Numerical Investigation of Coaxial GCH₄/LOx Combustion at Supercritical Pressures

ABSTRACT

This article aims to numerically investigate the combustion phenomenon of coaxial gaseous CH₄/LOx at supercritical pressures. The choice of turbulence model, real gas model, and chemical kinetics model are the critical parameters in numerical simulations of cryogenic combustion at high pressure. At this supercritical operating pressure, the ideal gas law does not remain valid for such cases. Therefore, we have systematically carried out a comparative study to analyze the importance of real gas models, turbulence parameters, and chemical kinetics at such conditions. The comparison of real gas models with the NIST database reveals better conformity of SRK (Soave Redlich Kwong – Equation of State (EoS)) model predictions with the database. Further, the computed results indicate that the Standard k-ε turbulence model with modified constant (C_ε1 = 1.4) captures the better flame shape and temperature peak position compared to other RANS based turbulence models while invoking the non-premixed steady β-PDF flamelet model for simulating the combustion process. Furthermore, a comparative study comparing two different chemical kinetics models indicates that the reduced Jones-Lindstedt mechanism (JL-R) can accurately predict the flame characteristics with the least computational cost. Finally, we have studied the effect of chamber pressure and LOx inlet temperature on the flame characteristics. The flame characteristics exhibit a strong sensitivity toward the chamber pressure due to the weakening of the pseudo-boiling effect with an increase in pressure. As a consequence of lower turbulent rates of energy and mass transfer through the transcritical mixing layer, the flame spreading becomes narrower at elevated pressure and temperature, thereby yielding an increased flame length at transcritical conditions.

KEYWORDS:

• Pseudo boiling
• pressure
• steady β-PDF flamelet model
• Soave Redlich-Kwong model

Acknowledgments

Financial support for this research is provided through IITK-Space Technology Cell (STC). The authors would like to acknowledge the IITK computer center (www.iitk.ac.in/cc) for providing the resources to perform the computation work, data analysis, and article preparation.

Compliance with Ethical Standards

We wish to confirm that there are no known conflicts of interest associated with this publication.

Additional information

Funding

This work was supported by the Indian Space Research Organisation [STC /ME /2018048].