Browsing by Author "Costa, Mário"
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- Combustion behavior of Jet-A1 single droplets and its blends with Hydroprocessed Vegetable Oil in a drop tube furnacePublication . Pacheco, Gonçalo; Silva, A. R. R.; Costa, MárioThe aeronautical sector contributes significantly to greenhouse gases and pollutant emissions. The negative impact of these emissions in the environment has raised awareness for the introduction of alternative and greener fuels. The implementation of alternative fuels remains one of the main challenges for this sector in the near future. The aeronautical industry is characterized by the dependence on single fossil fuel and by a long service time of its assets. For these reasons, the main research drive has been around the development of “drop-in” fuels, which are alternative fuels that can be used in the already existing fleet without significant modifications. One of the proposed solutions is the blending of biofuels with jet fuel, which would allow the use of greener fuels and a reduction in greenhouse gases and emissions without significant changes in the existing companies’ fleets. In this context, the present work evaluates the ignition and the combustion of single droplets of jet-fuel, hydroprocessed vegetable oil (NExBTL), and their mixtures in a drop tube furnace. The main research focus of this study is to evaluate the influence of the mixture composition in the fuel-burning characteristics. Droplets with diameters of 155 ± 5 μm, produced by a commercial droplet generator, were injected into the top of the drop tube furnace. Three temperatures were investigated 900, 1000, and 1100 °C. The ignition and combustion of the droplets were evaluated through the images obtained with a high-speed camera (CR600x2) coupled with a high magnification lens (Navitar 6000 zoom lens) and treated with an edge detection algorithm. The images allowed for the observation of the burning phenomena, and the data reported the temporal evolution of the droplet sizes and burning rates. The pure fuels and mixtures followed the D2 law, except for the mixture with 75% jet-fuel/ 25% biofuel at 1100 °C that reveals disruptive burning phenomena contributing to the enhancement of the single droplet combustion. The disruptive burning phenomena are related to the appearance of “puffing” and micro-explosions at the end of the droplet lifetime.
- 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.
- Multiple impinging jet air-assisted atomizationPublication . Pizziol, Bruno; Costa, Mário; Panão, Miguel; Silva, A. R. R.The growth of the aviation sector triggered the search for alternative fuels and continued improvements in the combustion process. This study addresses the technological challenges associated with spray systems and the concern of mixing biofuels with fossil fuels to produce alternative and more ecological fuels for aviation. This work proposes a new injector design based on sprays produced from the simultaneous impact of multiple jets, using an additional jet of air to assist the atomization process. The results evidence the ability to control the average droplet size through the air mass flow rate. Depending on the air mass flow rate there is a transition between atomization by a hydrodynamic breakup of the liquid sheet formed on the impact point, to an aerodynamic breakup mechanism, as found in the atomization of inclined jets under cross-flow conditions. The aerodynamic shear breakup deteriorates the atomization performance, but within the same order of magnitude of the atomization efficiency. Finally, despite using different configurations (2, 3 and 4-impinging jets), the outcome is similar is terms of the sizes of drops produced, although increasing the number of impinging jets also implies some deterioration of the atomization efficiency.
- Multiple Impinging Jet Air-Assisted AtomizationPublication . Costa, Mário; Pizziol, Bruno; Panão, Miguel; Silva, A. R. R.The growth of the aviation sector triggered the search for alternative fuels and continued improvements in the combustion process. This work addresses the technological challenges associated with spray systems and the concern of mixing biofuels with fossil fuels to produce alternative and more ecological fuels for aviation. This work proposes a new injector design based on sprays produced from the simultaneous impact of multiple jets, using an additional jet of air to assist the atomization process. The results evidence the ability to control the average drop size through the air-mass flow rate. Depending on the air-mass flow rate there is a transition between atomization by hydrodynamic breakup of the liquid sheet formed on the impact point, to an aerodynamic breakup mechanism, as found in the atomization of inclined jets under cross-flow conditions. The aerodynamic shear breakup deteriorates the atomization performance, but within the same order of magnitude. Finally, our experiments show that mixing a biofuel with a fossil fuel does not significantly alter the spray characteristics, regarded as a step further in developing alternative and more ecological fuels for aero-engines.
- 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.
- Single droplet ignition and combustion of Jet-A1, vegetable oil and their blends in a drop tube furnacePublication . Pacheco, Gonçalo; Silva, A. R. R.; Costa, MárioThe aeronautical sector needs to introduce alternative fuels in order to achieve a reduction in greenhouse gas emissions. A possible solution in the near future might be the blending of biofuels with jet fuel, which would allow the use of a greener fuel without significant changes in the existing fleets of the companies, which means the development of a “drop in” fuel. The present work aims to study the ignition and combustion characteristics of single droplets of jet-A1 (JF), hydroprocessed vegetable oil (NExBTL) and their mixtures in a drop tube furnace (DTF). The droplets were injected into the DTF using a droplet generator. Experiments were conducted in air for three DTF wall temperatures (900, 1000 and 1100 ºC). The ignition and combustion of the droplets were evaluated through the images obtained with a high-speed camera coupled with a high magnification lens. The images allowed for the observation of the burning phenomena, and data are reported for temporal evolution of droplet sizes and burning rates. The results revealed that the mixtures followed the 𝐷2 law, except the mixture with 75% JF for a DTF wall temperature of 1100 ºC. This was due to the occurrence of puffing, which enhanced the burning rates. In addition, it was observed that the mixtures with higher content of JF present brighter flames, and higher burning rates.
- Single-Droplet Combustion of Jet A-1, Hydroprocessed Vegetable Oil, and Their Blends in a Drop-Tube FurnacePublication . Pacheco, Gonçalo; Silva, André; Costa, MárioThe environmental impact and the dependence upon fossil fuels in the aeronautical sector have promoted the demand for alternative and greener fuels. The implementation of alternative fuels is one of the main challenges for this sector in the near future. A possible short-term solution might be the blending of biofuels with jet fuel, which would allow for the use of greener fuels and a reduction in the greenhouse gases and pollutant emissions without significant changes in the existing fleets of the companies, with the purpose to develop a “drop-in” fuel. In this context, this work examines the combustion characteristics of single droplets of Jet A-1 (JF), hydroprocessed vegetable oil (NExBTL), and their mixtures in a drop-tube furnace (DTF). The objective of this work is to evaluate the influence of the mixture composition on the fuel characteristics. Droplets with diameters of 155 ± 5 μm, produced by a commercial droplet generator, were injected into the DTF, whose wall temperature and oxygen concentration were controlled. Experiments were conducted for three temperatures (900, 1000, and 1100 °C). The combustion of droplets was evaluated through the images obtained with a high-speed camera coupled with a high magnification lens and an edge detection algorithm. From the images allowed for the analysis of droplet combustion, data are reported for the temporal evolution of droplet sizes and burning rates. The results revealed that the mixtures followed the D2 law, except the mixture with 75% JF for a DTF wall temperature of 1100 °C. The 75% JF mixture did not follow the D2 law as a result of the occurrence of puffing and microexplosions, which enhanced the burning rates. Additionally, it was observed that the mixtures with a higher content of JF present brighter flames and higher burning rates.
- Sustainable aviation fuels and imminent technologies - CO2 emissions evolution towards 2050Publication . Abrantes, Ivo; Ferreira, Aana F.; Silva, André; Costa, MárioNowadays, concerns about rising emissions and climate change have raised the issue of decarbonization. Several approaches have been promoted in the aeronautical sector to reduce CO2 emissions. The present work provides quantitative data to support decision-making for the first pillar of International Air Transport Association (IATA) strategy to mitigate aviation climate impact. This strategy comprises improving aircraft technology and deploying sustainable low-carbon fuels. The most promising technologies for an imminent application are new engine architecture and natural laminar flow. On the other hand, efforts have been put to produce Sustainable Aviation Fuel (SAF) reaching the point where some methods for the production of alternative jet fuel are already approved by ASTM. Therefore, the present work quantifies the future reduction of CO2 emissions by 2050 in the aeronautical sector with these strategies. For this purpose, two methodologies are used, a numerical model to calculate fuel consumption and CO2 emissions from the global air transport fleet. For the SAF analysis, it is developed an approach that considers, besides the SAF production, the feedstocks, and the production pathway. Two cases and three scenarios represent the technological improvements and quantify the effects of new aircraft concepts and technologies on future CO2 emissions. For the SAF analysis, four scenarios and two conditions assess the different production capacities and feedstocks. The combined effect of technologies with SAF is considered verifying if the goals proposed by IATA, carbon-neutral growth from 2020, and a reduction of 50% in net emissions by 2050 compared to 2005 levels are achieved. The assessment results reveal that the goals cannot be met only with the combined action of imminent aircraft technologies and the use of alternative fuels. Carbon-neutral growth is only reached when it is considered the combined effect of technologies with the scenario where the amount of SAF introduced is higher (an increase of 15% annually between 2030 and 2050). However, this carbon-neutral growth is only possible to start in 2040. Imminent aircraft technologies can reduce up to 15% in CO2 emissions when compared to the Business as Usual scenario. The different feedstocks used in each process to produce SAF do not have a considerable impact on reducing CO2 emissions, the maximum difference registered between each condition was 1.47%.
- The impact of revolutionary aircraft designs on global aviation emissionsPublication . Abrantes, Ivo; Ferreira, Ana F.; Magalhães, Leandro; Costa, Mário; Silva, AndréThe discussion about the environmental impact caused by aviation has gained greater prominence due to the increased demand for this sector and, consequently, the increase in the number of flights. Environmental concerns have stimulated the development of novel approaches to reduce pollutants and CO2 emissions. This study aims to assess the impact of disruptive concepts on commercial aircraft by reducing CO2 emissions by 50% by 2050. In this regard the fleet system dynamics model is used to assess the effects of technological progress on future air transport systems. It accounts for the manufacturer’s production capabilities and current projections and forecasts on the needs and evolution of global air transport, as well as their expected entry into service. The main factors reported were production capacity, year of entry of the technology/concept, and the transport capacity and range of aircraft. The sensitivity study on the production capacity of new aircraft/concepts showed that with a 15% increase, emissions can be reduced between 1 and 2.6%, depending on the case and scenario. On the other hand, increasing the aircraft production capacity could lead to a problem of overcapacity.
- 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.