Thermal performance of a micro-combustor for micro-gas turbine system

Premixed combustion of hydrogen gas and air was performed in a stainless steel based micro-annular combustor for a micro-gas turbine system. Micro-scale combustion has proved to be stable in the micro-combustor with a gap of 2 mm. The operating range of the micro-combustor was measured, and the maximum excess air ratio is up to 4.5. The distribution of the outer wall temperature and the temperature of exhaust gas of the micro-conbustor with excess air ratio were obtained, and the wall temperature of the micro-combustor reaches its maximum value at the excess air ratio of 0.9 instead of 1 (stoichiometric ratio). The heat loss of the micro-combustor to the environment was calculated and even exceeds 70% of the total thermal power computed from the consumed hydrogen mass flow rate. Moreover, radiant hunt transfer covers a large fraction of the total heat loss. Measures used to reduce the heat loss were proposed to improve the thermal performance of the micro-combustor. The optimal operating status of the micro-combustor and micro-gas turbine is analyzed and proposed by analyzing the relationship of the temperature of the exhaust gas of the micro-combustor with thermal power and excess air ratio. The investigation of the thermal performance of the micro-combustor is helpful to design an improved microcombustor.

Spatial resolved temperature measurement based on absorption spectroscopy using a single tunable diode laser

A novel method based on wavelength-multiplexed line-of-sight absorption and profile fitting for non-uniform flow field measurement is reported. A wavelength scanning combing laser temperature and current modulation WMS scheme is used to implement the wavelength-multiplexed-profile fitting method. Second harmonic (2f) signal of eight H2O transitions features near 7,170 cm(-1) are measured in one period using a single tunable diode laser. Spatial resolved temperature distribution upon a CH4/air premixed flat flame burner is obtained. The result validates the feasibility of strategy for non-uniform flow field diagnostics by means of WMS-2f TDLAS.

Extinction of lean near-limit methane/air flames at elevated pressures under normal- and reduced-gravity

perimentally at evaluated pressures and under normal- and micro-gravity conditions utilizing the 3.5 s drop tower of the National Microgravity Laboratory of China. The results showed that under micro-gravity conditions the natural convection is minimized and the flames become more planar and symmetric compared to normal gravity. In both normal- and micro-gravity experiments and for a given strain rate and fuel concentration, the flame luminosity was found to enhance as the pressure increases. On the other hand, at a given pressure, the flame luminosity was determined to weaken as the strain rate decreases. At a given strain rate, the fuel concentration at extinction was found to vary non-monotonically with pressure, namely it first increases and subsequently decreases with pressure. The limit fuel concentration peaks around 3 and 4 atm under normal- and micro-gravity, respectively. The extinction limits measured at micro-gravity were in good agreement with predictions obtained through detailed numerical simulations but they are notably lower compared to the data obtained under normal gravity. The simulations confirmed the non-monotonic variation of flammability limits with pressure, in agreement with previous studies. Sensitivity analysis showed that for pressures between one and 5 atm, the near-limit flame response is dominated by the competition between the main branching, H + O2 ? OH + O, and the pressure sensitive termination, H+O2+M? HO2 + M, reaction. However, for pressures greater than 5 atm it was determined that the HO2 kinetics result in further chain branching in a way that is analogous to the third explosion limit of H2/O2 mixtures. 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

近贫燃极限甲烷/空气火焰的层流燃烧速度研究

利用微重力条件下向外传播的球形火焰,对贫燃极限附近甲烷/空气预混火焰的层流燃烧速度进行了测量,得到当量比从0.512(本文微重力实验中测定的可燃极限)到0.601范围内的零拉伸层流燃烧速度,并与前人实验数据和使用3种化学反应动力学模型的计算结果进行了比较. 本文实验结果与已有的微重力实验数据非常接近,而其他研究者在常重力实验中得到的数据大多都明显高于微重力实验结果. 不同化学反应机理预测的燃烧速度比微重力实验测量值大得多,这是因为它们主要是用远离可燃极限的燃烧速度校核的

加压条件下甲烷/空气预混火焰可燃极限的微重力实验研究

本文成功搭建了适用于中国科学院力学研究所国家微重力实验室(NMLC)落塔的高压对冲火焰实验系统, 并首次开展了微重力条件下加压对冲火焰实验, 测定了一定张力条件下甲烷/空气层流预混火焰的熄灭极限. 实验结果表明, 随着压力的增高, 甲烷/空气混合气体的可燃极限呈先增后降的非单调变化趋势, 峰值发生在0.4 MPa左右. 浮力对加压下微弱火焰熄灭极限的影响明显, 在常重力条件下, 相同张力下的熄灭极限较微重力条件下的偏大, 峰值出现的压力略低. 微重力条件下的实验结果与使用CHEMKIN的数值模拟的结果相当一致.