柴油机高压喷射喷嘴内空化热力瞬态特性与空蚀机理

The high-efficiency and low-emission internal combustion engine has a high requirement for the fuel injection system with the higher injection pressure, more precise control of injection, more reliable design of system, then cavitation and erosion in injector nozzles have been one of key problems. During the previous many research about the cavitating flow characteristics in Diesel injector nozzles and the mechanisms of that cavitation promoting fuel atomization, it has been also realized that erosion damage induced by cavitation may also be associated with spray instabilities, hole-to-hole and cycle-to-cycle variations leading to degradation in the performance and even structural damage to the injector. Thus, this project is aimed at the cavitation erosion problem induced by the thermal and instantaneous high-speed cavitating flow in the multi-micro-sized-hole nozzles under CR high injection pressure. The Micro-PIV technique will be used for getting the 2d flow velocity in nozzle holes, in which the refractive index matching (RIM) technique will be introduced for resolution of the problem that a laser light sheet or beam entering the model will be refracted by the internal geometry and the blacklighting from spark-flash equipment in nanoseconds supplied to Micro-PIV system will help solve the problem caused by scattering at the surface of cavitation voids. In the constant-volume spray vessel with CR fuel injection system, the visual experimental data from the instantaneous cavitating flow in Diesel micro-channel flow orifices will be coupled with the cavitation erosion experimental data from a micro-nozzle tip made of material of AlMg5 assembled to the CR injector to acquire the quantified relationship between cavitation number, Reynolds number and cavitation erosion rate. Accordingly the cavitation erosion characteristics and mechanisms will be revealed. Based on above experimental data, the thermal cavitation model and cavitation erosion model will be setup for application to high-temperature fuel. This research will contribute to realize a more precise control of fuel injection process and a more reliable design of injection system and meanwhile will push the development of cavitation two-phase flow and cavitation erosion theory.

新一代高效低排放柴油机对燃油喷射系统提出了更高喷油压力、更精确喷油控制及更为可靠系统设计的高要求，喷嘴内空化及空蚀现象成为关键之一。前期对空化雾化机理的大量研究认识到空化的发生乃至空蚀对喷雾不稳定性、不对称性及循环变动的影响不容忽视。本项目针对高压下高温燃油多孔喷嘴微米级喷孔内高速空化瞬态流诱发的空蚀问题，研制耐高温高压的原型透明喷嘴，解决Micro-PIV测试中激光折射及强散射问题，获取喷嘴内热力作用下的空化瞬态流动信息，阐明不同结构热力空化发生机制；同时开展铝镁合金材料喷嘴快速空蚀试验，获取喷嘴空蚀形貌，两者结合获得热力作用下的空化结构、空化数、雷诺数与空蚀率间定量关系，揭示热力空蚀机理；基于实验建立适用于高温燃油的新型热力空化及空蚀模型。本项目在极限工况下对瞬态空化及空蚀机理的探索，对燃油喷射的精细控制及系统的可靠性具有重要应用价值，也必将推动空化两相流及空蚀理论的发展。

新一代高效低排放柴油机对燃油喷射系统提出了更高喷油压力、更精确喷油控制及更为可靠系统设计的高要求，喷嘴内空化及空蚀现象成为关键。本项目针对高压下高温燃油多孔喷嘴微米级喷孔内高速空化瞬态流诱发的空蚀问题，研制耐高温高压的0.1mm尺寸级别的透明喷嘴，解决Micro-PIV测试中激光折射及强散射问题，获取喷嘴内空化强瞬态流动信息，采用纳秒级高频背景光冻结捕获微小尺寸喷孔内超高速、强瞬态工况下的高清晰涡线空化现象和气泡倒吸现象，发展新型的VLES超大涡湍流数值计算模型，试验结合高性能数值模拟阐明了旋涡流场结构与涡线空化特性间关系，几何诱导片状空化、涡线空化、云空化脱落等不同形态空化发生机制及相互影响机理，并进一步揭示了粘性因素（几何结构、喷射压力、针阀运动）、介质因素（含气量、燃油温度影响下燃油物理属性、混合燃油物理属性）及物面因素（粗糙度）对喷嘴内不同形态空化流动的影响特性。同时开展铝镁合金材料喷嘴快速空蚀试验，获取喷嘴空蚀形貌，结合喷嘴内不同形态空化瞬态流动特性，获得空化结构、空化数、雷诺数与空蚀率间关系，揭示了空蚀机理；实验结合模拟建立了适用于高温高压燃油的新型热力空化及空蚀预测模型。本项目的研究工作发表SCI检索论文25篇，授权国家发明专利8项；培养的研究生获江苏省优秀博士论文1篇，校优秀硕士论文1篇；受邀在包括喷雾领域最为权威的ILASS-Asia在内的国际、国内学术会议上做邀请报告近10次，担任会议主席，承办2020ILASS-Asia国际会议1次；研究成果获江苏省科技进步二等奖1项、中国商业联合会科学技术一等奖1项、中国产学研合作创新成果优秀奖1项。本项目研究除了推动了空化两相流及空蚀理论的发展以外，对柴油机高压共轨式燃油喷射精细控制及系统的可靠性等我国“卡脖子”关键核心技术攻关具有重要的应用价值，同时对汽油机喷嘴、航空发动机喷嘴、各类燃烧器燃油喷嘴、发动机后处理尿素喷嘴等的设计研发及对其他领域空化现象的研究均具有较强的理论指导意义。