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- 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.
- 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.%.