Piloted Liquid Spray Flames: A Numerical and Experimental Study

摘要

Liquid-fuel spray flames are the primary mode of energy conversion in many high-power-density practical combustion devices. As compared to gaseous fuels, the phase change in liquid-fuel spray flames complicates the environment for laser-based combustion diagnostics and formulating predictive computational models. In this work, we present in-situ, non-intrusive measurement strategies and predictive models for combustion and carbon monoxide (CO) formation in piloted liquid-methanol spray flames. Resolving CO is essential to understand the incomplete oxidation of liquid hydrocarbon fuels and subsequent soot formation. A modified, flat-flame McKenna burner fitted with a direct-injection high-efficiency nebulizer (DIHEN) is used to produce piloted liquid-methanol spray flames. Hydroxyl (OH) planar laser-induced fluorescence (PLIF) is used for characterizing the reaction zones and temperature profiles of liquid-spray flames and two-dimensional (2D) images of CO are obtained via two-photon laser-induced fluorescence (TPLIF) using ultrashort, femtosecond-duration (fs) laser pulses. A three-dimensional (3D) computational model comprised of compressible continuous gas phase using unsteady Reynolds-averaged Navier-Stokes (URANS) in conjunction with two-way coupled Eulerian-Lagrangian spray modeling approach and partially-stirred reactor combustion model has been adapted to the modified McKenna burner. The computational model predicts the general trends of OH, temperature and CO profiles well at certain heights above the burner surface. Limitations of experimental measurements and strategies for improved model predictions pertaining to distributions of droplet sizes, pilot flame temperature, and the coflow temperature are discussed.