Structures of Laminar Methane/Nitrogen/Oxygen, Methane/Oxygen and Methane/Liquid Oxygen Counterflow Flames for Cryogenic Conditions and Elevated Pressures

Abstract

Abstract The understanding of physical and chemical processes occurring in many applications in sciences and engineering is important to ensure stability and efficiency of their performance. Examples are the combustion process in direct-injection engines, gas turbine combustors, and liquid rocket propulsion systems. The objective of this paper is the numerical investigation of laminar methane/air and methane/oxygen flames where different mixtures of nitrogen and oxygen in the oxidizer stream are studied. Moreover, liquid oxygen (LOX) spray flames with carrier gas methane directed against a methane stream are investigated in the counterflow configuration. These structures may be used in (spray) flamelet library or flamelet generated manifold computations of turbulent combustion. The mathematical model is based on two-dimensional equations which are transferred into one-dimensional equations using a similarity transformation. The numerical simulation concerns the axisymmetric configuration with an adaptive numerical grid for the gas phase. Detailed models of all relevant processes are employed; in particular, a detailed chemical reaction mechanism is used which comprises 35 species including C2 involving 294 elementary reactions. The thermodynamic data for CH4 and O2 below 300K are implemented for normal and elevated pressures. For the CH4/air and an oxygenated flame, the present results are compared with results from literature. The CH4/O2 flame is studied for elevated pressures up to 2MPa. Extinction conditions are evaluated for use in turbulent flamelet computations. It is shown that oxygen dilution, pressure, and strain rate have a pronounced effect on flame structure. The use of liquid compared to gaseous oxygen strongly affects flame structure.