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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.
- 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.
- 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.
- Single droplet combustion of aluminum nanoparticles added to a biofuel: effect of particle concentration and ambient temperaturePublication . Ferrão, Inês; Mendes, Miguel; Moita, A. S.; Silva, AndréThe fast expansion and growth of the aviation sector, coupled with the greenhouse gas andpollutant emissions, requires urgent solutions. A starting point to change this sector paradigmcould be a new energy source for aviation gas turbines, focused on potential carbon neutral fu-els, e.g., biofuels. A possible solution is nanoparticles addition to improve the biofuel propertiesand mitigate the problems inherent to their use. The present work experimentally evaluates thecombustion characteristics of single droplets of HVO (NExBTL) with aluminum nanoparticles.The ambient temperature was varied from600°Cto1000°C. Three particle concentrations (0.2,0.5, and 1.0 wt.%) were investigated with a fixed particle size of 40nm. This study examinedthe combustion of droplets with an initial diameter of 250μmusing a falling droplet method.The results reveal that for nanofuels, the droplet size evolution curve is not in agreement withD2– law and display a unique disruptive burning phenomenon at the end of the droplet life-time. It was noticed that the burning rate of biofuel is considerably enhanced with the addition ofnanoparticles, being the highest value for the nanofuel with a particle concentration of 1.0 wt.%.