# Experimental Characterization of Two-Phase Aerated Liquid Ethanol and Jet A Spray Flames +
## 2 Experimental Setup
The lower Jet A liquid flow rate than that of ethanol was chosen after preliminary observation indicated better similarity in flow behavior to ethanol at the various levels of oxygen input; therefore, the 2 mL/min liquid flow rate was anticipated to produce observable differences in atomization for the same range of oxygen levels. At an oxygen flow rate setting of 0.10 L/min, the liquid stream was already exhibiting break-up, though the liquid structures were still relatively large until the oxygen flow rate had been increased to 0.25 L/min. Droplet size and distribution qualitatively appeared to be the most uniform when oxygen was flowing at 0.40 L/min. Figure 2: Shadowgraph images of ethanol spray at 4 mL/min fuel flow rate and variable oxygen flow rates. Calculated oxygen dynamic pressures and equivalence ratios are given. Though shadowgraphy does not provide quantitative droplet size information as noted at the beginning of this section, a simplified image contrast analysis was performed to obtain a general predicted droplet probability distribution by diameter for the shadowgraphs, shown in Figure 4. The analysis was performed on 100-shot shadowgraph image sets in each case using particle detection commands in MATLAB, in which the images were reduced to binary black-and-white with 50% thresholding and particles greater than 500 \(\upmu\)m were ignored. The MATLAB command for determining properties of image regions (regionprops) was used to detect particles in the 50% thresholded black-and-white images, and the particle data were then passed into the probability distribution function (pdf) command. The centroids and major axis lengths of standout objects (i.e., diameter of droplets and liquid ligaments which were of high contrast to the background and therefore preserved by the image thresholding) were automatically detected by the regionprops command and were used to estimate the number of particles for a given droplet diameter, and the detected particle data was then used to generate the probability distribution functions of particle size. The image thresholding caused the central region of the spray to appear as an amalgamated singular structure, but the well-resolved and relatively sparse droplets at the edge of the spray could be identified by the particle detection algorithm. Due to the magnification and the resolution of the camera's \(512\times 512\) pixel array, droplet  
Figure 3: Shadowgraph images of Jet A spray at 2 mL/min fuel flow rate and variable oxygen flow rates. Calculated oxygen dynamic pressures and equivalence ratios are given. diameters below \(\sim\)30 \(\upmu\)m were not resolved, therefore the probability distributions should be interpreted as models of the droplet atomization rather than precision measures of it. The probability distributions predicted that the peak droplet distribution occurred near \(\sim\)50 \(\upmu\)m with the highest probabilities when the O\({}_{2}\) flow rate was 0.35 to 0.50 L/min. Although the probability distribution for the O\({}_{2}\) flow rate of 0.10 L/min was anomalous and is excluded from the plot since its shadowgraphs displayed a nearly uniform stream with no discernable droplet breakup for each of the 100 shots, the remaining probability distributions show a trend of increasingly smaller droplets in larger concentrations as the O\({}_{2}\) flow rate was increased. Similar to the ethanol spray, the Jet A spray droplet probability distribution exhibited increasing concentrations of decreasing droplet diameters as the O\({}_{2}\) flow rate was increased. Further experiments were performed to characterize spray flames from the nebulizer. Equivalence ratios of 6.56, 7.55, 8.06, and 10.9 were used with constant oxygen flow rates in order to provide a range of fuel presence.