Experimental study on the phase inhomogeneity and separability in supercritical state of acetone fuel

Abstract

Sufficient understanding of the supercritical state is important for exploring supercritical jet spray in thermodynamic cycle power machinery. However, in conventional studies, the phase division of supercritical state and supercritical jet spray is simple and rough, and whether the pseudo-boiling (or widom) line exists widely in various fluids, especially fossil fuels, is still not proved by experiments. In this paper, the phase inhomogeneity and separability in the supercritical state of fossil fuels are studied by using high-speed Mie scattering and UV-LAS (ultraviolet–visible laser absorption/scattering) optical diagnostic techniques. Acetone is selected as the single representative component of fossil fuels. The results show that acetone is inhomogeneous in the supercritical state at fuel temperature Tf<1.13Tc and fuel pressure Pf<1.74Pc, where Tc and Pc are the critical temperature and pressure, and can be further divided into liquid-like phase and gas-like phase, which is similar to the properties of inert fluids and simple fluids reported in previous literatures. The transition region (measured at interval of pressure 0.2 MPa) between the liquid-like phase and gas-like phase contains thermodynamic extremum lines such as constant pressure specific heat, volume expansion coefficient, and isothermal compression rate, which supports the view that the widom (or pseudo-boiling) line is used as the crossover in the supercritical state. When the state of acetone spray passes through the transition region, the liquid-like and gas-like phases will have dramatic changes in the optical and macroscopic properties of spray (For example, when the injection temperature is equal to the critical temperature of 235 °C, the stable liquid-like areas crossing the pseudo-boiling line decreases by 9 times as much as that without crossing the pseudo-boiling line). The results of this paper have important reference values for the study of the supercritical spray atomization regime and the establishment of the simulation model.