Quantitative measurements of nitric oxide in high-pressure (2–5 atm), swirl-stabilized spray flames via laser-induced fluorescence

Abstract

We report spatially resolved, linear laser-induced fluorescence (LIF) measurements of nitric oxide (NO) in preheated, high-pressure (2.09 to 5.35 atm), lean direct-injection (LDI) spray flames. The spray is produced by a hollow-cone, pressure-atomized nozzle supplied with liquid heptane. NO is excited via the Q 2(26.5) transition of the γ(0, 0) band. Detection is performed in a 2-nm region centered on the γ(0, 1) band. The major goal of this study is the validation and application of a complete LIF scheme by which quantitative NO concentrations can be measured in high-pressure LDI spray flames. Standard excitation and detection scans have been performed to assess possible interferences and to validate a nonresonant wavelength so as to subtract the influence of oxygen interferences in the NO detection window. NO is doped into the reactants and convected through the flame with no apparent destruction, thus allowing an NO fluorescence calibration to be taken inside the flame environment. The in situ calibration scheme is validated by comparisons with reference flames at high pressure. Quantitative radial NO profiles are presented at 2.09, 3.18, 4.27, and 5.35 atm and analyzed so as to better understand the operation of lean-direct injectors for gas turbine combustors. Downstream NO measurements in the LDI flames indicate an overall pressure scaling corresponding to P 0.74.