Abstract
The present work focuses on the numerical modeling of combustion in liquid-propellant rocket engines. Pressure and temperature are well above thermodynamic critical points of both the propellants and then the reactants show liquid-like characteristics of density and gas-like characteristics for diffusivity. The aim of the work is an efficient numerical description of the phenomena and RANS simulations were performed for this purpose. Hence, in the present work different kinetics, combustion models and thermodynamic approaches were used for combustion modeling first in a trans-critical environment, then in the sub-critical state. For phases treatment the pure Eulerian single phase approach was compared with the Lagrangian/Eulerian description. For modeling combustion, the Probability Density Function (PDF) equilibrium and flamelet approaches and the Eddy Dissipation approach, with two different chemical kinetic mechanisms (the Jones-Lindstedt and the Skeletal model), were used. Real Gas (Soave-Redlich-Kwong and Peng-Robinson) equations were applied. To estimate the suitability of different strategies in phenomenon description, a comparison with experimental data from the literature was performed, using the results for different operative conditions of the Mascotte test bench: trans-critical and subcritical condition for oxygen injection. The main result of this study is the individuation of the DPM approach of the most versatile methods to reproduce cryogenic combustion adapted for different operating conditions and producing good results.
Highlights
To enhance the performance of liquid-propellant rocket engines, combustion occurs in a high-pressure combustion chamber
Jones-Lindstedt mechanism [27] (JL): it is a multi-step reaction scheme that originally was dedicated to the combustion of methane/air mixtures; in the present work it was utilized in the Frassoldati [28,35] version that involves nine species and six reactions and regards the combustion of methane with pure oxygen; Detailed Skeletal mechanism from Grimec 3.0 [19,20,21] (SKEL): it is a reduction of the detailed
Liquid oxygen and gaseous methane are driven in the combustion chamber separately and under different conditions: methane is in a gaseous state while oxygen is in a trans-critical (G2 test case) or subcritical (G1 test case) condition
Summary
To enhance the performance of liquid-propellant rocket engines, combustion occurs in a high-pressure combustion chamber. The main problems in cryogenic combustion modeling are connected with the particular behavior of the liquid oxygen spray that presents intermediate characteristics between a turbulent gaseous jet and a liquid spray and both the aspects have to be taken into account in the interpretation of the behavior of the phenomena under investigation [2] Both thermodynamic and kinetic models have to be applied to try to accurately reproduce the real phenomenon. Experimental tests [7] reveal that the injected propellant has a hybrid structure between a turbulent gaseous jet and a liquid spray This makes it more difficult to numerically treat the real phenomenon and it is necessary to test different numerical strategies as in the present work. The simulation of the effects of different distributions of the droplets at the inlet in the DPM cases has been carried out
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