高功率密度汽油机换气过程优化及其对发动机性能影响机理的研究

The project is focus on the problem of the high power-density gasoline engine, including knock, super-knock and low speed torque. The auto-igntion mechanism of the origins induced super-knock and optimization of gas exchange process is the most important attention of this project. The following contents must be fulfilled. .(1) The effect of its compostion, fuel dilution and external conditions (temperature, pressure and air-fuel ratio) on auto-ignition of the origins induced super-knock are studied in a constant volume combustion bomb. The condition required for auto-ignition of the origins are indentified and the auto-igniton mechanism is developed..(2) The detailed experimental studies on scavenging effect of high power-density gasoline engine are conducted through a unique optical arrangement. The mechanism of suppressing super-knock with scavenging effect are proposed and the control method of scavenging process are developed to improve its efficiency..(3) The effect of gas exchange process on combustion and emission characteristics of high power-density gasoline engine are explored. To explore the effect of gas exchange process on air charge and residual gas fraction, detailed experimental investigation are conducted in testing bench and a model is proposed to estimate the air charge and residual gas fraction. Detailed experimental investigations are conducted in testing bench to study the effcet of gas exchange process on the performance of three-way catalyst and turbocharger..When the three parts are accomplished, a control strategy of gas exchange process must be developed for high power-density gasoline engine to realize a much higher efficient and cleaner combustion..This project is an innovative work with higher academic value, and it will promote the development of combustion theory and emission control of gasoline engine. The success of this project can greatly decrease the fuel consumption of gasoline engine, and it is helpful to decrease automotive exhaust emission, ensure global energy security.

高功率密度汽油机极具节能减排潜力，但也存在容易发生爆震、超级爆震和低速扭矩不足等缺陷。.项目以高功率密度汽油机为研究对象，重点探索超级爆震诱发源的自燃机理和换气过程对汽油机性能的影响。利用定容燃烧弹，分析研究超级爆震诱发源的自燃条件，获得其自燃机理；利用光学发动机研究换气过程高效扫气的组织机制，明确扫气抑制超级爆震机理；研究换气过程对汽油机燃烧过程和排放特性的影响，建立耦合换气过程的新鲜充量和残余废气预测模型，明确换气过程优化控制策略。.项目的研究工作极具创新性和学术价值，有望在汽油机燃烧理论和排放控制技术等方面取得新进展。项目的成功实施对降低汽油机油耗水平，减少汽车排气污染具有重要作用，对保障我国能源安全具有重大战略意义。

项目以高功率密度汽油机为研究对象，探究超级爆震诱发源的自燃机理以及换气过程对汽油机性能的影响，以进一步提高汽油机的功率密度和热效率。主要研究结论有：.（1）高效扫气过程可以抑制超级爆震并提升汽油机动力性。气门重叠角大且时刻越早有利于高效扫气；通过燃烧室结构和进排气正时的优化，扫气效率和颗粒物清除率能达到99.5%和61.7%，显著降低超级爆震发生几率。进气门开启正时对扫气和燃烧的影响大。采用非同步排气门正时，湍流动能呈现“三峰”变化，缸内平均流速增加，燃油蒸发速度快，混合气更加均匀。非同步进气门正时对缸内残余废气影响不大，燃烧速率变小。.（2）润滑油膜的蒸发过程分为缓慢蒸发、急速蒸发和蒸发凝胶等阶段。在稳定蒸发期间，油膜的质量损失速率不变，与油膜表面接收到的净热流密度、油膜厚度呈正比关系，与试验板的导热系数呈反比关系。润滑油/汽油混合油膜的蒸发过程分为瞬态加热、平衡蒸发和蒸发凝胶等阶段。初始阶段的混合油膜质量损失速率与掺混比呈正比关系，平衡蒸发阶段的质量损失速率随着掺混汽油比的增加而降低。.（3）建立了缸内新鲜空气量、气门重叠期间的新鲜充量、扫气量或废气回流量、残余废气的数学模型，可对耦合换气过程的缸内新鲜充量和残余废气进行预测；基于催化器前热量损失、催化器中热量损失及氧化还原反应放热等数学模型对三效催化器温度进行预测。.（4）润滑油液滴蒸发历程分为初始加热、快速蒸发和缓慢蒸发等阶段，润滑油/汽油混合液滴以波动蒸发为主。润滑油液滴的蒸发过程较为稳定，混合液滴的蒸发过程则伴随着气泡生成、液滴变形、液滴破碎和不完全微爆等剧烈现象。液滴着火过程可大致分为滞燃期/初始蒸发阶段、燃烧期和熄灭期。随着混合液滴中汽油比例的增大，液滴的着火延迟时间逐渐减小。当环境温度升高的时候，液滴点火延迟减小。液滴蒸发和燃烧残余物会在气缸内形成炽热点，成为汽油机超级爆震的诱发源。