جستجوی مقالات مرتبط با کلیدواژه « optical » در نشریات گروه « فنی و مهندسی »

Better performance and the regulatory requirements concerning combustion emissions have caused downsized GDI engines and consideration of strategies for improving in-cylinder mixture preparation. The sprays characteristics of the fuel injectors of GDI engines have been widely investigated by researchers. The interest in studying the characteristics of the spray is due to a strong relationship with the subsequent combustion reaction and thus with the engine's thermal efficiency. This paper analyzes the mixture formation of the spray employing an experimental laser apparatus that was used to measure the spray penetration in a constant volume chamber (CVC) and simulations performed by the fast response CFD CONVERGE software. The fuel injector used in the tests was a six-hole direct injection injector with iso-octane fuel. The measurements were taken 100 mm downstream from the injector tip along the axis with 20 MPa injection pressure. During experiments, it was observed that spray development is not symmetrical with the vertical axis, and with decreasing chamber pressure, it develops faster. Moreover, the average spray development velocities in simulations are in good agreement with experimental results.

Copper oxide thin layers were elaborated using the sol-gel dip-coating. The thickness effect on morphological, structural, optical and electrical properties was studied. Copper chloride dihydrate was used as precursor and dissolved into methanol. The scanning electron microscopy analysis results showed that there is continuity in formation of the clusters and the nuclei with the increase of number of the dips. X-ray diffractogram showed that all the films are polycrystalline cupric oxide CuO phase with monoclinic structure with grain size in the range of 30.72 - 26.58 nm. The obtained films are clear blackin appearance, which are confirmed by the optical transmittance spectra. The optical band gap energies of the deposited films vary from 3.80 to 3.70 eV. The electrical conductivity of the films decreases from 1.90.10-2 to 7.39.10-3 (Ω.cm)-1

Visible Light Communication (VLC) has emerged as a powerful technique for wireless communication systems. Providing high data rate and increasing capacity are the major problems in VLC. Recent evidence suggests that Multiple Input Multiple Output (MIMO) technique can offers improved data rates and increased link range. This paper describes the design and implementation of visible light communication system in indoor environment exploring the benefits of MIMO. The specific objective of this research was to implement a 4×4 Multiple Input (LEDs) Multiple Output (photodetectors)-VLC communication system, where a 16 white power LEDs in four arrays are setting up at transmitter and four RX modules are setting up at receiver side without the need for additional power or bandwidth as well as analyze a mathematical model for a VLC- 4×4 MIMO with different modes such as the suitable angles to cover the entire room. The research designs practically an electronic circuit for the transmitter and receiver with inexpensive components. The power distribution of different propagation modes is calculated for Single Input Single Output (SISO) and MIMO channels in typical room dimensions. The results in this paper indicate that the power is distributed uniformly for entire room when implemented VLC-MIMO as compared to VLC-SISO. Furthermore, a 4×4 MIMO implementing VLC is compared in term of BER vs. SINR with SISO communication system for both Line of Sight (LOS) and Non Line of Sight (NLOS) propagation modes. Comparing the two results of LOS and NLOS, it can be seen that a 4×4 MIMO implementing VLC for LOS perform better than the same system with NLOS due to decreasing in the received power resulted from the multipath effect.

Spectroscopic ellipsometry is a powerful technique for determining optical properties of any thin surface. A method for characterizing optical properties of warm asphalt binder using spectroscopic ellipsometry along with associated results has been presented in this paper. Thin films of warm asphalt binders were produced using LEADCAP and Sasobit and characterized using a variable angle spectroscopic ellipsometry. Refractive index and extinction coefficient of each of the samples (original and aged) were extracted from model fitted spectra. Clear variation in refractive index and extinction coefficient was observed among the samples before and after aging. The samples were found to be highly reflective with refractive index ‘n’ in the range 1.55–1.62 and extinction coefficient ‘k’ in the range of 0.01–0.06, both before and after aging. Reflectivity of PG 64-22 with LEADCAP exhibited the highest refractive index and the lowest extinction coefficient in visible wavelength of light among the samples. The results indicated that the highest reflection of visible light can be observed from LEADCAP-modified binder. Cracking properties and absorption coefficient of the binders are observed to have a correlation. The method reported here can be applied to any type of asphalt binder to determine its light absorption and reflection characteristics for a wide range of wavelength.

The work involved a fundamental study of auto-ignition under unusually high knock intensities for an optical spark ignition engine. The single-cylinder research engine adopted included full bore overhead optical access capable of withstanding continuous peak in-cylinder pressures of up to 150bar. A heavy knock was deliberately induced under relatively low loads using inlet air heating and a primary reference fuel blend of reduced octane rating. High-speed chemiluminescence natural light imaging was used together with simultaneous heat release analysis to evaluate the combustion events. Multiple centered auto-ignition events were regularly observed to lead into violent knocking events, with knock intensities above 140 bar observed. The ability to directly image the events associated with such a high magnitude of knock is believed to be a world-first in an optical engine. The multiple centered events were in good agreement with the developing detonation theory proposed elsewhere to be the key mechanism leading to heavy knock in modern downsized SI engines. The accompanying thermodynamic analysis indicated a lack of relation between knock intensity and the remaining unburned mass fraction burned at the onset of the auto-ignition. Spatial analysis of the full series of images captured demonstrated the random location of the initial auto-ignition sites, with new flame kernels forming at these sites and initially growing steadily and suppressing further growth of the main flame front before violent detonation at speeds well over the imaging frequency of the camera.