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Terahertz time-domain spectroscopy of high-pressure flames
Jason BASSI, Mark STRINGER, Bob MILES, Yang ZHANG
Front Energ Power Eng Chin. 2009, 3 (2): 123-133.
https://doi.org/10.1007/s11708-009-0033-x
Laser spectroscopy in the visible and near infrared is widely used as a diagnostic tool for combustion devices, but this approach is difficult at high pressures within a sooty flame itself. High soot concentrations render flames opaque to visible light, but they remain transparent to far-infrared or terahertz (THz) radiation. The first far-infrared absorption spectra, to the best of our knowledge, of sooty, non-premixed, ethylene high-pressure flames covering the region of 0.2-2.5 THz is presented. A specially designed high-pressure burner which is optically accessible to THz radiation has been built allowing flame transmission measurements up to pressures of 1.6 MPa. Calculations of the theoretical combustion species absorption spectra in the 0.2-3 THz range have shown that almost all the observable features arise from H2O. A few OH (1.84 and 2.51 THz), CH (2.58 THz), and NH3 (1.77 and 2.95 THz) absorption lines are also observable in principle. A large number of H2O absorption lines are observed in the ground vibrational in a laminar non-premixed, sooty flame (ethylene) at pressures up to 1.6 MPa.
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Fuel variability effect on flickering frequency of diffusion flames
Jizhao LI, Yang ZHANG
Front Energ Power Eng Chin. 2009, 3 (2): 134-140.
https://doi.org/10.1007/s11708-009-0034-9
It is known that fuel variability of different gas suppliers may cause combustion instability in a gas turbine combustor. Mechanisms that control the time scale of the heat release oscillations and acoustic pressure perturbations are both physical and chemical in nature, and thus can be influenced by changes in fuel composition. The intent of this study is to investigate the fuel variability on the flickering frequency of diffusion flames in the hope of understanding some of the fundamental aspects of fuel variability effect on the dynamics of combustion. Experiments were conducted at atmospheric pressure with a matrix of methane and propane blends. An optical fibre system was applied to capture simultaneously the flame flickering at two different light frequencies (430 nm and 516 nm), which provided a means of comparing the chemistry change. It was found that the low frequency oscillation of flow and flame structures depended only weakly on the exit velocities of the fuel, while ambient conditions had a significant effect on flickering frequencies and spectrum. The results of using CH4 and C3H8 as test fuels at different flow rates showed very little variations, with peak frequencies at 11-13 Hz. When the jet flame was not disturbed, harmonics to at least the third mode were obtained in most of these cases. However, the cases which included CH4/C3H8 splits of 90/10, 85/15 and 80/20 by volume showed that unstable flickering frequencies and flame harmonics were not observed. When a mixture of methane/propane at a ratio of 1:1 was used the peak flickering frequency was around 6 Hz, and slight disturbance in the environment would cause the harmonics to disappear. Mechanisms thought to produce changes in the dynamic response and frequency harmonics were discussed.
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Thin-liquid-film evaporation at contact line
Hao WANG, Zhenai PAN, Zhao CHEN
Front Energ Power Eng Chin. 2009, 3 (2): 141-151.
https://doi.org/10.1007/s11708-009-0020-2
When a liquid wets a solid wall, the extended meniscus near the contact line may be divided into three regions: a nonevaporating region, where the liquid is adsorbed on the wall; a transition region or thin-film region, where effects of long-range molecular forces (disjoining pressure) are felt; and an intrinsic meniscus region, where capillary forces dominate. The thin liquid film, with thickness from nanometers up to micrometers, covering the transition region and part of intrinsic meniscus, is gaining interest due to its high heat transfer rates. In this paper, a review was made of the researches on thin-liquid-film evaporation. The major characteristics of thin film, thin-film modeling based on continuum theory, simulations based on molecular dynamics, and thin-film profile and temperature measurements were summarized.
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A new miniaturized engine based on thermomagnetic effect of magnetic fluids
Lujun ZHOU, Yimin XUAN, Qiang LI, Wenlei LIAN
Front Energ Power Eng Chin. 2009, 3 (2): 160-166.
https://doi.org/10.1007/s11708-009-0018-9
A new engine system, essentially consisting of a permanent NdFeB magnet, a kerosene-based magnetic fluid and a rotor, is proposed based on the thermomagnetic effect of a temperature-sensitive magnetic fluid. The rotor was driven by the thermal convection of the magnetic fluid in the presence of a homogeneous external magnetic field. A digital camera was used to record the rotation speed of the rotor to investigate the performance of the engine system under varying conditions such as heat load, heat sink temperature, and magnetic field distribution. The peak angle velocity obtained for the rotor was about 2.1 rad/min. The results illustrate that the rotation speed of the rotor increases as the input heat load increases, or as the heat sink temperature decreases. The performance of the motor is considerably influenced by the magnetic field imposed. Therefore, the performance of such an engine can be controlled conveniently by changing the external magnetic field and/or the temperature distribution in the fluid.
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Experimental study of critical flow of water at supercritical pressure
Yuzhou CHEN, Chunsheng YANG, Shuming ZHANG, Minfu ZHAO, Kaiwen DU, Xu CHENG
Front Energ Power Eng Chin. 2009, 3 (2): 175-180.
https://doi.org/10.1007/s11708-009-0029-6
Experimental studies of the critical flow of water were conducted under steady-state conditions with a nozzle 1.41 mm in diameter and 4.35 mm in length, covering the inlet pressure range of 22.1-26.8 MPa and inlet temperature range of 38-474°C. The parametric trend of the flow rate was investigated, and the experimental data were compared with the predictions of the homogeneous equilibrium model, the Bernoulli correlation, and the models used in the reactor safety analysis code RELAP5/MOD3.3. It is concluded that in the near or beyond pseudo-critical region, thermal-dynamic equilibrium is dominant, and at a lower temperature, choking does not occur. The onset of the choking condition is not predicted reasonably by the RELAP5 code.
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Typical off-design analytical performances of internal combustion engine cogeneration
Xiaohong HE, Ruixian CAI
Front Energ Power Eng Chin. 2009, 3 (2): 184-192.
https://doi.org/10.1007/s11708-009-0007-z
Based on experimental data, typical off-design characteristic curves with corresponding formulas of internal combustion engine (ICE) are summarized and investigated. In combination with analytical solution of single-pressure heat recovery steam generator (HRSG) and influence of ambient pressure on combined heat and power (CHP) system, off-design operation regularities of ICE cogeneration are analyzed. The approach temperature difference ΔTa , relative steam production and superheated steam temperature decrease with the decrease in engine load. The total energy efficiency, equivalent exergy efficiency and economic exergy efficiency first increase and then decrease. Therefore, there exists an optimum value, corresponding to ICE best efficiency operating condition. It is worth emphasizing that ΔTa is likely to be negative in low load condition with high design steam parameter and low ICE design exhaust gas temperature. Compared with single shaft gas turbine cogeneration, ΔTa in ICE cogeneration is more likely to be negative. The main reason for this is that the gas turbine has an increased exhaust gas flow with the decrease in load; while ICE is on the contrary. Moreover, ICE power output and efficiency decrease with the decrease in ambient pressure. Hence, approach temperature difference, relative steam production and superheated steam temperature decrease rapidly while the cogeneration efficiencies decrease slightly. It is necessary to consider the influence of ambient conditions, especially the optimization of ICE performances at different places, on cogeneration performances.
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16 articles
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