基于壁面润湿特性的内燃机燃油喷雾湿壁流固耦合过程可控性研究

The phenomenon of wall-wetting due to fuel injection has significant influence to quality of combustion and emission level of compression ignition engines; it is also one of the major reasons that leads to high HC and CO emission of the premixed compression ignition mode. In order to enhance the combustion stability and reduce the HC and CO emission, based on the latest development in the areas of both internal combustion engine and material engineering, the present research will take an inside look into the solid-fluid coupling process following the wall-wetting due to fuel injection, from a wettability point of view. The research will be carried out based on a high pressure common-rail, fixed-volume injection rig and also an optical I.C engine test rig. Technologies such as high-speed imaging, laser diagnostics, chemical kinetic analysis and thermal dynamic analysis will be used for determining the effects of the wall-wettability to the behavior of the fuel droplet upon the wall during the stage of pre-flame reaction, including such as spreading, evaporation and remixing process under different boundary conditions. The experimental results will also be used to establish a database for wettabilitis of different fuels upon various mental materials, and also a new physical model for describing the solid-fluid coupling process will be presented. Finally, controlling strategies for the above coupling process will be proposed with the wettability as the control variable. The research outcomes generated from this project will hopefully make significant contributions to the boundary control theories of internal combustion engine, and therefore improving the stability and controllability of turbulent combustion to reduce HC and CO emission of the premixed compression ignition engine.

燃油喷雾湿壁现象对发动机的燃烧及排放具有重要影响，是影响均质/预混压燃发动机燃烧边界可控性、燃烧稳定性，造成HC、CO排放高的主要原因之一。本项目结合当前内燃机及材料学领域的最新研究进展，以固体材料表面润湿性为切入点，针对湿壁燃油液滴与燃烧室壁面间的流-固耦合发展过程及其可控性开展研究工作。以高压共轨-定容喷射系统、可视化光学发动机为主要试验平台，借助高速摄影、激光诊断技术及化学动力学分析、热力学分析等手段，研究确定不同边界条件下壁面润湿性对焰前反应阶段湿壁液滴铺展、蒸发及二次混合的影响规律，建立不同金属材料与不同燃料间的润湿性评价标准及润湿性数据库，建构完善湿壁后流固耦合发展过程的物理模型。最终以壁面润湿性为控制变量，提出针对喷雾湿壁的主动控制方法及控制策略。本研究对完善极端条件下内燃机燃烧边界控制理论，提高压燃式发动机湍流燃烧的可控性、稳定性，降低HC、CO排放均具有重要意义。

本项目针对前内燃机、燃气轮机等动力机械的湍流燃烧过程控制，以提高湍流燃烧过程可控性为研究目标，以在各类动力机械中普遍存在的喷雾湿壁现象为切入点，对具有不同润湿性的燃烧室金属表面制备技术及在不同润湿性表面上燃油液滴、喷雾撞壁后的流固耦合发展过程的主动控制技术展开了研究。建立了特殊润湿性金属表面制备平台、固-液接触角分析平台、壁面蒸发过程纹影光学测试平台、定容弹喷雾及可视化光学发动机实验平台、CFD数值模拟及分子动力学仿真分析平台。基于上述研究平台开展并完成了对目标金属壁面的制备方法和不同壁面条件下撞壁燃油液滴及喷雾流固耦合发展过程的试验研究。阐明了燃料理化特性、壁面润湿性、喷油特征参数及实验边界条件对燃油单液滴及喷雾撞壁后形态发展和蒸发过程的影响规律及作用机理。建立了具有不同微观形貌的金属壁面润湿特性参数数据库，构建了基于流体力学和分子动力学的燃油液滴及喷雾撞击具有不同微观形貌壁面及撞壁后流固耦合发展过程的数学模型。在实验及数值模拟的研究结论的基础上，根据发动机缸内热氛围场分布规律，制定了基于燃烧室不同热氛围区域的壁面润湿性控制策略即燃油喷雾湿壁主动控制策略，实验验证了所提出的控制策略在冷起动等特殊工况下对减少近壁区池火燃烧比例和降低HC、CO排放等方面的效果。本项目的研究成果对于细化现有的发动机喷雾模型、完善高温高压条件下撞壁及湿壁相关的流-固耦合计算方法、提高极端条件下低温燃烧模式对湍流燃烧过程的控制精度、降低发动机不完全燃烧产物和提高发动机燃烧效率均具有重要的理论指导意义。至项目截至日期，共计发表学术论文18篇。其中国内外重要期刊文献10篇， SCI检索收录5篇，EI检索收录10篇。国内外重要会议论文9篇， CPCI检索收录2篇；提交中国专利申请18件，授权14件，尚在实质审查的4件；提交软件著作权申请12项，全部授权；获吉林省自然科学学术成果二等奖1项。