# Experimental Characterization of Two-Phase Aerated Liquid Ethanol and Jet A Spray Flames +
## 2 Experimental Setup  
The experiments were performed on a borosilicate glass aerated nebulizer designed by [PERSON] (part number TR-50-A0.5). The nebulizer had a liquid input capillary surrounded by an annular concentric tube for gas dispersion, converging to a 2 mm diameter nozzle with 0.4 mm capillary inner diameter, 14 \(\upmu\)m annular separation at the nozzle, and 0.022 mm\({}^{2}\) annular area. Liquid fuel was released from the nozzle's input capillary with oxygen co-flowing through the annular tube, resulting in a finely atomized spray of micro-scale droplets. An image of the nozzle is shown in Figure 1a. Ethanol was used for the initial nozzle characterization, and Jet A was used for a practical comparison. Liquid flow rates were controlled by an electronic syringe pump and oxidizer air flow rates were controlled by a flow controller; flow settings were established for equivalence ratios (denoted by \(\varphi\)) of 6.56, 7.55, 8.06, and 10.9 by leaving the air flow constant and changing the liquid flow rate. During the initial characterization of the nozzle, the ethanol flow rate was 4 mL/min and the oxygen flow rate was 0.4 L/min with input pressure of \(p_{r}=345\) kPa and exit pressure of \(p_{e}=114\) kPa. The nozzle's hydraulic diameter was \(D_{h}=28\)\(\upmu\)m and its Reynolds number was \(ReD_{h}=6400\). When the spray was ignited, continued droplet vaporization and mixing with the room air caused self-sustaining combustion conditions to occur. The spray output was directed toward an outlet duct with a light suction force, which both exhausted the spray out of the room through a fume hood and helped to sustain its directional uniformity. The velocity of the air into the duct was not measured but the suction force was observed to be of a minimal degree, provided by the fume hood's drawing of the room air through the duct. A time-gated, intensified CCD camera (Princeton Instruments PI-MAX4) with a 50 mm lens was used for shadowgraph imaging. The camera's pixel array was \(512\times 512\). Shadowgraph experiments were performed with the spray nozzle tip placed in front of collimated white light and the shadows of the spray droplets projected directly into the camera lens. Images were collected sequentially with a gate width of 10 \(\upmu\)s. A diagram of the shadowgraph setup is shown in Figure 1b. A Nikon DSLR camera with a 50 mm lens was used for imaging of Mie scattering and flame chemiluminescence of CH\({}^{\star}\), CO\({}_{2}\)\({}^{\star}\), and C\({}_{2}\)\({}^{\star}\). The light source for Mie scattering was a continuous He-Ne laser with a wavelength of 632.8 nm; the camera was fitted with a 632.8 nm line filter to eliminate background light. The laser beam was passed through the appropriate optics to be formed into a sheet which illuminated the spray, and the Mie scattering from the droplets was detected by the camera placed perpendicularly to the laser sheet. A diagram of the Mie scattering setup is shown in Figure 1c. Chemiluminescence emissions of ignited sprays were detected by pointing the camera at the spray and imaging through a filter. The filters used were of 430, 450, and 513 nm wavelengths, appropriate for detecting the chemiluminescence emissions for CH\({}^{\star}\), CO\({}_{2}\)\({}^{\star}\), and C\({}_{2}\)\({}^{\star}\), respectively, and simultaneously removing other emissions. Figure 1: \(Cont\). outlet is anticipated when the O\({}_{2}\) flow rate is raised above \(\sim\)0.45-0.50 L/min, therefore further increase in the gas flow rate would not cause the dynamic pressure to rise any higher without changing the experimental conditions (i.e., using a different gas for air injection). Experimentation with higher gas flow rates than 0.50 L/min correlated to this assumption, as it did not demonstrate any notable effect on the spray dynamics. Single-shot shadowgraphs for Jet A sprays held at 2 mL/min liquid flow rate and with varied gas flow rates are shown in Figure 3, with calculated equivalence ratios and gas dynamic pressures.