Formation and diagnostics of sprays in combustion

Fuel-air mixture preparation is a key factor determining combustion performance and emissions in a variety of practical applications, such as internal combustion engines, gas-turbine engines, rocket propulsion devices, and power generation systems. The problem of characterizing the two-phase combustion process, however, is quite difficult in part because of the complex optical interactions involved, as well as the optically dense nature of many sprays. There are a wide number of techniques currently employed for the characterization of spray combustion processes, with the selection of appropriate measurement technology dependent upon the nature of the spray for each combustion application. This chapter reviews a variety of conventional techniques, in particular Mie scattering, phase-Doppler interferometry, and planar laser-induced fluorescence. More advanced techniques, including holography, three-dimensional tomography, X-ray radiography, and time-gated ballistic imaging are also discussed. Often the combination or comparison of multiple techniques yields information that would otherwise be inaccessible with individual methods. Advantages and disadvantages of each technique, sources of error, measurement needs, and outlook for future development are discussed in the context of the challenges facing combustion scientists and engineers