预混醇醚氛围下生物柴油扩散火焰的试验和理论研究

The advantages of lower NOx and PM emissions for diffusion combustion in reactivity charge have been identified by RCCI (reactivity charge compression ignition) engine tests. However, the shortage in understanding premixing diffusion flames in reactivity charge has resulted in the failing in developing some theoretical criteria for diffusion combustion in reactivity charge, to realize combustion controlling. Its combustion controlling is still on the basis of experience summarization. This project plans to study the reaction performances of bio-diesel diffusion flames in premixed methanol or dimethyl ether（DME）charge in air, by means of experimental measurements, theoretical calculations and flame simulations. On the basis of flame measurements, the effects of reactivity charge on the structure of premixing diffusion flames are to be explored, in order to find the stabilization mechanism of jet flame in reactivity charge and understand the combustion characteristics of premixing diffusion flames. On the basis of flame simulations, the formation and consumption of some key radicals and some active species in flames will be traced, to find the interplaying channels between premixed reaction zone and diffusion one. The promoting mechanism of reactivity charge on combustion can be found. The influences of premixed reactivity charge on hazardous pollutions are to be studied, and an investigation will be implemented to explore the synergistic effects between bio-diesel and alcohol ether fuels, to find the methods to simultaneously suppress the formation of hazardous pollutions. Finally, the adaptive characters are assessed for the studied fuels on diffusion combustion in reactivity charge and maps of optimum zone for premixing diffusion combustion should be achieved in terms of the ratio of premixing fuel/ jet fuel, the temperature of reactivity charge, EGR ratio and so on. This project is not only a theoretical study in combustion, but also a fundamental study on alternative fuels, the predicted results of which can enrich combustion theory and be useful for promoting applications of alternative fuels as well.

活性氛围扩散燃烧低NOx和PM优点已在活性氛围压燃（RCCI）发动机上得到验证。但由于迄今仍未理解活性氛围扩散燃烧实质，使得如RCCI等的活性氛围燃烧调控尚未有理论准则，仍基于经验总结。本项目采用试验测试、理论计算和数值模拟相结合的方法，探寻预混甲醇、二甲醚氛围下生物柴油扩散火焰的反应行为。基于火焰测试，剖析氛围对预混扩散火焰结构的影响，发现活性氛围射流火焰形成机制，明晰燃烧规律；基于火焰计算，跟踪关键基团和活性物种的生成和消耗历程，探明预混反应区与扩散反应区的相互作用通道，揭示活性氛围促进燃烧的机理；研究氛围对有害生成的影响，发掘燃料协同效应，研究有害排放共同抑制的方法；基于多因素耦合，评估燃料组合对活性氛围燃烧的适应特性，建立以燃油比例、氛围温度、EGR率等表示的活性氛围扩散燃烧优化MAP。本项目既是燃烧理论探索，也是替代燃料的基础研究，研究成果将丰富燃烧理论，也有助于替代燃料推广。

活性氛围扩散燃烧具有低NOx和PM的优点，已在活性氛围压燃（RCCI）发动机上得到应用验证。为进一步明晰活性氛围扩散燃烧本质，本项目基于火焰测试计算，开展了相关基础研究。研究了活性氛围加持下的复合火焰结构转换、燃烧放热，NO以及碳烟前驱体，苯（A1）生成等特性，总结了活性预混氛围对扩散火焰燃烧反应动力学的影响途径。不同预混方案对火焰结构有明显影响，甲醇预混火焰排放因子随当量比增加而显著降低，而二甲醚预混火焰随当量比增大呈温和的增加, N2的浓度和火焰温度的竞争关系在两种火焰中呈不同效应。火焰中甲醛及soot的溢出是低温生成和高温转化的共同作用结构，该效应极大地受有害物质低温浓度峰值的影响。提出了基于活性基产生/消耗率的双火焰反应区判别方法，从放热权重比角度定义了双火焰的融合、分离发展。双火焰间的热影响主要体现为火焰互为支撑，预混火焰为扩散火焰提供热环境，使得稀释燃烧得以实现，而扩散火焰显著扩展了预混燃气的稀燃极限。由于多重火焰的混杂结构的影响，更宽的火焰厚度以及更显著的活性基生成。热裂解和脱氢是生物柴油射流最主要的氧化路径，空气侧燃料预混引发火焰高温而产生的热影响会增大反应区物质的径向泄露。火焰的非预混区是A1反应最活跃区域，但并不对应于A1最大峰值浓度。空气侧燃料预混能通过调控丙炔和苯基化学反应路径影响苯形成。氢气的化学反应性对燃烧系统的作用可以总结为两方面，一是快速释热，二是通过参加基元反应，促进活性基团的生成。对于预混火焰，氢气掺混的影响主要通过基元反应效应来体现，但当氢气掺混量大到一定程度，氢气快速的热焓释放作用开始明显。在扩散火焰中，氢气输运会显著影响火焰内氢气守恒，氢气的强化输运会增强氢气的反应强度，会导致NO生成强度的增加。项目目前已发表论文8篇，其中，国际期刊6篇，SCI收录6篇，中文核心期刊1篇，国内燃烧学会议论文1篇。培养硕士研究生8名，后续成果仍在总结中。