# Experimental Characterization of Two-Phase Aerated Liquid Ethanol and Jet A Spray Flames +
## 2 Experimental Setup
The oxygen flow rate was set at 0.4 L/min for both fuels based on qualitative observation as well as the indications of sufficient droplet breakup from the probability distributions shown in Figure 4, and the target equivalence ratios corresponded to liquid flow rates (in mL/min) of 2.28, 2.63, 2.80, and 3.80 for ethanol and for Jet A 1.32, 1.52, 1.62, and 2.19. These flow settings were arrived at from initial experimentation to determine optimum ignition stability for the setup. Shadowgraphs of cold- and ignited-flow ethanol sprays for four equivalence ratios are shown in Figure 5. The images are 100-shot averages, with the ignited flow average image subtracted from the cold-flow image to obtain the estimated lifted flame height from the dark regions in the difference image. The flame appeared to begin \(\sim\)6 mm above the nozzle exit in each case based on the difference images. The flame maintained a cylindrical shape, however the flame lift height above the nozzle was visually observed to be uneven, and this discrepancy was attributed to annular asymmetry of the gas co-flow due to a minor manufacturing error. Shadowgraphs of Jet A sprays under the same  
Figure 4: Droplet probability vs. droplet diameter for ethanol and Jet A spray shadowgraphs from Figures 1 and 2. The probability distribution functions were calculated for 100 images at each flow rate for detected droplets up to 500 \(\upmu\)m in diameter. conditions are shown in Figure 6. The flame height again appeared to begin \(\sim\)6 mm above the nozzle exit. The similarity of the lifted flame height for both fuels across different equivalence ratios suggests that the nebulizer promotes flame stability; droplet evaporation may deliver reliable establishment of a prime mixture fraction for sustained combustion. Figure 5: Shadowgraph images of ethanol spray at four equivalence ratios. Shadowgraphs are averaged from 100 sequential shots. The O\({}_{2}\) flow rate was fixed at 0.4 L/min. Mie scattering was used to detect liquid concentration in cold- and ignited-flow ethanol sprays under the four equivalence ratios, as shown in Figure 7. A total of 100 sequential shots at an exposure time of 1 ms each were taken of both non-ignited and ignited flow. The shot groups were averaged to produce the images shown in the figure. Flame emission at 632.8 nm was removed by subtracting the images. The images were averaged to produce the images shown in the figure. Flame emission at 632.8 nm was removed by subtracting the images. Flame emission at 632.8 nm was removed by subtracting the images. 100-shot averaged images of the ignited flow without the laser sheet present from the Mie scattered ignited flow images; this was done to prevent any flame chemiluminescence detectable after passing through the line filter from interfering with the Mie scattering signal. The images are normalized to the maximum value of each image; the normalization scale corresponds to scattering intensity, i.e., local liquid concentration. The difference images, obtained by subtracting the ignited flow image from the cold flow image as in Figures 5 and 6, show that the flame height occurred near 6 mm above the nozzle in all cases, corroborating the shadowgraph data. Mie scattering data for the Jet A sprays with the four equivalence ratios is shown in Figure 8. Again, the flame height was observed to begin \(\sim\)6 mm above the nozzle similarly to the shadowgraph data. Spray angles for both fuels in non-ignited and ignited conditions are summarized in Table 1 and shown in Figure 2:0 The angles were determined from the flow at the nozzle exit in the Mie scattering images using the angle measuring tool in ImageJ. Spray angles showed an increasing trend correlating to increasing liquid concentration, suggesting heavier liquid flow was associated with a greater degree of spread from the nozzle exit.