Prospects of UDMH Organic Gel Droplet Evaporation and Combustion Model

Abstract

The organic gel propellants have the advantages of both solid and liquid propellant, but the catching fire and burning process of organic gel droplet appears obvious vapor ejection and flame disturbance. This unsteady combustion phenomenon of organic gel droplet is different from the quasi-steady combustion of conventional liquid droplet and produces great influence on the spray combustion flow field of gel liquid rocket engine and its optimization design. Based on the unsteady evaporation characteristics inside UDMH (unsymmetrical dimethylhydrazine) organic gel droplet and the micro molecule structure of organic gel propellant, three kinds of liquid phase evaporation model, the unsteady multicomponent evaporation model, the interface tracking multiphase flow evaporation model and the discrete element multiphase flow evaporation model, are proposed. The unsteady multicomponent evaporation model regards the gel droplet as a binary multiconponent droplet, in which the gellant inside the gel droplet is been equivalent to a species with low volatility and high boiling temperature. In order to depict the shape and location variety of vapor bubble inside the gel droplet more precisely, the interface tracking multiphase flow evaporation model regards the gel droplet and the vapor bubble inside it as a single fluid, and uses the Level Set function tracking the interface location of vapor bubble. Based on the micro molecule structure of organic gel propellant, the discrete element multiphase flow evaporation model for the gel droplet regards the gellant and vapor bubble as the aggregation of micro-particles with different properties respectively, and uses the Lagrange method tracking the movement and aggregation of each kind micro-particle. The multicomponent evaporation model has been implemented in our foregoing work, so a summary of the model is presented. And next the main difficulties and the technique preparation about the last two multiphase flow models have been presented and analyzed in detail. In view of mixing and combustion process of gas phase surrounding the UDMH organic gel droplet, we propose that the finite rate chemical reaction model and the flamelet model should be used for the stagnation ambient and convective ambient respectively. The difficulties and numerical methods for handling the stiff chemical source term in finite rate chemical reaction model have been presented. And next the consistent flamelet model which takes consideration of species diffusion coefficient and non-unity Lewis number is presented. It would be more precise for the temperature and species interpolation of the gel droplet laminar non-premixed combustion flow field.