Numerical Investigation of Coaxial GCH4/LOx Combustion at Supercritical Pressures

TL;DR

This study numerically investigates coaxial GCH4/LOx combustion at supercritical pressures, emphasizing the importance of real gas models, turbulence, and chemical kinetics in accurately simulating flame behavior.

Contribution

It systematically compares real gas models, turbulence models, and chemical kinetics to identify optimal simulation parameters for supercritical cryogenic combustion.

Findings

SRK model aligns best with NIST database.

Standard k-e turbulence model captures flame shape effectively.

Reduced Jones Lindstedt mechanism predicts flame characteristics with low computational cost.

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-e turbulence model with modified constant captures the better flame shape and temperature peak position compared to other RANS based turbulence models while invoking the non-premixed steady b-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 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 towards 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.