# Experimental Characterization of Two-Phase Aerated Liquid Ethanol and Jet A Spray Flames +
## 1 Introduction  
Two-phase combustion flows play extremely important roles in the aircraft propulsion [1; 2], power [3], petroleum [4; 5], and chemical [6; 7] industries. In particular, aerated liquid sprays have been shown to effectively shatter the fuel jet or sheet into ligaments and then droplets for propulsion applications [8; 9]. Additionally, it has been shown that the liquid aeration technique can generate a spray that penetrates deeply into high-speed crossflows and produces favorable plume/droplet properties, such as a high-concentration of smaller droplets distributed over a larger plume cross section [10; 11]. Aerated nozzles such as those studied in [8; 9; 10; 11] typically introduce air into the liquid stream through interior injectors upstream of the nozzle exit. Another type of aerating spray nozzle is the air-assisted atomizer; in this design, the liquid injector is surrounded by an annular air chamber, with the liquid injector terminating before the nozzle exit where the liquid stream is joined by the expelled high-speed air flowing from the chamber to promote liquid structure break-up. Nebulizers are a third type of aerating spray nozzle. The nebulizer design principle is similar to the air-assisted atomizer type, except that the co-flowing air combines with the liquid stream right at the exit as both fluids are expelled, rather than internally prior to exiting the nozzle. The resulting liquid spray is well-distributed and reliably consistent. Air-assisted atomizers and nebulizers have been utilized in the study of mixed spray flames [12; 13; 14; 15]. While initial studies of applicable spray nozzle designs for fuel injection may be conducted with a commonly available test liquid (e.g., water), qualitative and quantitative characterizations are needed for practical fuels. Aviation fuels such as Jet A must be characterized individually, since the fuel properties of surface tensions and evaporation rates are dramatically different from water, ethanol, and transportation fuels [16]. The use of actual fuel injectors or custom atomizing nozzles for spray combustion analysis under practical conditions may not be feasible without appropriate test rigs. Laboratory-grade two-phase flow systems with well-defined characteristics of air/liquid flow rates and dimensions can provide benchmark data of two-phase flows and flames. In this work, a commercially available nebulizer from Meinhard designed for benchtop chemical experimentation is utilized for combusting spray diagnostic applications. The Meinhard nebulizer is similar to the model used in [15] but is of different geometry. This work presents an initial characterization of the Meinhard nozzle's spray under variable fuel-air mixture conditions controlled by alteration of the fluid flow rates. Ethanol and Jet A in cold-flowing and combusting conditions are the demonstration fuels. Three optical diagnostic tools (shadowgraph, Mie scattering, and high-speed chemiluminescence imaging) are used to characterize the developed region of two-phase liquid ethanol and Jet A spray flames at atmospheric pressures. Shadowgraphy is a well-known line-of-sight diagnostic [17] that has been used to measure liquid spray penetration depth, angle, spray area, and spray development upon wall impingement [18; 19; 20; 10]. Mie scattering from the interaction of laser light with liquid sprays has been utilized for quantitative measurements of the concentration of liquid droplets and soot particles in sprays. The droplets scatter light much more intensely than the gaseous material [22; 23; 24]. This intense scattering is governed by Mie theory and measurement of the intensity yields quantified concentration and distribution data. Flame chemiluminescence provides information about flame structure and is applicable to ignited fuel sprays.