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- Numerical Analysis of a Single Droplet Combustion of Jet-A1 and AlkanesPublication . Dias, Francisco; Ferrão, Inês; Mendes, Miguel; Moita, A. S.; Silva, A. R. R.The demand for aviation fuel is constantly increasing and has become apprehensive due to the depletion of fossil fuels. The use of petroleum sourced fuels as an energy source in the air transportation industry consists of an unsustainable alternative. Due to this, the introduction of alternative jet fuel is required to mitigate these issues. Thus, the present work simulates single droplet combustion numerically in a drop tube furnace. In this context, jet-A1 and n-Hexadecane were investigated. Additionally, it is studied the validation of approximating the combustion of alternative jet fuel to n-hexadecane. The employed model consists of a two-way coupling approach between the fuel droplets and the carrier fluid following an Eulerian-Lagragangian schematic. The continuous phase is primarily modeled and further coupled with the fuel droplets known as the discrete phase. A combustion model is employed in order to simulate the natural phenomenon of single droplet combustion to the intended utilized fuels. The results reveal that the droplet diameter reduces as the time evolves under the representation of the d2 law enabling the computation of different combustion characteristics being affected by the fuel composition.
- Experimental Investigation Of Disruptive Burning Phenomena On Nanofuel DropletsPublication . Ferrão, Inês; Mendes, Miguel; Moita, A. S.; Silva, A. R. R.The transport sector plays a crucial aspect in society and economic evolution. However, improper energy management has negatively impacted health and the environment. Thus, the use of sustainable and green fuels in the aeronautical industry has been implemented due to environmental concerns and the depletion of fossil fuels. The introduction of biofuels, a renewable energy source in the transportation sector, has shown advantages in terms of pollutant reduction. Recently, the addition of nanoparticles in the combustion of biofuel has been studied with the purpose of enhancing its combustion characteristics. Consequently, the present work evaluates nanofuel single droplet in a falling droplet method. In this way, the fiber suspension effect was neglected, and droplets in a size of 250 μm were evaluated. To this end, a comparison between pure biofuel and a nanofuel at two furnace temperatures (T = 800 ºC and T = 1000 ºC) was performed. The results reveal that disruptive burning phenomena occur when aluminum nanoparticles are added to the biofuel. Consequently, a micro-explosion determines the end of the droplet lifetime, mainly affected by the furnace temperature.
- A study of a single droplet impinging onto a sloped surface: Jet-Fuel and Biofuel mixturesPublication . Ferrão, Inês; Barata, Jorge M M; Silva, A. R. R.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, affecting 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.
- The Addition of Particles to an Alternative Jet FuelPublication . Ferrão, Inês; Mendes, Miguel; Moita, A. S.; Silva, AndréThe expansion of the research on nanoscale particles demonstrates several advantages in terms of stability and an increased surface area to volume ratio compared to micron-sized particles. Based on this, the present work explores the addition of aluminum particles in hydrotreated vegetable oil (HVO), an alternative jet fuel. To evaluate the influence of particle sizes, nano and micron particles (40 nm and 5 μm) in a particle concentration of 0.5 wt.% were stably suspended in HVO. This study evaluates droplet combustion with an initial diameter of 250 μm in a drop tube furnace under different furnace temperatures (600, 800, 1000 °C). A high magnification lens coupled with a high-speed camera provides qualitative and quantitative data regarding droplet size evolution and micro-explosions. Pure HVO and Jet A-1 were also tested for comparison purposes. The results reveal that the addition of aluminum particles enhances the alternative jet fuel combustion. Furthermore, decreasing the particle size and increasing the furnace temperature enhances the burning rate compared to the pure HVO. Pure HVO presents a burning rate nearly to 1.75 mm2/s until t/D20 = 0.35 s/mm2 at T = 1000 °C. When nanoparticles are added to HVO in a particle concentration of 0.5 wt.%, an improvement of 24% in burning rate is noticed. Conventional jet fuel and pure HVO do not present any disruptive burning phenomena. However, when aluminum particles were added to HVO, micro-explosions were detected at the end of droplet lifetime, regardless of the particle size.
- Combustion characteristics of a single droplet of hydroprocessed vegetable oil blended with aluminum nanoparticles in a drop tube furnacePublication . Ferrão, Inês; Silva, André; Moita, A. S.; Mendes, Miguel; Costa, MárioThis study examines the burning characteristics and disruptive burning phenomena of single droplets of aluminum nanoparticles (n-Al) stably suspended in a biofuel (HVO). The biofuel used in the present work is a promising alternative fuel already tested in the aviation sector to reduce greenhouse gas and pollutant emissions. Experiments were conducted with two particle sizes (40nm and 70nm) and two particle concentrations (0.5 wt.% and 1.0 wt.%) to study its influence when added to the biofuel. The effect of size and concentration of the aluminum nanoparticles was studied at 1100 °C in a drop tube furnace. This experimental facility allows the study of combustion characteristics of falling droplets, ensuring there is no influence of the supporting fiber on the burning rate and disruptive burning phenomena occurrence. A CMOS high - speed camera coupled with a high magnification lens was used to evaluate the droplet size, burning rate, and micro-explosions. Based on this procedure, pure biofuel droplets were compared with those of biofuel blended with nanoparticles. The results suggest that the combustion characteristics of pure HVO can be enhanced with the addition of aluminum nanoparticles. Furthermore, by decreasing the particle size, a slight increase in the burning rate of nanofuels was noticed. Additionally, an increase in the particle concentration leads to a pronounced increase in the burning rate. The particle concentration also influences the delay and intensity of micro-explosions, disruptive burning phenomena detected at the end of the droplet lifetime.
- Dynamic Behavior of a Single Droplet Impinging onto a Sloped SurfacePublication . Ferrão, Inês Alexandra dos Santos; Silva, André Resende Rodrigues daDroplet impact is a common phenomenon that occurs frequently in several applications such as fuel injection in internal combustion engines, processes involving spray paints and cooling of electronic equipment. Due to the technological advance, it becomes possible to observe in detail the dynamic impingement. In the study of droplet impingement, the influencing parameters are the liquid, along with its physical properties, the impact surface, the surrounding environment, or by the action of gravity. The combination of these terms lead to different and unique effects. The researches concerning the dynamic behavior of oblique impacts are scarce and not fully understood. Consequently, it was decided to deepen its theme through the development of this work. The major goal of the present work is a comparison that involves an experimental study of the phenomena occurring during the impact of liquid droplets onto a dry surface with a cross flowing air and droplets impact onto a sloped surface, using two dry aluminum plates with mean roughness (Ra= and Ra= ). Due to the crossflow, the droplet does not have the same direction as the gravitational acceleration and suffers a certain deformation that seems to vary the condition. For the sloped surface, the droplet is spherical throughout the trajectory and both the gravitational acceleration and movement of the droplet have the same direction. In this study, it was considered a crossflow velocity of 7m/s and it was designed a mechanism that has the possibility to vary the surface angles. Four fluids were used: 100% Jet-Fuel, 75%JF - 25%HVO, 50%JF - 50%HVO and H2O (pure water) as a reference. It was considered a combination of a conventional jet fuel and a biofuel (HVO – Hydroprocessed Vegetable Oil), more specifically Jet A-1 and NEXBTL, with the aim to implement new alternatives to reduce the pollution levels. It is through these innovations that it is possible to improve various systems such as piston engines or gas turbines with alternative fuels. In order to maintain the coherence of the results between the two experimental works, the impact velocity and incident angle were kept approximately the same, in the two activities. Due to the different impact conditions, only two phenomena were expected for this comparison: spreading and splash. A MATLAB algorithm was developed to achieve the different droplet diameters and impact velocities. The researches concerning the dynamic behavior of oblique impacts are scarce, and not fully understood. The experimental data obtained allows comparing the splashing thresholds available in the literature. The purpose of this empirical correlations is to predict the transition between deposition and splash. Therefore, the normal impact was also studied and analyzed the splash/non-splash transition for the two impact surfaces analyzed.
- The Impact of High Particles Concentration in a Biofuel Droplet CombustionPublication . Mendes, Tomás S. M.; Ferrão, Inês; Mendes, Miguel; Moita, A. S.; Silva, A. R. R.Aviation is one of the largest transportation sectors and is operated on fossil fuels, being responsible for about 2% of global CO2 emissions. In order to reduce the environmental impact, biofuels emerged as a promising solution. Additionally, a possible approach to improve the performance of biofuels is to add nanoparticles, leading to the concept of nanofuel. The present work evaluates the nanofuel droplet combustion of a biofuel containing high aluminum particle concentrations. To enhance the nanofuel stability, a preliminary study focusing on the addition of a surfactant was mandatory. Particle size of 40 nm and three particle concentrations from 1.0 to 4.0 wt.% were considered. The results show that the oleic acid effectively improves the stability, and no visible oxidation of the nanoparticles was reported. Regarding the single droplet combustion, the observations show that the addition of nanoparticles promotes micro-explosions, contrary to the combustion of pure biofuel, and increases the overall droplet burning rate.
- Single droplet combustion of aluminum nanoparticles added to a biofuelPublication . Ferrão, Inês; Silva, A. R. R.; Moita, A. S.; Mendes, Miguel; Costa, MárioThe present work evaluates the evaporation and combustion of single droplets of a biofuel (HVO) added with aluminum nanoparticles (n-Al). Tests were carried out in a drop tube furnace that allows the control of the wall temperature and oxygen concentration, in which the single droplets were injected downward at the top of the furnace. Droplets with a diameter of 250 μm were generated from a commercial droplet generator. Experiments were conducted with two particle sizes (40 nm and 70 nm) and two particle concentrations (0.5 wt.% and 1.0 wt.%). The effect of the size and concentration of the aluminum nanoparticles added to the biofuel was studied at 1100 °C. Detailed measurements, namely the temporal evolution of the droplet size and burning rate, were analyzed post-processing images. The combustion of aluminum nanoparticles added to a biofuel reveals micro-explosions, a disruptive burning phenomenon that appears at the end of the droplet lifetime, which is greatly influenced by the particle concentration.
- The influence of aluminium particles in a Hydroprocessed Vegetable Oil combustionPublication . Ferrão, Inês; Silva, A. R. R.; Moita, A. S.; Mendes, Miguel; Costa, MárioThe present work experimentally investigates single droplet combustion to understand the effect of aluminum particles when added to a biofuel. Experiments are carried out in a drop tube furnace to evaluate the influence of size and concentration of the aluminum particles. Two different sizes (40 nm and 5 μm) and two concentrations (0.5 and 1.0 wt.%) are studied at 1000 °C. The addition of aluminum particles improves biofuel combustion. Decreasing the particle size and increasing the particle concentration leads to a significant enhancement in the burning rate compared to the pure HVO. Micro-explosions are detected at the end of droplet lifetime when particles are added to biofuel.
- Influence of aluminum nanoparticles in alternative fuel: Single droplet combustion experiments and modelingPublication . Ferrão, Inês; Mendes, Tomás; Mendes, Miguel; Moita, A. S.; Silva, A. R. R.In this work, the effect of adding aluminum nanoparticles on hydrotreated vegetable oil was investigated experimentally and numerically in terms of nanofuel stability and single droplet combustion. The purpose is to understand the phenomena related to isolated droplet combustion when metallic particles are added to a liquid biofuel. Falling droplet combustion experiments were conducted in a drop tube furnace at two different furnace temperatures (800 C and 1000 C) using a high-speed camera coupled with a high magnification lens to investigate the droplet size evolution as disruptive burning phenomena. In numerical terms, a simplified macroscopic model was developed to predict the burning behavior of isolated nanofuel droplets, considering hexadecane as a surrogate fuel for the biofuel. The results reveal that adding nanoparticles resulted in a departure from the -law. Moreover, an increase in the overall droplet burning rate was observed, and according to the numerical results, nanoparticle radiation absorption is the responsible mechanism. Micro-explosions occurred for all nanofuels, and this disruptive burning behavior substantially influenced the droplet lifetime.