Isotope Shift/Planar Laser Induced Fluorescence Diagnostics for Examining Hydrogen-Methane Flames

Abstract

The chemical species in a mixture of hydrogen-hydrocarbon flame can be classified into two types according to their origins; one is produced from the hydrogen-air combustion reactions while the other from the hydrocarbon-air combustion reactions. For the separate visualization of the distributions of these two types, we have devised a new diagnostics tool for planar laser-induced fluorescence (PLIF) spectroscopy using isotope shift (herein called IS/PLIF spectroscopy). This diagnostics has been applied for separate visualization of the two-dimensional (2-D) distribution of the fluorescence intensity of the OH radicals produced from the CH4-O2-air combustion reactions and the 2-D distribution from the H2-O2-air combustion reactions in a CH4-H2-O2-air premixed flame. The selectively visualized 2-D distributions of OH radicals showed that the OH radicals produced from the H2-O2-air combustion reactions tend to exist upstream in the flame as compared to the OH radicals produced from the CH4-O2-air combustion reactions. For a quantitative comparison, we calculated the ratio of the 2-D integrated value of the OH fluorescence intensity produced from the CH4-O2-air combustion reactions to the 2-D value of all the OH fluorescence intensity in the CH4-H2-O2-air flame. This ratio is directly proportional to the number of moles of H atoms contained in CH4 in the CH4-H2 mixture.