Group combustion models and laser diagnostic methods in sprays: A review

Fundamental combustion processes in liquid fuel sprays are reviewed. Group combustion theories for calculation and prediction of spray flame characteristics are examined. Numerical analyses for sprays with varying group combustion numbers and fuel air ratios are reported showing locations of flame fronts, critical group combustion numbers, and group burning rates. The validity of the assumptions and the predictions of flame characteristics require testing by measurement. The most recent developments in laser diagnostic techniques for measurement of drop size by TV imaging, holography, visibility, peak pedestal amplitude, and intensity ratioing using laser Doppler interferometry are discussed together with Fraunhofer diffraction for overall particle cloud analysis. Instruments are commercially available for simultaneous measurement of drop size and velocity of individual drops in spray flames. Directives for future research on spray combustion processes are given with recommendations for making measurements in continuous and intermittent high-density vaporizing spray flames for the determination of local and overall transport processes.