Speed of sound, density and compressibility of a fuel from ultrasonic measurement under pressure

E. Ndiaye1, J. Daridon1 and D. Nasri1

1Université de Pau - LFC-R, France

Keywords: biodiesel
property: speed of sound, density, compressibility
material: petrolum fluid

Within the politic changes for the reduction of greenhouse gas emissions, biofuels present an interesting potential due to their often very well CO2 balance sheet. Numerous projects were engaged in Europe, for the development of new fuels and for the design automobile engines adapted to these carburants.

The conception of new engine requires specific systems of injection which must be perfectly designed, with this aim in mind thermophysical properties such as density and compressibility must be know with accuracy. The French project "NADIA-BIO" goes into this industrial issue. Its objectives consist in a better control of the injection (wave distribution in the High Pressure line, during the automobile inflammation and combustion process) and the impact of biodiesels (EMAG and synthetic materials) on the environment through fine numerical and experimental analyses.

The direct measurement of the coefficients of compressibility often present difficulties under pressure. It is therefore easier to determine it indirectly from the velocity of sound which can be measured in a simple and direct way with a good accuracy.

In this paper, which consist in a first study to characterization of compresibilities of fuels and biofuels, measurements of ultrasound speed were performed on model fluid (Normafluid) in the high pressure range 0.1 - 250 MPa and in the temperature range 263K - 423K. Knowing the density and the calorific capacity at 0.1 MPa, the measurement of the speed of sound have been allowed by integration of data to deduce the volumetric properties as well as its derivatives (isentropic and isothermal compressibilities as well as isobaric expansion) under the same domain of pressure and temperature.

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