Simulation of supercritical fuel injection with condensation

Abstract

Supercritical injection and the accompanying potential condensation processes were numerically investigated with a consistent treatment for both the fluid dynamics and thermodynamics with a realistic equation of state model. Qualitative and quantitative improvement was seen on the predicted injectant density with real gas simulations when compared to available experimental data, emphasizing the importance of thermodynamic property non-ideality at supercritical conditions. Recently developed phase stability and equilibrium solvers utilizing fundamental thermodynamics principles were also applied to capture phase transitions. To our knowledge, this is the first comprehensive simulation against experimental data of supercritical injection with phase separation. Furthermore, the simulation results were found to agree with the experimental results in three aspects related to the phase change. The first observation is that condensation is predicted to occur if and only if the temperature difference between the injectant and ambient is large enough to promote strong heat transfer interactions. The simulations also show that condensation becomes intensified when the chamber temperature is further reduced. Second, such condensation is only possible for supercritical-to-subcritical but not for supercritical-to-supercritical injections. Third, a condensed liquid phase is found to form at the jet boundary where the energy and mixing interactions between the-hot‖ injectant and the-cold‖ surrounding gas are strong. The intensive local heat exchange finally sends the mixture into the two-phase region by crossing the dew point line with condensation.

Phase separation analysis in supercritical injection using large-eddy-simulation and vapor-liquid-equilibrium

“…The procedures for VLE and CP calculations were successfully applied to noble gas mixtures in our previous studies. 5 Similar techniques were used by Qiu and Reitz 15,54,55 for the analysis of inert hydrocarbon injection. In this study, these procedures will be performed to study phase separation behavior for cases representative for injection in Diesel, rocket, and jet engines.…”

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

“…According to Qiu and Reitz, 21 the entrainment of the ambient gas into the injectant fluid is identified as one of the reasons for condensation behavior. The fluoroketone possesses the characteristics similar to n-dodecane used in their study 21 and the conditions meant to be supercritical for fluoroketone may not be supercritical for either fluoroketone-N 2 system or fluoroketone-He system. Moreover, the mixing is first encountered in the interfacial region alone and the bulk supercritical fluid, without losing the enthalpy maintains the supercritical state.…”

“…The computational study of super-to supercritical and super-to subcritical was done by Qiu and Reitz. 21 The experimental and injection conditions chosen for the simulation is similar to those investigated by Roy et al 16 Their computational results were compared against the experimental results of Roy et al, 16 and the core length of the simulated jet agreed with the experiment.…”

An investigation of thermodynamic states during high-pressure fuel injection using equilibrium thermodynamics

“…However, the equilibrium state must have the minimum Gibbs free energy, and a single-phase solution may not be able to satisfy this requirement. Thus, extra phases may need to be introduced to lower the Gibbs free energy [24][25][26][27]. Due to the small sizes of drops in high pressure fuel injection, spray models are generally subgrid-scale formulations, which assume that single, isolated drop correlations can be used to model vaporization and condensation processes.…”

“…In contrast, the density gradient across the shear mixing layer is found to Body Page 5 of 30 Body reduce significantly as surface tension effects are suppressed, and "finger-like" structures instead of droplets are observed in experiments [30][31][32][33][34]. Planar laser induced fluorescence has been used to investigate supercritical injection and mixing with the formation of another liquid phase [35] and such experiments have been modeled by Qiu and Reitz [25]. A number of works focus on modeling supercritical flows and fuel evaporation processes under transcritical conditions [36][37][38][39][40][41][42][43][44].…”