Temporal atomization of a transcritical liquid n-decane jet into oxygen

• Published in: International journal of multiphase flow 2022-08, Vol.153, p.104130, Article 104130
• Main Authors: Poblador-Ibanez, Jordi, Sirignano, William A.
• Format: Article
• Language: English
• Subjects: Atomization; Low-Mach-number compressible flow; Phase equilibrium; Supercritical pressure; Transcritical flow; Volume-of-fluid
• ISSN: 0301-9322; 1879-3533
• DOI: 10.1016/j.ijmultiphaseflow.2022.104130

The injection of liquid fuel at supercritical pressures is a relevant but overlooked topic in combustion. Typically, the role of two-phase dynamics is neglected under the assumption that the liquid will rapidly transition to a supercritical state. However, a transcritical domain exists where a sharp phase interface remains. This scenario is common in the early times of liquid fuel injection under real-engine conditions involving hydrocarbon fuels. Under such conditions, the dissolution of the oxidizer species into the liquid phase is accelerated due to local thermodynamic phase equilibrium (LTE) and vaporization or condensation can occur at multiple locations along the interface simultaneously. Fluid properties vary strongly under species and thermal mixing, with liquid and gas mixtures becoming more similar near the interface. As a result of the combination of low, varying surface-tension force and gas-like liquid viscosities, small surface instabilities develop early. The mixing process, interface thermodynamics, and early deformation of a cool liquid n-decane jet surrounded by a hotter moving gas initially composed of pure oxygen are analyzed at various ambient pressures and gas velocities. For this purpose, a two-phase, low-Mach-number flow solver for variable-density fluids is used. The interface is captured using a split Volume-of-Fluid method, generalized for the case where the liquid velocity is not divergence-free and both phases exchange mass across the interface. The importance of transcritical mixing effects over time for increasing pressures is shown. Initially, local deformation features appear that differ considerably from previous incompressible works. Then, the minimal surface-tension force is responsible for generating overlapping liquid layers in favor of the classical atomization into droplets. Thus, surface-area growth at transcritical conditions is mainly a consequence of gas-like deformations under shear rather than spray formation. Moreover, the interface can be easily perturbed in hotter regions submerged in the faster oxidizer stream under trigger events such as droplet or ligament impacts. The net mass exchange at high pressures limits the liquid-phase vaporization to small liquid structures. •Transcritical liquid injection displays different features than subcritical flows.•Phase equilibrium allows the coexistence of two fluid phases at supercritical pressures.•Surface deformation is highly affected by local mixing in both phase