ILASS Americas, 23 rd Annual Conference on Liquid Atomization and Spray Systems, Ventura, CA, May 2011 ___________________________ * Corresponding author Measurement Uncertainty of Liquid Penetration in Evaporating Diesel Sprays Lyle M. Pickett* Sandia National Laboratories Livermore, CA 94551 USA Caroline L. Genzale Department of Mechanical Engineering Georgia Institute of Technology Atlanta, GA 30030 USA Julien Manin CMT-Motores Térmicos Universidad Politécnica de Valencia Valencia, Spain Louis-Marie Malbec and Laurent Hermant IFP Energies Nouvelles Rueil-Malmaison, France Abstract Quantitatively robust spray penetration measurements are of key importance for model development and validation. However, the most widely used light-scatter measurement techniques are not fully quantitative. Without a strict quantification of the liquid distribution, the measurement technique selected and/or the details of the experimental setup may significantly influence the reported liquid penetration. Furthermore, the detected liquid-phase penetration length in an experiment may not be consistent with the definition used in a model, making a comparison between the two indirect. Thus, there remains a need to assess the physical meaning of experimentally measured liquid lengths in order to provide a direct relationship with model-based predictions. In the current work, we compare nine different light-scatter and extinction diagnostics for measurement of the liquid length of an evaporating diesel spray in a high-pressure, high-temperature optical vessel. Results show that light- scatter imaging is sensitive to the orientation of the illumination source, producing different maximum intensity locations depending upon the optical setup. However, the scatter intensity from many different setups can be norma- lized by reference to that at a particular axial distance. Light-extinction diagnostics are more quantitative because of a built-in reference light intensity, but can be sensitive to beam-steering effects due to refractive index gradients. The most quantitative diagnostic for light extinction in this study is a small laser with divergence accommodation using an integrating sphere. Using an axial position for liquid length defined based on 3% of the maximum scatter intensity and the measured optical thickness at the same location, we apply Mie-scatter theory to estimate the liquid volume fraction pertaining to this defined liquid length for the particular experimental conditions of this study. Assuming droplet diameters at this liquid length have size ranges from 0.1 µm to 10 µm yields an upper-bound estimate for the path-length-averaged liquid volume fraction of 0.15%. Analysis of the experimentally measured light-scatter and extinction signals provides an improved assessment of the physical meaning of liquid-length mea- surements in diesel sprays, and provides better guidance for comparison to CFD modeling.