Active control of combustion oscillations in a lean premixed gas-turbine combustor

Active control of combustion oscillations occurring in a methane-air lean premixed model combustor is accomplished by the method of secondary fuel injection. The main flame is sustained by an axial vane swirler. The central part of the swirler is endowed a function as the secondary fuel injector. The fuel jets from the injector enhance the flame stability by producing rich stable flames in the region of the flame base. Open-loop controls by secondary fuel injection with constant flow rates have been conducted on a naturally unstable condition. The results show sensitivity to the injection amount. It indicates that the flame base is very sensitive to the additional fuel distribution. A similar discussion is made on NOx emission also. Finally, a closed-loop control has been performed by implementing the mixed H-2/H-infinity controller. An obvious effect of the closed-loop control on the suppression of pressure oscillations is found without loosing an advantage for low NOx emissions

Isotropic Seebeck coefficient of aligned single-wall carbon nanotube films

How the morphology of a macroscopic assembly of nanoobjects affects its properties is a long-standing question in nanomaterials science and engineering. Here, we examine how the thermoelectric properties of a flexible thin film of carbon nanotubes depend on macroscopic nanotube alignment. Specifically, we have investigated the anisotropy of the Seebeck coefficient of aligned and gated single-wall carbon nanotube thin films. We varied the Fermi level in a wide range, covering both theﾠp-type andﾠn-type regimes, using electrolyte gating. While we found the electrical conductivity along the nanotube alignment direction to be several times larger than that in the perpendicular direction, the Seebeck coefficient was found to be fully isotropic, irrespective of the Fermi level position. We provide an explanation for this striking difference in anisotropy between the conductivity and the Seebeck coefficient using Mott's theory of hopping conduction. Our experimental evidence for an isotropic Seebeck coefficient in an anisotropic nanotube assembly suggests a route toward controlling the thermoelectric performance of carbon nanotube thin films through morphology control

Synthesis and optical properties of WS2 nanotubes with relatively small diameters

Abstract Tungsten disulfide (WS2) nanotubes exhibit various unique properties depending on their structures, such as their diameter and wall number. The development of techniques to prepare WS2 nanotubes with the desired structure is crucial for understanding their basic properties. Notably, the synthesis and characterization of multi-walled WS2 nanotubes with small diameters are challenging. This study reports the synthesis and characterization of small-diameter WS2 nanotubes with an average inner diameter of 6 nm. The optical absorption and photoluminescence (PL) spectra of the as-prepared nanotubes indicate that a decrease in the nanotube diameter induces a red-shift in the PL, suggesting that the band gap narrowed due to a curvature effect, as suggested by theoretical calculations