Comparisons of Measured Drop Sizes and Velocities in a Transient Fuel Spray with Stability Criteria and Computed PDF's

Two sets of comparisons were made in an attempt to provide a mechanism for understanding the behavior of transient sprays. First, detailed measurements of drop size and velocity in a transient spray were compared to established stability criteria for different droplet breakup mechanisms, specifically criteria for bag breakup and boundary layer stripping. Then, probability-density-functions were determined from the experimental data and compared, where appropriate, to different computed distributions (such as the Chi-square or log-hyperbolic distributions).

Comparison with the stability criteria indicates that the a majority of droplets in the spray are susceptible to both breakup mechanisms near the injector tip. However, downstream, the spray appears to stabilize and any redistribution of droplet size must apparently be a result of collisions.

The experimentally-determined PDF's for size and velocity are functions of both position and time in the spray. Comparisons with computed PDF's show best agreement with the data for the multiparameter-dependent distributions, such as the chi-square or log-hyperbolic distributions.