The common rail injection system with higher injection pressure can improve injection characteristics. However, relevant researches for injection characteristics under ultra-high pressures are insufficient. In this article, the results of experiments with a maximum injection pressure of 390 MPa for nine different injectors of four types are presented. The experiment showed the existence of supercritical pressure during injection. At pressures below the supercritical pressure, the injection quantity increases with increasing injection pressure, however, when the injection pressure is over supercritical pressure, the injection quantity does not increase. According to the experiment results, the supercritical injection pressure is about 300 ∼ 350 MPa. Under ultra-high pressures, fuel is strongly heated and the local sound velocity decreases, and the adiabatic flow velocity reaches the sound velocity. Under supercritical pressure, the injection rate ceases to increase and even begins to fall. The traditional equations for calculating the injection rate cannot correctly describe the injection under ultrahigh pressures. A new mathematic model with considering the fuel heating for describing the injection quantity of compressible fluid was developed, this model is not only suitable for calculating the injection quantity under ultra-high pressures, but under traditional injection pressures.

中文翻译：

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共轨系统中超高压下的燃油喷射率极限

具有更高喷射压力的共轨喷射系统可以改善喷射特性。但是，有关超高压下注射特性的相关研究还不够。本文介绍了针对四种类型的九种不同喷油嘴的最大喷油压力为390 MPa的实验结果。实验表明注射过程中存在超临界压力。在低于超临界压力的压力下，喷射量随喷射压力的增加而增加，但是，当喷射压力超过超临界压力时，喷射量不会增加。根据实验结果，超临界注入压力约为300〜350 MPa。在超高压下，燃料被强烈加热，局部声速降低，绝热流速达到声速。在超临界压力下，注射速率停止增加，甚至开始下降。用于计算喷射速率的传统方程式无法正确描述超高压下的喷射。建立了一种考虑燃料加热来描述可压缩流体喷射量的新数学模型，该模型不仅适用于计算超高压下的喷射量，而且适用于传统喷射压力下的喷射量。