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Efficient blue-white color luminescence with near-ultraviolet excitation in Dy3+/Tm3+:Na3Gd(PO4)2 nanophosphor for white LEDs
摘要： The Dy3t/Tm3t ions co-activated Na3Gd(PO4)2 phosphors were synthesized by the citrate-gel based combustion technique. The structural properties of as-synthesized phosphors were studied through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The influence of Tm3t concentration on the fluorescence properties of Na3Gd(PO4)2:Dy3t phosphors were systematically investigated under near-UV light irradiation of 359 and 352 nm. The energy transfer efficiency (ηET) of as-prepared phosphors increases gradually from 17 to 42%, and the critical distance (Rc) between Dy3t and Tm3t ions is calculated to be 4.76 ?. For better understanding the energy transfer mechanism (ET:Dy3t →Tm3t), the decay curves were utilized on the basis of Dexter’s energy transfer formula and Reisfeld’s approximation. More importantly, the obtained CIE color coordinates of Na3Gd(PO4)2:Dy3t/Tm3t phosphors located at blue-white region under near-UV light irradiation. The results demonstrate the promising application of Na3Gd(PO4)2:Dy3t/Tm3t phosphor for near-UV white LEDs.
关键词： Citrate-gel combustion technique,Decay times-Energy transfer mechanism,Photoluminescence,White-light,Dy3t/Tm3t
更新于2025-09-16 10:30:52
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Laser-Induced Ignition and Combustion of Individual Aluminum Particles Below 10 ??m by Microscopic High-Speed Cinematography
摘要： Metal aluminum has been widely used as an ingredient in propellant, gunpowder and thermite, but there is less understanding of the combustion mechanism of aluminum particles from submicron to several microns in diameter. This paper proposes to experimentally investigate the ignition and combustion characteristics of individual aluminum particles below 10 μm. A specific in situ diagnostic experimental apparatus was first designed for directly observing the ignition and combustion behaviors of individual aluminum particles, with a submicrometer spatial resolution and a temporal resolution of tens of microseconds. Direct observation through microscopic high-speed cinematography demonstrated that, when heated by a continuous laser, individual aluminum particles thermally expanded, followed by shell rupture; the molten aluminum core overflowed and evaporated, leading to ignition and combustion. Further results showed that, when the laser power densities were gradually increased (5.88, 7.56 and 8.81 × 105 W/cm2), the durations of thermal expansion, melting and evaporation were shortened. The required time for the aluminum particles to expand to 150% of their initial diameter was shortened (34 s, 0.34 s and 0.0125 s, respectively). This study will be beneficial to further extend the investigation of other individual metal particles and reveal their combustion mechanism by direct observation.
关键词： combustion mechanism,microscopic high-speed cinematography,individual aluminum,laser ignition,submicron particle
更新于2025-09-16 10:30:52
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Uncertainty analysis of energy and economic performances of hybrid solar photovoltaic and combined cooling, heating, and power (CCHP?+?PV) systems using a Monte-Carlo method
摘要： This study examines the impacts of uncertainties in energy demands and solar resources on the energy and economic performances of hybrid solar photovoltaic and combined cooling, heating and power (CCHP + PV) systems with variations in PV penetration levels. This study investigates two models: a deterministic and stochastic model. The deterministic model uses hourly demands of the U.S. Department of Energy (DOE) reference large office building in San Francisco, CA and solar irradiance profiles in the Typical Meteorological Year (TMY) data as the independent variables. The stochastic model accounts for uncertainties in these independent variables using a Monte-Carlo method. The results show that regardless of PV penetration levels, the uncertainties in building energy demands and solar irradiance marginally influence the energy performance of CCHP + PV systems; however, they can notably increase annual operating costs up to $75,000 per year (13%). The annual cost increase is mainly attributed to a significant increase in demand charges (up to $79,000 per year). The demand charges tend to increase with higher uncertainties in the peak demand. The results suggest that in cases of the demand charge being responsible for a large portion in electricity bills (i.e., demand tariffs), a deterministic model tends to underestimate operating costs of CCHP + PV systems or other analogous distributed energy systems compared to a stochastic model. The errors with the deterministic model can become more extreme when demand charges outweigh energy charges.
关键词： Demand charge,U.S. DOE reference building,Tariff structure,Energy demand,Internal combustion engine,Combined heat and power
更新于2025-09-16 10:30:52
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Characterization of temporal variations and feedback timescales of exhaust gas recirculation gas properties using high-speed diode laser absorption spectroscopy for next-cycle control of cyclic variability
摘要： Dilute combustion offers efficiency gains in boosted gasoline direct injection engines both through knock-limit extension and thermodynamic advantages (i.e. the effect of g on cycle efficiency), but is limited by cyclic variability at high dilution levels. Past studies have shown that the cycle-to-cycle dynamics are a combination of deterministic and stochastic effects. The deterministic causes of cyclic variations, which arise from feedback due to exhaust gas recirculation, imply the possibility of using active control strategies for dilution limit extension. While internal exhaust gas recirculation will largely provide a next-cycle effect (short-timescale feedback), the feedback of external exhaust gas recirculation will have an effect after a delay of several cycles (long timescale). Therefore, control strategies aiming to improve engine stability at dilution limit may have to account for both short- and long-timescale feedback pathways. This study shows the results of a study examining the extent to which variations in exhaust gas recirculation composition are preserved along the exhaust gas recirculation flow path and thus the relative importance and information content of the long-timescale feedback pathway. To characterize the filtering or retention of cycle-resolved feedback information, high-speed (1–5 kHz) CO2 concentration measurements were performed simultaneously at three different locations along the low-pressure external exhaust gas recirculation loop of a four-cylinder General Motors gasoline direct injection engine using a multiplexed two-color diode laser absorption spectroscopy sensor system during steady-state and transient engine operation at various exhaust gas recirculation levels. It was determined that cycle-resolved feedback propagates through internal residual gases but is filtered out by the low-pressure exhaust gas recirculation flow system and do not reach the intake manifold. Intermediate variations driven by flow rate and compositional changes are also distinguished and identified.
关键词： exhaust gas recirculation,cyclic variability,nonlinear dynamics,combustion stability,Dilute combustion
更新于2025-09-12 10:27:22
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[IEEE 2019 20th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Erlagol (Altai Republic), Russia (2019.6.29-2019.7.3)] 2019 20th International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices (EDM) - Determination of the Flame Front Speed on Sensor’s Signals of Distributed Electro-Optical System
摘要： The article is devoted to the development of a method for determining of a flame speed according to signals of electro-optical flame detectors. Analytical dependencies are formulated for the calculation of the flame front speed by the time-of-flight method with the determination of the time delay by four methods: threshold method; method on the basis of the cross-correlation function; method based on the envelope correlation coefficient; method based on cross-spectral density. The results of study of the proposed methods for accuracy of the time delay determining for the simulated noisy signals and for the characteristic experimental signals obtained by recording radiation of non-stationary combustion are presented. The method based on the cross-correlation function is optimal for the implementation of the system. The influence of the analysis time range of the detector signals on the error in determining the time delay was estimated. Criteria for selecting the lower and upper boundaries of the time window were formulated. Algorithm for determining of the flame front speed from the signals of electro-optical flame detectors is proposed.
关键词： explosion suppression,Non-stationary combustion,electro-optical system,flame front speed,coal mine
更新于2025-09-12 10:27:22
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On the possibility to improve petrol engine operation by laser ignition
摘要： A typical method frequently used for the experimental investigation of engines operation at light load, low speed and different air-fuel ratios by spark timing adjustment was applied to understand in what measure the characteristics of the ignition system could improve the petrol engines performances. In this sense, a Laser Ignition - LI system replacing the original spark ignition system of the engine was mounted and some comparisons between these systems have been made based on engine power, coefficients of variation and combustion duration when 500 consecutive cycles were registered for 2000 rpm engine speed with load equivalent to 2 bar brake mean effective pressure and up to 1.25 relative air-fuel ratios.
关键词： Laser ignition of engines,Laser induced combustion,Passively Q-switched laser,Lean-fuel ignition
更新于2025-09-12 10:27:22
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EXPRESS: Two-Dimensional Temperature Measurement in a High Temperature and Pressure Combustor Using Computed Tomography Tunable Diode Laser Absorption Spectroscopy (CT-TDLAS) with a Wide-Scanning Laser at 1335–1375 nm
摘要： Tunable diode laser absorption spectroscopy (TDLAS) technology is a developing method for temperature and species concentration measurements with the features of non-contact, high precision, high sensitivity, etc. The difficulty of two-dimensional (2D) temperature measurement in actual combustors has not yet been solved because of pressure broadening of absorption spectra, optical accessibility, etc. In this study, the combination of computed tomography (CT) and TDLAS with a wide scanning laser at 1335–1375 nm has been applied to a combustor for 2D temperature measurement in high temperature of 300–2000 K and high pressure of 0.1–2.5 MPa condition. An external cavity type laser diode with wide wavelength range scanning at 1335–1375 nm was used to evaluate the broadened H2O absorption spectra due to the high temperature and high pressure effect. The spectroscopic database in high temperature of 300–2000 K and high pressure of 0.1–5.0 MPa condition has been revised to improve the accuracy for temperature quantitative analysis. CT reconstruction accuracy was also evaluated in different cases, which presented the consistent temperature distribution between CT reconstruction and assumed distributions. The spatial and temporal distributions of temperature in the high temperature and high pressure combustor were measured successfully by CT-TDLAS using the revised spectroscopic database.
关键词： high temperature and high pressure field,TDLAS,computed tomography,2D,Two-dimensional temperature measurement,combustion,CT,tunable diode laser absorption spectroscopy
更新于2025-09-12 10:27:22
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Technoeconomic assessments of hybrid photovoltaic-thermal vs. conventional solar-energy systems: Case studies in heat and power provision to sports centres
摘要： This paper presents a comprehensive analysis of the energetic, economic and environmental potentials of hybrid photovoltaic-thermal (PVT) and conventional solar energy systems for combined heat and power provision. A solar combined heat and power (S-CHP) system based on PVT collectors, a solar-power system based on PV panels, a solar-thermal system based on evacuated tube collectors (ETCs), and a S-CHP system based on a combination of side-by-side PV panels and ETCs (PV-ETC) are assessed and compared. A conventional CHP system based on a natural-gas-fired internal combustion engine (ICE) prime mover is also analysed as a competing fossil-fuel based solution. Annual simulations are conducted for the provision of electricity, along with space heating, swimming pool heating and hot water to the University Sports Centre of Bari, Italy. The results show that, based on a total installation area of 4000 m2 in all cases, the PVT S-CHP system outperforms the other systems in terms of total energy output, with annual electrical and thermal energy yields reaching 82.3% and 51.3% of the centre’s demands, respectively. The PV system is the most profitable solar solution, with the shortest payback time (9.4 years) and lowest levelised cost of energy (0.089 €/kWh). Conversely, the ETC solar-thermal system is not economically viable for the sports centre application, and increasing the ETC area share in the combined PV-ETC S-CHP system is unfavourable due to the low natural gas price. Although the PVT S-CHP system has the highest investment cost, the high annual revenue from the avoided energy bills elevates its economic performance to a level between those of the conventional PV and ETC-based S-CHP systems, with a payback time of 13.7 years and a levelised cost of energy of 0.109 €/kWh. However, at 445 tCO2/year, the CO2 emission reduction potential of the PVT S-CHP system is considerably higher (by 40–75%) than those of the all other solar systems (254–317 tCO2/year). Compared to the solar energy systems, the ICE-CHP system has the shortest payback time (6.2 years), but its CO2 emission reduction (25 tCO2/year) is significantly lower. A high carbon price is beneficial for improving the cost-competitiveness of the solar energy systems, boosting its market penetration and helping to meet any carbon emission targets.
关键词： Internal combustion engine,Cogeneration,Combined heat and power,Solar collector,CHP,PV-thermal
更新于2025-09-12 10:27:22
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A Sensitive and Reliable Carbon Monoxide Monitor for Safety-focused Applications in Coal Mine using a 2.33 μm Laser Diode
摘要： In this paper, a stable and reliable carbon monoxide (CO) monitoring system with high sensitivity (at sub-ppm level) was designed and demonstrated with particular reference to use in the mining industry, tailoring the design specifically for forecasting spontaneous combustion, a major hazard to miners. An appropriate strong CO absorption line was used to minimize the interferences expected from gases present in ambient air, with several preferred CO absorption lines selected and investigated, therefore choosing a distributed feedback (DFB) laser operating at a wavelength of 2330.18 nm as the excitation source. Through a detailed investigation, a minimum detection limit of ~0.2 ppm and a measurement precision of <50 ppb were achieved with a 1 s averaging time. Further long-term continuous monitoring evaluation was carried out, demonstrated the excellent stability and reliability of the developed CO monitor. The results obtained have validated the potential of this design of a CO monitoring system for practical monitoring applications underground to enhance safety in the mining industry.
关键词： mining industry,carbon monoxide,forecasting spontaneous combustion,direct absorption spectroscopy
更新于2025-09-12 10:27:22
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Multi-functional lasers
摘要： NASA and rocket manufacturer Virgin Orbit have partnered to 3D print a combustion chamber that could be used in rockets carrying small satellites to space. The companies aimed to create a 3D printed copper alloy combustion chamber with multiple materials more quickly than conventional methods. The chamber was printed using NASA additive copper alloy, GRCop-84, with a second bimetallic super-alloy layer which was applied using Virgin Orbit’s hybrid additive/subtractive machine. In tests using high-pressure liquid oxygen/kerosene propellants, the chamber delivered more than 2,000 pounds of thrust successfully in nearly two-dozen, 60-second test firings.
关键词： additive manufacturing,NASA,Virgin Orbit,3D printing,rocket combustion chamber
更新于2025-09-12 10:27:22