Relationship Between Diesel Fuel Spray Vapor Penetration/Dispersion and Local Fuel Mixture Fraction

<div class="section abstract"><div class="htmlview paragraph">The fuel-ambient mixture in vaporized fuel jets produced by liquid sprays is fundamental to the performance and operation of engines. Unfortunately, experimental difficulties limit the direct measurement of local fuel-ambient mixture, inhibiting quantitative assessment of mixing. On the other hand, measurement of global quantities, such as the jet penetration rate, is relatively straightforward. Simplified models to predict local fuel-ambient mixture have also been developed, based on these global parameters. However, experimental data to validate these models over a range of conditions is needed. In the current work, we perform measurements of jet global quantities such as vapor-phase penetration, liquid-phase penetration, spreading angle, and nozzle flow coefficients over a range of conditions in a high-temperature, high-pressure vessel. Using this data and other quantitative mixing measurements performed by Rayleigh scattering in the vaporized portion of the jet, we compare to an existing variable-radial-profile model for prediction of fuel mixture fraction during the steady period of injection. Results show that spreading angles based on measurement of the most sensitive outer boundary of the jet, by schlieren or Rayleigh-scatter imaging, are needed as inputs to the model to obtain a match between modeled and measured fuel jet penetration rates. By adjusting the model (with spreading angle) to match the measured penetration, the model predictions also produce local mixture fractions that are within the Rayleigh scattering experimental uncertainty. Using this same penetration-matching technique, accurate model predictions of mixture fraction are achieved for a range of ambient densities, fuel injector nozzle shapes, injection pressures, and types of fuels. Additionally, extrapolation of the mixing measurements suggests that a fuel spray has a smaller spreading angle in the near-field and transitions to a larger angle in the far-field jet.</div></div>