乙醇在微尺度双电极燃烧器内的燃烧特性研究

发布时间：2018-08-31 08:07

【摘要】：随着微机电系统的发展,微燃烧器的研制逐渐成为当今的热点课题之一。基于燃烧的微动力系统,凭借其能量密度高、污染排放小等优点,逐渐成为替代化学电池的理想方案之一。但燃烧器体积的减小,也带来了许多诸如表面积/体积比较大,燃料停留时间短、散热损失较大、难以维持稳定燃烧等难题。液体燃料的雾化燃烧是提升燃料利用率的重要途径之一。传统方法多以机械雾化为主,而对燃料进行荷电雾化燃烧是改进微燃烧器性能的可行方法。采取喷嘴-网格的单电极结构和喷嘴-环形电极-网格的双电极结构,设计制作微型燃烧器,并以双电极结构为基础设计催化燃烧器。以乙醇为燃料,对燃烧器内雾化及燃烧特性进行实验研究,并分析雾化对燃烧的影响因素,研究电场的变化对雾化燃烧的影响。研究表明,在单、双两种电极结构下,乙醇荷电雾化均会出现脉动、锥-射流、偏移射流以及多股射流四种雾化模式。其中,锥-射流模式下喷雾粒径分布最为均匀,多股射流模式下喷雾粒径平均尺寸最小。单电极燃烧器内,喷雾粒径范围为8-28.8μm,双电极燃烧器内,喷雾粒径范围为2.3-17μm。双电极结构下,喷雾荷质比稳定在较低值,而单电极结构下荷质比呈上升趋势,二者均在锥-射流模式下荷质比相对稳定。环形电极的加入使乙醇荷电方式发生变化,提升了雾化效果,并在锥-射流模式和多股射流模式下达到最佳。在燃烧过程中,双电极燃烧器内火焰呈现淡蓝色,催化燃烧器内呈无焰燃烧,表明其乙醇完全燃烧程度较高。环形电极的加入使火焰稳燃极限拓宽,燃烧器可在更大的乙醇流量范围以及更宽的当量比范围内工作。双电极燃烧器内,乙醇在锥-射流模式下火焰温度最高,多股射流模式次之。粒径的减小加快了液滴蒸发速率,使得乙醇蒸气与空气预混时间增加,相对延长了燃料的停留时间提升了燃烧器的稳定性。粒径较大的液滴由雾化区到燃烧区的行进过程中,部分液滴由于未完全蒸发而到达火焰处,增加了散热损失,因此在雾化效果好的双电极燃烧器内乙醇燃烧效率较高,锥-射流模式下燃烧效率高于其他雾化模式。催化网格的加入促进了乙醇在高温下的分解及氧化,并减少了有害尾气排放量。乙醇燃烧效率在双电极燃烧器内可达90.5%,催化燃烧器内可达94.5%。环形电极的加入对提升乙醇雾化效果作用明显,催化网格对于燃烧效率有较大提升,可通过外加电场参数的优化来提升荷电喷雾微燃烧器的性能。
[Abstract]:With the development of MEMS, the development of micro-burner has become one of the hot topics. Because of its advantages of high energy density and low pollution emission, the combustion micro-power system has become one of the ideal alternatives for chemical batteries. However, the reduction of burner volume also brings many problems such as large surface area / volume ratio, short residence time of fuel, large heat loss and difficult to maintain stable combustion. The atomization combustion of liquid fuel is one of the important ways to improve the fuel efficiency. The traditional methods are mostly mechanical atomization, but charge atomization combustion is a feasible method to improve the performance of micro combustor. The single electrode structure of nozzle-grid and the double electrode structure of nozzle-ring electrode-grid are adopted to design and manufacture micro burner and to design catalytic burner based on double electrode structure. The atomization and combustion characteristics in the burner were studied experimentally with ethanol as fuel. The influence factors of atomization on combustion and the influence of electric field on atomization combustion were analyzed. The results show that there are four kinds of atomization modes of ethanol charge atomization, such as pulsation, cone-jet, offset jet and multi-jet. The spray particle size distribution is the most uniform in the cone-jet mode and the smallest in the multi-jet mode. The spray particle size ranges from 8-28.8 渭 m in a single-electrode burner to 2.3-17 渭 m in a dual-electrode burner. Under the double electrode structure, the ratio of charge to mass is stable at a lower value, while the ratio of charge to mass of a single electrode structure is on the rise. Both of them are relatively stable in the cone-jet mode. The addition of ring electrode changes the charged mode of ethanol, and improves the atomization effect, and achieves the best results in the cone-jet mode and multi-jet mode. In the combustion process, the flame in the two-electrode burner is light blue, and the combustion in the catalytic burner is flameless, which indicates that the complete combustion degree of ethanol is high. With the addition of ring electrode, the flame stability limit is widened, and the burner can work in a wider range of ethanol flow rate and wider equivalent ratio. In the two-electrode burner, the flame temperature of ethanol is the highest in the cone-jet mode, followed by the multi-jet mode. The decrease of particle size accelerates the evaporation rate of liquid droplets, increases the premixing time of ethanol vapor and air, and prolongs the residence time of fuel to improve the stability of the burner. In the process of moving from atomization zone to combustion zone, some droplets reach the flame due to incomplete evaporation, which increases the heat loss, so the ethanol combustion efficiency is higher in the two-electrode burner with good atomization effect. The combustion efficiency in cone-jet mode is higher than that in other atomization modes. The addition of catalytic meshes promoted the decomposition and oxidation of ethanol at high temperature and reduced the harmful tail gas emissions. The combustion efficiency of ethanol is 90.5 in the double electrode burner and 94. 5 in the catalytic burner. The effect of ring electrode on ethanol atomization is obvious, and the catalytic mesh can improve the combustion efficiency greatly. The performance of charged spray micro-burner can be improved by the optimization of applied electric field parameters.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK16

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