PHYSICS OF LAMINAR PREMIXED CH4 − O2 FLAMES AT CRYOGENIC CONDITIONS - A COMPUTATIONAL STUDY

Abstract

With increased commercial spaceflight activity, methane has found adoption

in the next generation of liquid rocket engines (LREs). In a liquid rocket engine with

cryogenic propellants, such as methane and oxygen, the propellants are stored in

their tanks at low temperatures. As they are injected into the combustion chamber

at high pressures, the fluid is close to its thermodynamic critical point where there

are drastic changes in fluid properties like density, heat capacity, surface tension,

and solubility. The ideal gas law is inapplicable at such extreme conditions, and

real gas thermodynamic and transport properties are required to accurately model

the combustion physics at supercritical conditions. Much of the previous work

applying real gas models in computational simulations of reacting flows have

focused on non-premixed flames or cold-flow mixing configurations. In this study,

we investigate the effects of real gas property estimation on planar, unstretched,

laminar premixed methane-oxygen flames at transcritical conditions.

The computational framework used in this study integrates real gas property estimation into the steady-state, freely-propagating flame solver available in the Cantera combustion suite. The Peng-Robinson equation of state provides thermodynamic property closure. High-pressure transport properties are modeled by the Chung and Takahashi correlations, respectively. The effects on laminar flame structure are presented. We find that enhanced real gas reactant densities have a significant impact on flame propagation, lowering flame speeds by a factor of ∼ 5 near the critical region. Real gas caloric properties lower mass burning rates by 10%. The consequence of using low-pressure transport properties with the Peng-Robinson EOS at variable Lewis numbers is discussed.