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- Experimental Study of a Single Droplet Impinging on Dry Surface with and without a Crossflow: Jet Fuel and Biofuel MixturesPublication . Cunha, Nuno Filipe Costa; Silva, André Resende Rodrigues daThe impact of droplets on different surfaces is a very complex and important phenomenon and it has variety of applications such as fire suppression systems, spray painting, crop spraying and blending preparation in internal combustion engines. Although these phenomena are widely studied, the present work aims to study the influence in mixing a biofuel in a conventional jet fuel and characterize the impact result of the droplets in these mixtures. This study allows the development of numerical models to determine the limit of the different impact phenomena. ln this study, an experimental facility was designed to study the droplet impact behavior on a smooth, dry aluminum surface. Four substances were analyzed: two mixtures (75% JF - 25%HVO and 50% JF - 50% HVO) and two other substances (100% JF and H20). Jet fuel was used to compare the effect of biofuel on the impact result, and H20 was used as the control substance. It was observed that the blends exhibit a different splash / non splash threshold suggesting that the biofuel properties influence the impact result_ To study the effect of a crossflow in this phenomenon , a wind tunnel was also designed and a comparison between normal impact and impact with a crossflow was made. Three crossflow velocities were used and the velocity of the impact was divided into two velocity vectors. Different results were observed comparing crossflow impact with normal impact and the velocity components seem to have some significance in the transition of the impact phenomena. The results were compared with some transition criteria proposed in the literature and the data indicate that none of them presents a good correlation for the data. It was also verified that a study of the surface roughness of the used plate would allow drawing more conclusions.
- 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.