Coupling effects of physical and chemical properties on jet fuel spray flame blowout

Abstract

This work uses an annular co-flow spray burner as a laboratory test method for evaluating one of the important jet fuel figures of merit, namely lean blowout (LBO), and investigates the coupling of physical and chemical properties affecting this phenomenon. Previous work has shown that relative trends in LBO from different fuels in a real gas turbine are well reflected in this burner setup. Representative characteristics for fuel heat of combustion, volatility, atomization, and pressure are used to produce correlations predicting the LBO for this spray burner, thus these characteristics are considered important toward the prediction of LBO in real gas turbine combustors. The results of this testing are compared to general relations for spray flames as published in prior literature; it is found that equivalence ratio at LBO is positively correlated to fuel flow rates and effective evaporation, and inversely correlated to combustion pressure, heat of combustion, and spray droplet diameter. Using simultaneous OH Planar Laser Induced Fluorescence and Mie scattering imaging of the spray and flame structure, the liquid loading in the flame region is also analyzed for surrogate jet fuels which have comparable derived cetane number (DCN) but have very different compositions. Characteristics that can affect the amount of liquid fuel entering the flame region in near-LBO conditions are discussed. The use of surrogates allows for discussion of the competing effects of volatility and reactivity of fuel components. It is found that the most stable flames occur when the interplay of fuel atomization/volatility and reactivity result in substantial penetration of fuel droplets containing components with high DCN.