Abstract In order to reduce negative influence of fossil fuels on environment, use of various renewable resources is highly promoted. Terpenes, naturally occurring in plants, can be added to petroleum fuel as its substitute up to a certain share. Thermodynamic properties of a fuel under high pressure and moderate temperature conditions are of significant importance for engine efficiency. This work reports density measurements of pure p-cymene, α-pinene, limonene and citral at temperatures (293.15–413.15) K and pressures (0.1–60) MPa, applying an Anton Paar DMA HP measuring cell. Density data were fitted by modified Tammann-Tait equation where the absolute average percentage deviation between measured and calculated densities was about 0.010%. The obtained parameters were used to estimate the isothermal compressibility, the isobaric thermal expansion coefficient, the internal pressure, and the difference between specific heat capacity at constant pressure and at constant volume. For examined compounds, all thermodynamic properties, except the internal pressure, decrease with pressure rise along an isotherm and increase as temperature increases at a constant pressure. The intersection point of isotherms for the isobaric thermal expansion coefficient for pure citral was registered at pressure 47 MPa, while for other analyzed terpenes the intersection point is above 60 MPa, outside the measurements pressure range.

中文翻译：

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高压条件下纯对伞花烃、α-蒎烯、柠檬烯和柠檬醛的实验密度和衍生热力学性质

摘要 为了减少化石燃料对环境的负面影响，各种可再生资源的利用得到大力推广。萜烯，天然存在于植物中，可以添加到石油燃料中作为其替代品，达到一定比例。燃料在高压和中等温度条件下的热力学特性对发动机效率非常重要。这项工作报告了使用安东帕 DMA HP 测量池在温度 (293.15–413.15) K 和压力 (0.1–60) MPa 下对纯对伞花烃、α-蒎烯、柠檬烯和柠檬醛进行的密度测量。密度数据通过修正的 Tammann-Tait 方程拟合，其中测量密度和计算密度之间的绝对平均百分比偏差约为 0.010%。获得的参数用于估计等温压缩性，等压热膨胀系数、内部压力以及恒压和恒容下的比热容之差。对于受试化合物，除内部压力外，所有热力学性质均随压力沿等温线升高而降低，并在恒定压力下随着温度升高而升高。纯柠檬醛等压热膨胀系数的等温线交点在 47 MPa 压力下记录，而对于其他分析的萜烯，交点高于 60 MPa，超出测量压力范围。沿等温线随压力升高而降低，在恒定压力下随温度升高而升高。纯柠檬醛等压热膨胀系数的等温线交点在 47 MPa 压力下记录，而对于其他分析的萜烯，交点高于 60 MPa，超出测量压力范围。沿等温线随压力升高而降低，在恒定压力下随温度升高而升高。纯柠檬醛等压热膨胀系数的等温线交点在 47 MPa 压力下记录，而对于其他分析的萜烯，交点高于 60 MPa，超出测量压力范围。