measured by CT-reconstruction. Good agreement was observed between the CT-reconstructed data and the proposed comprehensive relation.