(245d) High-Pressure, High-Temperature Interfacial Tension of n-Alkane + Nitrogen Mixtures

Fuel-air interfacial tension (IFT) data, at high-pressure, high-temperature (HPHT) conditions, are fundamental data needed to design injector nozzles and improve combustion chamber performance for diesel engines as dictated by government regulating commissions. Original Equipment Manufacturers (OEM) have found that diesel fuel economy can be enhanced and emissions reduced by shrinking injector nozzle sizes to improve spray performance. However, to counteract the reduction in mass flow rate inherent with this approach, OEMs propose increasing fuel injection pressures to as high as 450 MPa. Hence, the rational design of fuel injector nozzles leading to improved combustion efficiency requires knowledge of the IFT of fuel, a complex mixture that typically contains hundreds of components, in contact with air at extreme operating conditions. To begin developing the needed database to test modern methods for predicting IFT at extreme operating conditions, we describe a HPHT, pendant-drop, tensiometer built in our lab and we demonstrate the utility of this apparatus by measuring the IFT for several different normal alkanes in nitrogen to 100 MPa and 250°C. The data obtained with this apparatus compare to within ± 3% of available literature data. The new IFT data obtained here are correlated using a corresponding states approach relating the molecular weight, density, and viscosity. The IFT data are also modeled using the Perturbed-Chain, Statistical Associating Fluid Theory in conjunction with Density Gradient Theory. The results of these model calculations are presented in this talk. Further studies are in progress with more complex, fuel-nitrogen mixtures.