超临界喷射作为一种新型燃料供给方式，可以实现快速混合气制备，并降低对供油系统的依赖，在未来先进柴油机上具有很大的应用潜力。超临界燃料由于表面张力近似为零，雾化、蒸发等现象消失，其喷射混合机理和燃烧特性与传统液体燃料完全不同，至今还没有被完全理解。本项目在高温高压定容燃烧弹和蓝宝石光学发动机上，采用可视化测试技术研究超临界射流结构形态、混合气形成与发展规律、着火燃烧放热特征，并与数值模拟相结合，系统揭示超临界燃料射流结构与传统液体燃料的差异、混合气形成与输运机制、着火和燃烧特性，并提出超临界燃烧控制方法。其研究不仅对发动机高强化燃烧条件下的超临界喷射混合机理和燃烧特性进行了有益的探索，同时对超临界流体可视化测试在发动机研究领域的实际应用具有重要参考价值。

As a novel fuel supply approach, supercritical fuel injection into a supercritical environment can achieve mixture formation rapidly, reduce the dependence on the fuel supply system and have a great applied potential to advance diesel engine technologies in the future. Because the surface tension of supercritical fluids is close to zero, the phenomena of atomization and evaporation disappear and the mechanisms of supercritical fuel injection, mixture formation and combustion are totally different from those under subcritical conditions. Supercritical fuel injection, mixing, and combustion have received little research attention and are poorly understood. In this proposal visualization techniques will be used to investigate the structure of supercritical fuel injection, mechanisms of mixture formation and development, ignition delay, and characteristics of combustion and heat release in a combustion bomb and a sapphire optical engine under supercritical high pressure and high temperature conditions. Combined with numerical simulation, the features of supercritical fuel injection and mixture formation will be revealed, as well as characteristics of ignition delay and combustion. Based on the findings of this research project, the method of controlling supercritical fuel combustion will be proposed. The proposed research is essential not only to the exploration of the theory of supercritical fuel injection, mixing and combustion under the intensified conditions, but also to the evaluation of the visualization techniques applicable to supercritical fluids in engine measurements.