【作者】 杨帆；

【导师】 袁远；

【作者基本信息】 哈尔滨工业大学 ， 动力工程及工程热物理， 2023， 硕士

【摘要】 化石燃料在一次能源消费量中的占比巨大,但化石燃料的燃烧会产生大量大气污染物,其中的烟黑颗粒会显著影响气候变化和人体健康。乙烯是大分子烃类燃料燃烧和热裂解过程中的重要中间产物,也是烟黑颗粒的重要前驱物。电场辅助燃烧技术作为一种高效的燃烧过程控制手段被广泛关注。为了加深对化石燃料烟黑生成特性的理解,探究外加电场对扩散火焰燃烧特性的影响,本文使用数值方法对乙烯燃烧及烟黑生成进行研究。本文以乙烯燃料为研究对象,对乙烯层流扩散火焰的烟黑生成特性以及外加纵向直流电场对流场、温度场以及烟黑生成等燃烧特性的影响进行研究。本文首先对乙烯燃烧数值研究的典型详细化学反应动力学机理模型进行对比评估,选用了合适的反应机理模型;之后建立了乙烯同轴射流扩散火焰流场、温度场、组分浓度场以及烟黑体积分数的数值计算模型;最后发展了一个同轴射流扩散火焰耦合电场计算模型的求解器,分析了外加纵向直流电场对乙烯层流同轴射流扩散火焰的影响。本文的主要内容为以下三个方面。使用数值计算方法,以着火延滞期、层流火焰传播速度、特定组分生成浓度以及层流扩散火焰温度场作为评价标准,对目前在数值仿真研究中广泛应用的4种化学反应动力学模型进行对比评估。量化计算各模型数值计算结果与实验结果的偏差。为本文后续数值建模研究工作选用了合适的反应机理模型。得到的对于4种模型数值计算精度的定量对比结果为使用详细化学反应机理模型开展的数值研究过程中的机理模型选用提供了数据参考依据。通过反应机理模型的简化以及对烟黑模型的改进,使用49种组分,640个基元反应的简化机理模型以及一个双方程的烟黑模型,建立了可以描述乙烯层流同轴射流扩散火焰速度场、温度场、组分浓度场以及烟黑体积分数的数值计算模型,并对计算结果进行了准确性验证。通过改变入口体积流量及燃料流组分构成,对比了9种工况下的计算结果,研究了烟黑浓度的影响因素。发展的烟黑计算求解器对于实现工程应用条件下火焰中烟黑生成情况的快速建模很有意义。发展了一个同轴射流扩散火焰耦合电场计算模型求解器,建立了外加纵向直流电场的乙烯同轴射流扩散火焰数值计算模型。外加电场包括正向与反向电场,通过改变电场强度,对比火焰速度场、温度场、组分浓度场结果以及烟黑体积分数的变化规律,探究电场通过离子风效应对乙烯同轴射流扩散火焰燃烧特性的影响。结果表明,外加正向直流电场会提高火焰稳定性;外加反向直流电场可以有效抑制乙烯层流同轴射流扩散火焰中的烟黑生成。更多还原

【Abstract】 Fossil fuels account for a huge share of primary energy consumption,but their combustion produces a large amount of air pollutants,of which soots can significantly affect climate change and human health.Ethylene is an important intermediate product in the combustion and thermal cracking process of macromolecular hydrocarbon fuels,and is also an important precursor of soots.Electric field-assisted combustion technology has been widely focused as an efficient means to control combustion processes.In order to deepen the understanding of the soot generation characteristics of fossil fuels and to investigate the effect of applied electric field on the combustion characteristics of diffusion flame,this paper investigates ethylene combustion and soot generation using numerical methods.This paper investigates the soot generation characteristics of laminar ethylene diffusion flames and the effect of the applied longitudinal DC electric field on the combustion characteristics such as velocity,temperature,species and soot generation using ethylene fuel as the object of study.In this paper,firstly the typical detailed chemical reaction kinetic models for the numerical study of ethylene combustion are compared and evaluated and a suitable reaction mechanism model is selected.The effect of the applied longitudinal DC field on the laminar ethylene co-flow diffusion flame is analyzed.The main contents of this paper are the following three aspects.Using numerical methods,four chemical reaction kinetic models,which are widely used in numerical studies,are compared and evaluated in terms of ignition delay time,laminar flame speed,specific speices generation concentration and laminar diffusion flame temperature field as evaluation criteria.The deviation of the numerical results of each model from the experimental results was quantified and calculated.A suitable reaction mechanism model is selected for the subsequent numerical modeling research work in this paper.The results of the quantitative comparison of the accuracy of the numerical calculations of the four models are used as a reference for the selection of the kinetic models in the numerical studies using detailed chemical reaction kinetic models.By simplifying the reaction mechanism model and improving the soot model,a simplified mechanism model with 49 species and 640 reactions and a two-equation soot model were developed to describe the velocity field,temperature field,species concentration field and soot volume fraction of laminar ethylene co-flow diffusion flame,and the accuracy of the calculation results was verified.By varying the inlet volume flow rate and fuel stream component composition,the calculation results under nine operating conditions were compared,and the influencing factors of soot concentration were studied.The developed soot calculation solver is meaningful for realizing quick modeling of soot generation in flames under engineering application conditions.A co-flow diffusion flame coupled electric field calculation model solver is developed to establish a numerical calculation model of an ethylene co-flow diffusion flame with an applied longitudinal DC electric field.The applied electric field includes forward and reverse electric fields,and the effect of electric field on the combustion characteristics of ethylene co-flow diffusion flame through ionic wind effect is investigated by comparing the results of flame velocity field,temperature field,species concentration field and the variation of soot volume fraction by changing the electric field intensity.The results show that the applied forward DC electric field will improve the flame stability;the applied reverse DC electric field can effectively suppress the soot generation in ethylene co-flow diffusion flame.更多还原