Browse Topic: Spectroscopy

Items (272)
Are Internal Diesel Injector Deposits (IDID) Mainly Linked to Biofuel Chemical Composition or/and Engine Operation Condition?2019-01-00611/15/2019
The increased use of alternative fuels has been linked to performance deterioration of injectors and engines as a result of internal diesel injector deposits (IDID). The present paper investigates fuel composition impact on injector tendency to blockage. Three main areas were investigated : (1) deposits linked to paraffins and aromatics content; (2) deposits linked to biodiesel composition using fatty acid methyl esters (FAME) and hydrotreated vegetal oil (HVO); and (3) deposits linked to the presence of additives (Dodecenylsuccinic anhydride DDSA, Dodecenyl Succinimid DDSI and Sodium Naphthenate). A deposit formation method was developed for the injection bench in order to discriminate the impact of fuels on system performance in terms of fuel volume injected, injection duration and stability. Three operation conditions were tested to represent low, intermediate and high load. In addition, the influence of soaking time and injector heating temperature was evaluated. The nature of the deposit was studied based on its morphology and chemical composition determined using Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) Spectroscopy. Deposits were observed for all fuels, even the highly paraffinic biofuel like HVO. Two main results are presented: Firstly, the main impact of fuel soaking period and high load operation on the occurrence of IDID, it was observed that deposit formation can be controlled by the time the fuel remains in contact with the hot metallic surface of the injector; Secondly, the complex correlation between deposit nature and characteristics and the injector’s tendency to blockage, for example, there is no straightforward link between deposit thickness and injector blockage, other parameters seem to be more appropriate to predict injector blockage. These are discussed in more detail in this study.
Alves Fortunato, MairaLenglet, FrancisBen Amara, ArijStarck, Laurie
A Novel Battery Impedance Model Considering Internal Temperature Gradient2018-01-04364/3/2018
Battery models are often applied to describe the dynamic characteristics of batteries and can be used to predict the state of the battery. Due to the process of charging and discharging, the battery heat generation will cause the inhomogeneity between inner battery temperature and surface temperature. In this paper, a novel battery impedance model, which takes the impact of the battery internal temperature gradient on battery impedance into account, is proposed to improve the battery model performance. Several experiments are designed and conducted for pouch typed battery to investigate the electrochemical impedance spectroscopy (EIS) characteristics with the artificial temperature gradient (using a heating plate). Experimental results indicate that the battery internal temperature gradient will influence battery EIS regularly. Using the experimental result without temperature gradient, and with the parameter identification based on particle swarm optimization (PSO), the relationship between impedance and temperature is founded. To obtain the more accurate parameter of battery impedance model considering the influence temperature gradient, we discretize the battery into several slices, which are connected in parallel. The impedance of the entire battery is deemed as the combination of the impedance of each slice. The proposed model is validated with experiments, and the results show that the calculated EIS from the battery model considering the temperature gradient show good accordance to the experimental values and the maximum absolute error is 0.31mΩ, which indicates that, the proposed battery model is a promising alternative for engineering application use.
Jiang, BoDai, HaifengZhu, Jiangong
Battery Impedance Measurement with Step Current of Different Amplitude under Temperature and State of Charge Control2018-01-04434/3/2018
Electrochemical Impedance Spectroscopy (EIS) is often applied to analyze and describe the battery internal electrochemical processes. And the methods of battery state estimation including state of health diagnosis with electrochemical impedance have attracted a wide attention. In the paper, a novel fast impedance measuring method based on wavelet transform with a step excitation current is proposed and further studied. With the method, the current generated by the electric vehicle and the responding voltage of the battery can be utilized to calculate and provide the battery impedance for the battery management system. Taking into account the varying amplitude of the current and the battery states, the battery impedance was measured with step excitation signals of different amplitude at different temperature and state of charge (SOC). Then the battery impedance was calculated with the proposed method and compared to the electrochemical impedance measured with an electrochemical workstation. It is observed that the impedance in the mid high frequency range (>10 Hz) greatly related to changes of the internal processes and properties caused by the aging process is weakly affected by the varying signal amplitude. And the effect is limited and can be neglected at high temperature (>25 °C). SOC also has little effect on the impedance in the frequency range higher than 10 Hz. It benefits the state of health diagnosis with the impedance in the frequency range. Accordingly, a state of health diagnosis method based on the impedance calculated with the wavelet transform is proposed in the end.
Wang, XueyuanZhang, JunhanWei, XuezheDai, Haifeng
Characterization and Discrimination of Aircrafts and Runways Winter Maintenance Anti-Icing Fluids2017-01-21409/19/2017
Aircrafts and runways de-icing operations with anti-icing fluids are still the most commonly used methods. In the specific case of aircrafts, they do contain glycols. Nevertheless, since two decades now, major environmental concerns are raised, along with important associated costs. Furthermore, once applied either on aircrafts or on runways, these fluids are diluted because of water brought from adverse weather conditions (rain, snow, icy conditions), conducting to increasing the freezing point from a subzero level to 0°C. The characterization of the freezing points of these fluids is indeed crucial for safety reasons. For years now, Raman spectroscopy is used for the characterization of these fluids, specifically the freezing point. But the presence of dyes did perturb the usual spectroscopic characterization. Three fluids, from their pure commercial form to highly diluted rate, were then studied by means of Raman spectroscopy at a new laser wavelength, and with the support of multivariate data analysis (MDA). Each fluid belonged to a specific type of aircraft anti-icing fluid (I, II and IV). The discrimination of the fluids between each other was obtained. Spectroscopic data was organized through MDA in such a way that neither the presence of a dye nor the dilution would allow any confusion. The identification of the evolution of freezing temperatures with dilution was elaborated, with their rapid increase as dilution increased too. MDA allowed also the elaboration of prediction models, and such tool conducted to the forecast of concentration in anti-icing, or of its freezing temperature on the basis of the Raman signature of the considered fluid, with a given degree of confidence.
Marchetti, MarioCasteran, GuillaumeJobard, CelineSaintot, BrunoBourson, PatriceFontana, Marc
Gas sensors are usually engineered to detect a specific molecule in one of many potential categories: toxic gases, combustible gases, and VOCs. A number of technologies, such as infrared, photoionization, catalytic, and electrochemical, are used to test for differing molecular species. Each method has specifications for resolution, sensitivity, temperature, and humidity range. Gas sensors are most useful when they have high sensitivity and flexibility in the gases they can detect.
Development of Photoacoustic Sensing Platforms17AERP06_116/1/2017
Research focuses on sensor miniaturization and detection of chemical targets both proximally and at range. Army Research Laboratory, Adelphi, Maryland In recent years, photoacoustic spectroscopy (PAS) has emerged as an attractive and powerful technique well suited for sensing applications. The development of high- power radiation sources and more sophisticated electronics, including sensitive microphones and digital lock-in amplifiers, have allowed for significant advances in PAS. Furthermore, photoacoustic (PA) detection of IR absorption spectra using modern tunable lasers offers several advantages, including simultaneous detection and discrimination of numerous molecules of interest. Successful applications of PAS in gases and condensed matter have made this a notable technique and it is now studied and employed by scientists and engineers in a variety of disciplines. PAS is a detection technique under the umbrella of photothermal spectroscopy. Photothermal spectroscopy encompasses a group of highly sensitive methods that can be used to detect trace levels of optical absorption and subsequent thermal perturbations of the sample in gas, liquid, or solid phases. The underlying principle that connects these various spectroscopic methods is the measurement of physical changes (i.e., temperature, density, or pressure) as a result of a photo-induced change in the thermal state of the sample. Other photothermal techniques include photothermal interferometry (PTI), photothermal lensing (PTL), and photothermal deflection (PTD).
Surface Functional Groups and Graphitization Degree of Soot in the Sooting History of Methane Premixed Flame2017-01-10033/28/2017
The evolution of surface functional groups (SFGs) and the graphitization degree of soot generated in premixed methane flames are studied and the correlation between them is discussed. Test soot samples were obtained from an optimized thermophoretic sampling system and probe sampling system. The SFGs of soot were determined by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) after removing the soluble impurities from the soot samples, while the graphitization degree of soot was characterized by Raman spectrum and electron energy loss spectroscopy (EELS). The results reveal that the number of aliphatic C-H groups and C=O groups shows an initial increase and then decrease in the sooting history. The large amount of aliphatic C-H groups and small amount of aromatic C-H groups in the early stage of the soot mass growth process indicate that aliphatic C-H groups make a major contribution to the early stage of soot mass growth. The higher graphitization degree of soot appears at low height above the burner when the graphite core is formed. The graphitization degree of soot rapidly decreases in the early mass growth stage then increases in the maturation process. The results from transmission electron microscopy (TEM), SFGs, and the graphitization degree verify the assumption that the nascent soot consists of a graphite-like core and an aliphatic shell. There is a strong correlation between SFGs and graphitization degree in the early stage of the soot mass growth process. During the soot maturation process, the correlation between SFGs and graphitization degree weakens. The SFGs may be related to the aggregate soot particle properties, such as fractal dimension.
Liu, YeLv, GangFan, ChenyangLi, NaWang, Xiaowei
Silicon Based Mid-Infrared SiGeSn Heterostructure Emitters and Detectors17AERP02_072/1/2017
Enhancing the performance of GeSn p-i-n photodiodes using gold metal nanostructures. Air Force Research Laboratory, Arlington, Virginia The goal of this research project was to advance the science and technology of silicon-based photonic devices using SiGeSn heterostructures. Such devices work in mid-IR spectral range and form the foundation for mid-IR photonics that enable on-chip systems for applications ranging from vibrational spectroscopy, chem/bio sensing, medical/health uses, to environmental monitoring. This project was mostly directed toward improving GeSn detectors with the use of surface plasmons induced by carefully designed metal nanostructures. The goal was to replace the current mid-IR detectors that are usually photodiodes made from narrow bandgap III-V or II-VI semiconductor compounds such as InGaAs, InSb, HgCdTe (MCT) or type-II InGaAs/InGaSb superlattice. These photodiodes are incompatible with the CMOS process and cannot be easily integrated with Si electronics. The GeSn mid-IR detectors developed in this project are fully compatible with the CMOS process. Beginning with GeSn-based p-i-n photodiodes with an active GeSn layer that is almost fully strained, the strategy is to use the surface plasmon effect to enhance the optical field in the GeSn active region, which leads to increased absorption of incident photons and creates electron-hole pairs that contribute to the electric current that can be detected. Specifically, the use of a gold metal film perforated with a two-dimensional subwavelength hole array as the plasmonic structure to be deposited on top of the GeSn p-i-n photodetector was considered. Such structures are capable of producing enhanced optical fields under the illumination of some wavelengths residing in its surface plasmon resonance range. They have been used to improve the performance of quantum dot infrared photodetectors (QDIPs). Increased photocurrent and detection wavelength selection have been demonstrated.
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