Estimation of thermophysical properties of a hydrocarbon fuel at supercritical pressure

Abstract

A good understanding of the thermophysical properties of hydrocarbon fuels at supercritical pressure is important to evaluate the performance and optimize the structure of propulsion systems of hypersonic vehicles. In-situ experimental measurements are difficult to conduct directly because of the extremely high pressure and high temperature. In this study, a novel general framework of inverse estimation is established to determine the nonlinear temperature-dependent thermophysical properties, e.g., density, thermal conductivity, viscosity, and specific heat, of hydrocarbon fuels at supercritical pressures. The steady conservation equations of mass, momentum, and energy are completely solved in the forward model. The complex-variable-differentiation method, which is applied to accurately calculate the sensitivity coefficient matrix in inverse analysis, is successfully incorporated into an in-house complex variable finite volume code. The versatility of the current method is verified and the effect of a number of key influential parameters, including initial value, relaxation factor, function form, and measurement error on the inverse results at a supercritical pressure of 5 MPa are investigated in detail. Inverse estimations take less than 30 iterations to achieve convergences with a global residual of less than 10−5. The accuracy and robustness of inverse estimations of single and multiple thermophysical properties are examined. The present work offers an efficient tool to predict different temperature dependencies of the thermophysical properties of hydrocarbon fuels over a wide range of temperature. It will be beneficial to the structural design of hypersonic vehicles.