Design and experimental characterization of an air-assisted, impinging-jets atomizer for aeronautical applications with biofuel

The increasing concerns over the emissions of greenhouse gases, coupled with the continuous growth of civil aviation, raised the interest over the development of new solutions to reduce the environmental impact of the sector. In the present contribution, an innovative technique for the atomization of aviation fuel has been investigated. The technique consists of the combined use of two separated and established technologies: the pneumatic atomization, which is already widely used in aeronautical turbines, and the impinging-jets atomization, which use is nowadays limited to rocket engines. Moreover, the investigations have been operated with an alternative biofuel of the HEFA class, in order to assess its performances and evaluate its fitness for the aeronautical applications. The characterization of the atomizing spray has been operated through a non-invasive optical technique based on the diffraction of monochromatic light, which allowed the measure of the sample Sauter Mean Diameter. Furthermore, a high-speed camera has been employed to capture the impingement region, in order to relate the measured SMD values with the morphology of the breakup phenomenon. The experimental activities have been operated over a wide range of conditions: with two different fuels (the alternative HEFA-based fuel and the conventional counterpart), both different air and fuel mass flows, different atomizer geometrical configurations and different conditions of nozzle alignment. The results showed a general good atomization for the combined technique, which allows to reach thin droplet sizes on low required values of Air-to-Fuel Ratio. The alternative fuel, compared to the conventional jet fuel, showed a worse performance (as consequence of the different properties), but achieved, even though inferior, similar values of SMD, and therefore holds as an option of great interest for the use as drop-in fuel in aeronautical turbines.