Browsing by Issue Date, starting with "2018-07-22"
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- Dynamic behaviour of single droplets impinging upon liquid films with variable thickness: Jet a-1 and hvo mixturesPublication . Ribeiro, Daniela; Cunha, Nuno; Barata, Jorge M M; Silva, AndréFortunately, the human being has already started to be environmentally concerned and the search for new alternatives to reduce pollution increased. Transports are responsible for a significant portion and it is extremely necessary to bet on alternatives to oil. The introduction of biofuels in aero-engines could be an example. In order to modify and optimize piston engines and gas turbines to operate efficiently with alternative fuels, this work used Jet Fuel and Biofuel mixtures. The focus of these studies was to visualize the dynamic behavior of single droplets impinging upon liquid films with variable thickness. The existence of splash as well as its characteristics were reported and the differences and similarities between the outcomes according to the impact conditions and the fluid properties were catalogued. To achieve that an experimental facility was designed and built. Four fluids were tested: water (as reference), 100% Jet A-1, 75%/25% and 50%/50% mixtures of Jet A-1 and HVO (Hydro-processed Vegetable Oil), respectively, since civil aviation only accept mixtures with at least 50% Jet Fuel in volume. The fluid properties were measured to ensure accuracy. The liquid film depths considered were 10%, 50% and 100% of the droplet diameter. A high-speed digital camera was used to image acquisition and the droplet was released by a syringe pump connected to the needle at a specific pumping rate. The impact surface was a perspex container filled with fluid. Five needles with different inner diameters and three impact heights were employed to provide a variety of Weber and Reynolds numbers.
- The splash deposition transition limits of a biofuel droplet wall impact with a and without crossflowPublication . Cunha, Nuno; Ribeiro, Daniela; Barata, Jorge M M; Silva, AndréOver the last years, there have been many investigations into new ways to obtain clean and efficient energy production. In this spirit, this study aims to successfully adapt low emission aero-engines combustors to burn biofuels. Biofuels are the immediate alternative to fossil-fuel powered aero-engines, given that by regulation is possible to apply today, a biofuel into the aeronautical industry. There are some regulations to have into account, being the biggest one the fact that the new blend must be constituted of at least 50% of conventional jet fuel (JF). In this work were selected four blends to study: 100% JF; 75% JF and 25% NEXBTL (biofuel); 50% JF and 50% NEXBTL and H2O. A smooth, dry aluminium plate was used as the impact surface and the objective was to observe the splash-deposition limits and characterize the dynamic behaviour of the droplets with and without crossflow. Different velocities of the crossflow were chosen and the impact angle of the droplet was also analysed. The splash-deposition threshold was also compared with those proposed by other authors.