Transition of diesel spray to a supercritical state under engine conditions
Transition of diesel spray to a supercritical state under engine conditions
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DOI：
10.1177/1468087415604281
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发表时间：
2016-01
影响因子：
2.5
通讯作者：
M. Wensing;T. Vogel;Gudrun Götz
中科院分区：
文献类型：
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作者：
M. Wensing;T. Vogel;Gudrun Götz
现代内燃机的过程操作条件可能超过喷射液体燃料的热力学临界点。这就提出了这样的问题：即使存在环境气体，燃料或至少其某些成分是否也会转变为超临界状态。为了更好地了解柴油发动机燃油喷射过程中的传热和传质，需要进一步研究。本文研究了超临界条件下或注入超临界条件下燃料及其成分的相行为。在简要回顾了该主题的研究现状后，我们使用状态方程对三种单组分液体（正庚烷、正十二烷、正十六烷）及其二元混合物在氮气环境中超临界条件下的相行为进行了研究。在第一个实验中，通过在高压、高温恒容室内应用与发动机相关但稳定的状态条件，这些液体与柴油燃料一起成功转变为超临界状态。没有发现环境氮气对所检测流体的相行为有影响。为了进一步研究，使用生产型柴油喷射器在瞬态喷射过程中并在典型的发动机相关时间尺度将多组分燃料喷射到燃烧室中。通过米氏散射、激光诱导荧光和阴影成像检查燃料喷雾。获得的信息证实了超临界状态和跨临界相变的存在。可以看到具有明显波动的高密度区域。理论回顾与实验结果相结合表明，现代柴油发动机在较高负荷下所存在的高压和高温条件下喷射的燃油不会蒸发，而是会过渡到相界消失的超临界状态，但不会沸腾或改变密度。
Process operating conditions of modern internal combustion engines can exceed the thermodynamic critical point of an injected liquid fuel. This raises the question of whether the fuel, or at least some of its components, transition to a supercritical state, even in the presence of an ambient gas. Further investigation is required for a better understanding of heat and mass transfer during the process of fuel injection in diesel engines. This article investigates the phase behavior of fuels and their components under supercritical conditions or when injected into such. After a brief review of the current state of research on the topic, we present our study of the phase behavior of three single-component liquids (n-heptane, n-dodecane, n-hexadecane) and their binary mixtures under supercritical conditions in a nitrogen environment using equations of state. In first experiments, these liquids along with a diesel fuel were successfully transitioned to supercritical states by applying engine-relevant but steady state conditions inside a high-pressure, high-temperature constant volume chamber. No influence of the ambient nitrogen on the phase behavior of the examined fluids was found. For further investigation, multicomponent fuels were injected into the chamber in a transient injection process and at typical engine-relevant time scales using a production-type diesel injector. The fuel sprays were examined with Mie scattering, laser-induced fluorescence, and shadowgraphic imaging. The information obtained confirms the presence of a supercritical state and a transcritical phase change. Areas of high density with pronounced fluctuations were visible. The theoretical review in combination with the results obtained from the experiments indicate that fuel injected under the high-pressure and high-temperature conditions, that are present in modern diesel engines at higher loads, does not evaporate but rather shows transition to a supercritical state with a disappearing phase border, but without boiling or changing density.