How do fuel and air mix, if a liquid fuel is injected into an environment featuring pressure and temperature that exceed the critical pressure and the critical temperature of the fuel? It is subject of current discussion on whether and if so when, the fuel/air-mixture becomes supercritical or not. We here report experimental data comprising three mixture properties that are relevant for the current debate, all spatially and temporally resolved throughout the spray and injection event: The overall composition of the fuel/air-mixture, the liquid fraction of the fuel/air-mixture, and the temperature of the liquid phase. To this end, we applied Raman spectroscopy and gave special attention to the signature of the Raman OH-band of ethanol, which we used as fuel. Its signature is connected to the development of a hydrogen bonded network between the ethanol molecules and thus extremely sensitive to thermodynamic state and temperature. Measurements were carried out in a high-pressure, high-temperature combustion vessel in a pressure range of 3−8 MPa and a temperature range of 573−923 K. For the highest set temperature we found ethanol in liquid-like mixtures that exceeded the mixture critical temperature. This is an indication of the existence of a single-phase mixing path.

如果将液体燃料注入压力和温度超过燃料的临界压力和临界温度的环境中，则燃料和空气如何混合？当前讨论的主题是燃料/空气混合物是否以及何时变得超临界。我们在此报告的实验数据包括与当前辩论相关的三种混合物特性，它们在整个喷雾和喷射过程中在空间和时间上均得到解决：燃料/空气混合物的整体组成，燃料/空气混合物的液体比例，以及液相温度。为此，我们应用了拉曼光谱，并特别注意了用作燃料的乙醇的拉曼OH谱带的特征。它的特征与乙醇分子之间氢键网络的发展有关，因此对热力学状态和温度极为敏感。在高压，高温燃烧容器中进行测量，压力范围为3-8 MPa，温度范围为573-923K。对于最高设定温度，我们发现液体状混合物中的乙醇超过了混合物临界温度。这表明存在单相混合路径。对于最高设定温度，我们发现液体状混合物中的乙醇超过了混合物的临界温度。这表明存在单相混合路径。对于最高设定温度，我们发现液体状混合物中的乙醇超过了混合物的临界温度。这表明存在单相混合路径。