A study of a single droplet impinging onto a sloped surface: Jet-Fuel and Biofuel mixtures
Inês Ferrão  1, 2@  , Jorge Barata  1, 2@  , André Silva  1, 2, *@  
1 : University of Beira Interior [Portugal]
UBI, Covilhã, PortugalRua Marquês D'Ávila e Bolama. 6201-001 Covilhã. -  Portugal
2 : LAETA\UBI_AEROG-Aeronautics and Astronautics Research Center
Edifício II das Engenharias, 6201-001 Covilhã -  Portugal
* : Corresponding author

The present study experimentally investigated droplets impinging on a sloped aluminum surface. In these experiments, the droplet is spherical throughout the trajectory where the gravitational acceleration and movement of the droplet have the same direction, which leads to unique phenomena. Considering an oblique impact, the droplet collides with a certain angle, and the impact velocity is composed of normal and tangential components to the surface that vary with the impact height. Four fluids were tested: 100% Jet-Fuel, 75% Jet-Fuel/ 25% HVO, 50% Jet-Fuel/ 50% HVO and H2O (pure water) as a reference. The mixtures were a combination of a conventional Jet Fuel (Jet A-1) and a biofuel (HVO – Hydroprocessed Vegetable Oil), more specifically NEXBTL. When a droplet impacts onto an inclined surface, its shape is distorted and it can spread or splash asymmetrically relatively to the point of impact, which also affects the advancing and receding contact angle. Therefore, several geometric parameters were measured and compared for the different fluids and incident angles. The incident angles influence the spreading velocity on the upper and lower side. The spreading velocity was analyzed, allowing a better understanding of the dynamic behavior of each side. The spread factor, which corresponds to the distance between the lower and upper edges normalized by the initial droplet diameter, was compared to the Weber number (We) which is a proper indicator for the drop deformation. The variation of incident angles and impact velocity promotes a different droplet movement and asymmetry in phenomena that are also evidently influenced by the gravity role.

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