A spatial technique providing global size and velocity data over a two-dimensional region of a sp... more A spatial technique providing global size and velocity data over a two-dimensional region of a spray is often preferred for rapid optical characterization of sprays. The Generalized Scattering Imaging (GSI) approach for droplet sizing, based on both the Lorenz-Mie theory and the Finely Stratified Sphere Scattering Model can be applied to both homogenous droplets and inhomogeneous and/or absorbing droplets. A new system has been developed using the GSI approach, with the capability to measure the velocity and size of droplets with non-uniform and/or varying refractive index, even in regions of high particle number density. A windowed FFT based approach was used to identify the presence and location of a droplet oscillation pattern, and an optimized frequency-based algorithm was used to extract the droplet size. A two-frame tracking algorithm was devised to measure the velocity of droplets from the two consecutive image frames. The size range and droplet concentration limits were inve...
ABSTRACT The emulsification is well known for being considered as a solution for improving biodie... more ABSTRACT The emulsification is well known for being considered as a solution for improving biodiesel combustion. In this extent, the size of the dispersed droplets is crucial to favour micro-explosions and optimising the combustion. The present mini-channel operates liquid/liquid dispersion at higher flow rates than with usual implementations of minichannels and micro-channels. Due to this particular condition of functioning, the flow enhanced in the mini channel is classified as a high-speed emulsifying one. In this study, the dispersion of water into sunflower oil as a water-in-oil (w/o) emulsion is tested. In such an in-line process, high-shear implies higher velocities at smaller scales, making an optical visualisation difficult. But the light scattering technique enables to detect micro-scaled droplets, at the required high velocities. The proper design and exploitation of a focalised laser beam through a transparent, hydrophobic mini-channel is explained. A focalised laser beam is crossing the mini-channel, dealing with the scattering cross sections of the water droplets. The measurement of the collected beam is successfully matched to the geometrical properties of the emulsion (water fraction and size of inner droplets) through the classical light scattering theoretical basement. The calibration of the collected laser light technique obtained in the straight mini-channel is followed by measurements approaching the high shear rate zone of the cross-flowing mini-channel.
ABSTRACT Combustion of water in oil μ-emulsions is still considered as a useful technology for th... more ABSTRACT Combustion of water in oil μ-emulsions is still considered as a useful technology for the energy conversion of waste oil. One of the most relevant advantages is related to the phenomenon of micro explosion (μ-e) that produces the secondary atomization of the oil. Several experimental approaches have been proposed in the last years with the aim to characterize the μ-e effect under different conditions. In this paper, an experimental comparison between the two useful approaches is presented. The results obtained with the technique of the Suspended droplet will be related to data present in the literature, obtained through the Leidenfrost technique. Quantitative thermal results such as the μ-e temperature and the fall temperature after μ-e show the most important differences. The important role played by the separation process as coalescence and creaming in both approaches is also discussed.
A new experimental technique for the determination of the size, velocity and/or the optical prope... more A new experimental technique for the determination of the size, velocity and/or the optical properties of single droplets is proposed. It is based on the different behaviour of scattering cross sections upon the size for vertically and horizontally polarized incident light, as it is predicted by the Lorenz-Mie theory. Measurements of the scattering polarization ratio y =CHH/Cvv in the side
The paper deals with the development of a dynamic model of a commercial 100 kW Micro Gas Turbine ... more The paper deals with the development of a dynamic model of a commercial 100 kW Micro Gas Turbine (MGT) fuelled with mixtures of standard (i.e. natural gas or methane) and alternative fuels (i.e. hydrogen). The model consists of a first-order differential equation (ODE) describing the dominant dynamics of the MGT imposed by its own control system during production electrical power. The differential equation is coupled to a set of nonlinear maps derived numerically from a detailed 0D thermodynamic matching model of the MGT evaluated over a wide range of operating conditions (i.e. mechanical power, fraction of hydrogen and ambient temperature). The efficiency of the electrical machine with power inverter and power absorbed by auxiliary devices is also taken into account. The resulting model is experimentally validated for a sequence of power step responses of the MGT at different ambient conditions and with different fuel mixtures. The model is suited for simulation and control of hybrid energy grids (HEGs) which rely on advanced use of MGT and hydrogen as energy carrier. In this regard, the MGT model is used in the simulation of an HEG based on an appropriate mix of renewable (non-programmable) and non-renewable (programmable) energy sources with hydrogen storage and its reuse in the MGT. Here, the MGT is used as a programmable energy vector for compensating the deficits of renewable energies (such as solar and wind) with respect to user demand, while excess renewable energy is used to produce hydrogen via electrolysis of water. The simulated HEG comprises a solar PhotoVoltaic (PV) plant (300 kW), an MGT (100 kW) fuelled with natural gas and hydrogen blends, a water electrolyzer (WE) system (8 bar, 56 Nm3/h), a hydrogen tank (54 m3), and an Energy Management Control System (EMCS).
ABSTRACT This article presents the results of experiments conducted aboard the International Spac... more ABSTRACT This article presents the results of experiments conducted aboard the International Space Station involving the combustion of large bi-component droplets of decane and hexanol (50/50 by volume) in air ambients with ambient pressures between 0.05 and 0.30 MPa. The experiments showed the presence of sustained low-temperature or cool-flame burning following radiative extinction of large droplets at ambient pressures greater than or equal to 0.10 MPa. The droplet diameters at cool-flame extinction were larger for the decane/hexanol droplets than for pure decane droplets at atmospheric pressure, suggesting that hexanol inhibits the cool-flame burning. At 0.20 MPa large fiber-supported droplets radiatively extinguished then burned with a cool flame for a period of time before the hot flame spontaneously re-ignited. At the highest ambient pressure of approximately 0.30 MPa the droplets again radiatively extinguished and burned with a cool flame. Contrary to the 0.20 MPa tests, however, the hot flame did not spontaneously re-ignite, but the droplet burned to completion with a cool flame. Further, more detailed analyses of all camera and radiometer data suggest that the cool-flame burning at 0.30 MPa is fundamentally different than the cool-flame burning at atmospheric pressure. This result does not appear to be consistent with expectations based on currently available cool-flame chemical kinetics and may suggest the need for a different chemical-kinetic mechanism.
A spatial technique providing global size and velocity data over a two-dimensional region of a sp... more A spatial technique providing global size and velocity data over a two-dimensional region of a spray is often preferred for rapid optical characterization of sprays. The Generalized Scattering Imaging (GSI) approach for droplet sizing, based on both the Lorenz-Mie theory and the Finely Stratified Sphere Scattering Model can be applied to both homogenous droplets and inhomogeneous and/or absorbing droplets. A new system has been developed using the GSI approach, with the capability to measure the velocity and size of droplets with non-uniform and/or varying refractive index, even in regions of high particle number density. A windowed FFT based approach was used to identify the presence and location of a droplet oscillation pattern, and an optimized frequency-based algorithm was used to extract the droplet size. A two-frame tracking algorithm was devised to measure the velocity of droplets from the two consecutive image frames. The size range and droplet concentration limits were inve...
ABSTRACT The emulsification is well known for being considered as a solution for improving biodie... more ABSTRACT The emulsification is well known for being considered as a solution for improving biodiesel combustion. In this extent, the size of the dispersed droplets is crucial to favour micro-explosions and optimising the combustion. The present mini-channel operates liquid/liquid dispersion at higher flow rates than with usual implementations of minichannels and micro-channels. Due to this particular condition of functioning, the flow enhanced in the mini channel is classified as a high-speed emulsifying one. In this study, the dispersion of water into sunflower oil as a water-in-oil (w/o) emulsion is tested. In such an in-line process, high-shear implies higher velocities at smaller scales, making an optical visualisation difficult. But the light scattering technique enables to detect micro-scaled droplets, at the required high velocities. The proper design and exploitation of a focalised laser beam through a transparent, hydrophobic mini-channel is explained. A focalised laser beam is crossing the mini-channel, dealing with the scattering cross sections of the water droplets. The measurement of the collected beam is successfully matched to the geometrical properties of the emulsion (water fraction and size of inner droplets) through the classical light scattering theoretical basement. The calibration of the collected laser light technique obtained in the straight mini-channel is followed by measurements approaching the high shear rate zone of the cross-flowing mini-channel.
ABSTRACT Combustion of water in oil μ-emulsions is still considered as a useful technology for th... more ABSTRACT Combustion of water in oil μ-emulsions is still considered as a useful technology for the energy conversion of waste oil. One of the most relevant advantages is related to the phenomenon of micro explosion (μ-e) that produces the secondary atomization of the oil. Several experimental approaches have been proposed in the last years with the aim to characterize the μ-e effect under different conditions. In this paper, an experimental comparison between the two useful approaches is presented. The results obtained with the technique of the Suspended droplet will be related to data present in the literature, obtained through the Leidenfrost technique. Quantitative thermal results such as the μ-e temperature and the fall temperature after μ-e show the most important differences. The important role played by the separation process as coalescence and creaming in both approaches is also discussed.
A new experimental technique for the determination of the size, velocity and/or the optical prope... more A new experimental technique for the determination of the size, velocity and/or the optical properties of single droplets is proposed. It is based on the different behaviour of scattering cross sections upon the size for vertically and horizontally polarized incident light, as it is predicted by the Lorenz-Mie theory. Measurements of the scattering polarization ratio y =CHH/Cvv in the side
The paper deals with the development of a dynamic model of a commercial 100 kW Micro Gas Turbine ... more The paper deals with the development of a dynamic model of a commercial 100 kW Micro Gas Turbine (MGT) fuelled with mixtures of standard (i.e. natural gas or methane) and alternative fuels (i.e. hydrogen). The model consists of a first-order differential equation (ODE) describing the dominant dynamics of the MGT imposed by its own control system during production electrical power. The differential equation is coupled to a set of nonlinear maps derived numerically from a detailed 0D thermodynamic matching model of the MGT evaluated over a wide range of operating conditions (i.e. mechanical power, fraction of hydrogen and ambient temperature). The efficiency of the electrical machine with power inverter and power absorbed by auxiliary devices is also taken into account. The resulting model is experimentally validated for a sequence of power step responses of the MGT at different ambient conditions and with different fuel mixtures. The model is suited for simulation and control of hybrid energy grids (HEGs) which rely on advanced use of MGT and hydrogen as energy carrier. In this regard, the MGT model is used in the simulation of an HEG based on an appropriate mix of renewable (non-programmable) and non-renewable (programmable) energy sources with hydrogen storage and its reuse in the MGT. Here, the MGT is used as a programmable energy vector for compensating the deficits of renewable energies (such as solar and wind) with respect to user demand, while excess renewable energy is used to produce hydrogen via electrolysis of water. The simulated HEG comprises a solar PhotoVoltaic (PV) plant (300 kW), an MGT (100 kW) fuelled with natural gas and hydrogen blends, a water electrolyzer (WE) system (8 bar, 56 Nm3/h), a hydrogen tank (54 m3), and an Energy Management Control System (EMCS).
ABSTRACT This article presents the results of experiments conducted aboard the International Spac... more ABSTRACT This article presents the results of experiments conducted aboard the International Space Station involving the combustion of large bi-component droplets of decane and hexanol (50/50 by volume) in air ambients with ambient pressures between 0.05 and 0.30 MPa. The experiments showed the presence of sustained low-temperature or cool-flame burning following radiative extinction of large droplets at ambient pressures greater than or equal to 0.10 MPa. The droplet diameters at cool-flame extinction were larger for the decane/hexanol droplets than for pure decane droplets at atmospheric pressure, suggesting that hexanol inhibits the cool-flame burning. At 0.20 MPa large fiber-supported droplets radiatively extinguished then burned with a cool flame for a period of time before the hot flame spontaneously re-ignited. At the highest ambient pressure of approximately 0.30 MPa the droplets again radiatively extinguished and burned with a cool flame. Contrary to the 0.20 MPa tests, however, the hot flame did not spontaneously re-ignite, but the droplet burned to completion with a cool flame. Further, more detailed analyses of all camera and radiometer data suggest that the cool-flame burning at 0.30 MPa is fundamentally different than the cool-flame burning at atmospheric pressure. This result does not appear to be consistent with expectations based on currently available cool-flame chemical kinetics and may suggest the need for a different chemical-kinetic mechanism.
Uploads
Papers by P. Massoli