Experimental study of elliptical jet from supercritical to subcritical conditions using planar laser induced fluorescence

Abstract

The study of fluid jet dynamics at supercritical conditions involves strong coupling between fluid dynamic and thermodynamic phenomena. Beyond the critical point, the liquid-vapor coexistence ceases to exist, and the fluid exists as a single phase known as supercritical fluid with its properties that are entirely different from liquids and gases. At the critical point, the liquids do not possess surface tension and latent heat of evaporation. Around the critical point, the fluid undergoes large changes in density and possesses thermodynamic anomaly like enhancement in thermal conductivity and specific heat. In the present work, the transition of the supercritical and near-critical elliptical jet into subcritical as well as supercritical environment is investigated experimentally with nitrogen and helium as the surrounding environment. Under atmospheric condition, a liquid jet injected from the elliptical orifice exhibits axis switching phenomena. As the injection temperature increases, the axis switching length also increases. Beyond the critical temperature, the axis switching is not observed. The investigation also revealed that pressure plays a major role in determining the thermodynamic transition of the elliptical jet only for the case of supercritical jet injected into subcritical chamber conditions. At larger pressures, the supercritical jet undergoes disintegration and formation of droplets in the subcritical environment is observed. However, for supercritical jet injection into supercritical environment, the gas-gas like mixing behavior is observed.

On the Fuel Spray Transition to Dense Fluid Mixing at Reciprocating Engine Conditions

“…This behavior is attributed to the absence of phase boundary between the injectant and the CVC gas. To the authors’ knowledge, this appears to be the first time that the injection of a supercritical hydrocarbon fuel has been considered experimentally, and similar dynamics have been previously observed for the injection of other fluids (e.g., injection of fluoroketone into N 2 and He) at supercritical conditions.…”

“…Such processes include those that occur when the pressure and temperature of the system exceed the critical properties of the injected liquid fuel. In contrast to conventional sprays that feature droplets, the reduced surface tension and reduced heat of vaporization may then instead promote diffusional, gas-like dynamics. − However, while this transcritical fuel injection has been extensively investigated in aerospace applications, ,− its relevance to modern, reciprocating internal combustion engines is contested.…”

Selected Results of the Collaborative Research Center “Droplet Dynamics under Extreme Ambient Conditions” SFB-TRR 75

“…Therefore, it is essential to be able to retrieve all possible states of sub-, trans-and supercritical mixtures, regardless of their (pseudo-) gaseous or (pseudo-) liquid state. In order to establish such a numerical tool which is both computationally efficient and economically acceptable, a Large Eddy Simulation (LES) framework which includes the WALE subgrid-scale model and well-adapted multi-component species diffusion helium environment as experimentally investigated in [5,6]. Exemplary, a preliminary qualitative result representing the density field is shown in Figure 3 in comparison with available experimental data [5].…”

“…In order to establish such a numerical tool which is both computationally efficient and economically acceptable, a Large Eddy Simulation (LES) framework which includes the WALE subgrid-scale model and well-adapted multi-component species diffusion helium environment as experimentally investigated in [5,6]. Exemplary, a preliminary qualitative result representing the density field is shown in Figure 3 in comparison with available experimental data [5]. Thereby, the jet penetration is well predicted while a deviation is observed in the jet spreading rate.…”

“…Figure 3. Left: Computational domain embedded in a drawing which corresponds to the experimental setup used in[5,6]; Right: Comparison of experimental[5] and preliminary simulation results of the density field.…”