Correlation and prediction of biodiesel density for extended ranges of temperature and pressure

NIEVES M.C. TALAVERA PRIETO; ABEL M.G. FERREIRA; ANTONIO T.G. PORTUGAL; RUI J. MOREIRA; JAIME B. SANTOS

FUEL

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2015 vol. 141 p. 23 - 38

0016-2361

The knowledge of biodiesel density over large ranges of temperature and pressure is important for predicting the behavior of fuel injection and combustion systems in diesel engines, and for the optimization of such systems. In this study, cottonseed oil was transesterified into biodiesel and its density was measured at temperatures between 288 K and 358 K and pressures between 0.1 MPa and 30 MPa, with expanded uncertainty estimated as ±1.6 kg m−3. Experimental pressure-volume-temperature (pVT) cottonseed data was used along with literature data relative to other 18 biodiesels, in order to build a database used to test the correlation of density with temperarure and pressure using the Goharshadi-Morsali-Abbaspour equation of state (GMA EoS). To our knowledge, this is the first that density measurements are presented for cottonseed biodiesel under such high pressures, and the GMA EoS used to model biodiesel density. The new tested EoS allowed correlations within 0.2 kg m−3 corresponding to average relative deviations within 0.02%. From these results of correlation with the GMA EoS mechanical coefficients such as thermal expansivity, isothermal compressibility and internal pressure were calculated. In spite of their effect in power and fuel injection, those properties are rarely presented for biodiesel, especially at high pressures. As a remarkable result of this study, it was found a crossing point for the thermal expansivity, where isothermic curves cross. The built database was used to develop and test two new full predictive models valid up to 373 K and 130 MPa. One of the proposed predictive methods (4PGMA) followed from the GMA EoS, and the other (DU) was derived from the observed linear relation between density and degree of unsaturation (DU), which depended from biodiesel FAMEs profile. The average density deviation of 4PGMA was only about 2 kg m−3, and 3 kg m−3 for the DU method within the temperature and pressure limits of application. These results represent appreciable improvements in the context of density prediction at high pressure when compared with other equations of state.