Abstract
The molecular compressibility, which is a macroscopic quantity to reveal the microcompressibility by additivity of molecular constitutions, is considered as a fixed value for specific organic liquids. In this study, we introduced two calculated expressions of molecular adiabatic compressibility to demonstrate its pressure and temperature dependency. The first one was developed from Wada’s constant expression based on experimental data of density and sound velocity. Secondly, by introducing the 2D fitting expressions and their partial derivative of pressure and temperature, molecular compressibility dependency was analyzed further, and a 3D fitting expression was obtained from the calculated data of the first one. The third was derived with introducing the pressure and temperature correction factors based on analogy to Lennard-Jones potential function and energy equipartition theorem. In wide range of temperatures(293<T/K<393)and pressures(0.1<P/MPa<210), which represent the typical values used in dynamic injection process for diesel engines, the calculated results consistency of three formulas demonstrated their effectiveness with the maximum 0.5384% OARD; meanwhile, the dependency on pressure and temperature of molecular compressibility was certified.
Highlights
In modern diesel engine, the injection pressure of fuel spray system continuously was elevated to achieve better atomization, combustion, and emission effect and even reach 200 MPa or more, which increase vastly the dynamics sensibility of fuel compressibility
This study showed that the molecular compressibility is related to molecular specific structure, and the negative temperature correction coefficient in (5) presented temperature dependence of molecular compressibility: nG
Based on [15] data that sound velocity was obtained from experimental and density was obtained from calculated value by (7), km was calculated in 0.1 to 210 MPa and 303.15 to 383.15 K and the fitting results were presented with isothermal characteristics for methyl caprate and ethyl caprate in Figures 1 and 2
Summary
The injection pressure of fuel spray system continuously was elevated to achieve better atomization, combustion, and emission effect and even reach 200 MPa or more, which increase vastly the dynamics sensibility of fuel compressibility. In order to clarify the connection between the microscopic chemical structure of organic liquids and the compressibility from investigation of sound velocity and density, many theoretical analyses and derivations have been performed to determine these properties. Later Daridon et al [12] divided the FA esters molecule into five bigger functional groups to contribute to the molecular compressibility; molecular compressibility was demonstrated with slight temperature dependency These investigations provide a quantitative connection between macroproperties and molecular microstructure, but the literature on the compressibility for FA esters and biodiesels is still very scant relative to its species; most data are available only at atmospheric pressure and in a narrow range of temperature and could not match the fuel working conditions in injection system. The consistency of calculated results derived from different principles verified effectiveness of these formulas and confirmed the dependency of molecular compressibility on pressure and temperature
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