Investigation of fluid properties at non-ambient conditions
A requirement for thermophysical property data of diesel fuels at conditions removed from ambient was identified. A series of measurements of the pressure-volume-temperature relations of diesel fuels was undertaken using a Micro-PVT apparatus at pressures to 300MPa in the temperature range 25 to 75°C. A new calibration procedure for this instrument was devised to enable measurements of high accuracy to be made. Viscosity measurements of diesel fuels over a range of temperature and pressure were made using the National Engineering Laboratory high pressure viscometer to pressures of 460MPa in the temperature range 25 to 100°C.Corresponding states theory was applied for compressed liquid density prediction. Improvement in density prediction in this region was found through use of iso-octane and heptadecane as reference fluids. Compressibility factors of these were represented by Tait-style equations. An iterative solution technique was developed to allow the corresponding states method to be applied to diesel fuelsusing limited density measurement and a guess value of boiling point as inputs. Densities predicted from this method agreed well with measurements made using the Micro-PVT apparatus. Hard sphere theory was applied as a method for viscosity prediction. Despite the complexity of the diesel fuel mixture, reasonable estimates of viscosity were made with limited measurement input at higher temperatures. At lower temperatures, an additional simple empirical correction term was required. A method of viscosity estimation of complex hydrocarbon mixtures based upon composition is presented. Further development of this would require additional measurements and greater characterisation of the fuel.