Experimental study of breakup and atomization characteristics of liquid carbon dioxide jet under high-pressure environment

Considering the working conditions of a Mg/CO2 rocket engine for Mars exploration, an experimental investigation was carried out to study the breakup and atomization properties of a liquid CO2 jet in a high-pressure environment. It is shown that the pressure ratio has a significant effect on the location and process of jet evaporation, resulting in significant difference in jet morphology and breakup characteristic. Two dividing points were identified, one near the CO2 triple point and the other near the saturation point. As the pressure ratio increases, the thermodynamic driving force for jet breakup weakens, leading to larger droplet sizes. The breakup length of the free round jet and Sauter mean diameter are functions of the Weber number and Jacob number, which are influenced by vapor content, injection velocity, and gas-liquid density ratio, in the mass flowrate range of 5.9-9.1 g/(mm(2).s). A thermodynamic mechanism dominates when the ambient pressure in the atomize room is low enough, resulting in an unimodal distribution of droplet sizes. When the ambient pressure is in the range of 1-2.5 MPa, both thermodynamic and mechanical breakup mechanisms are active, resulting in a bimodal distribution of droplet sizes.