Unsteady non-premixed methane/oxygen flame structures at supercritical pressures

Unsteady non-premixed flame structures of methane/oxygen mixtures are investigated at supercritical pressures, representative of liquid rocket engines combustion chamber operating conditions. A general-fluid formulation of the flamelet equations is used and deviations from ideality of the thermodynamic properties are taken into account by means of a computationally efficient cubic equation of state written in a general three-parameter fashion. The effects of pressure and scalar dissipation rate are investigated in the context of prototypical unsteady laminar flame configurations, such as autoignition and re-ignition/quenching. In auto-igniting flamelets, real gas effects are observed to influence different flame regions depending on the thermodynamic pressure. Moreover the mixture ensuing from methane oxidation is never observed to reach a saturated (two-phase) thermodynamic region. Re-ignition and quenching phenomena are analyzed using a time dependent forcing function for the scalar dissipation rate, in order to investigate the response of the real gas flame structures to typical turbulent perturbations. The role of pressure on the critical strain values that a real gas laminar flame can sustain without quenching is investigated and compared to its ideal gas counterpart.

本数据集针对贴合液体火箭发动机燃烧室实际工作工况的超临界压力条件，开展甲烷/氧气混合燃料的非定常非预混火焰结构（unsteady non-premixed flame structures）研究。本研究采用小火焰方程（flamelet equations）的通用流体形式，并通过计算效率优异的通用三参数立方型状态方程（cubic equation of state），考量热力学性质的非理想性偏差。研究针对典型非定常层流火焰构型展开，涵盖自燃（autoignition）、复燃/淬熄（re-ignition/quenching）场景，探究压力与标量耗散率（scalar dissipation rate）的影响规律。在自燃小火焰中，观测到真实气体效应（real gas effects）会依据热力学压力影响火焰的不同区域；此外，甲烷氧化生成的混合气体始终未进入饱和（两相）热力学区域（saturated (two-phase) thermodynamic region）。为探究真实气体火焰结构对典型湍流扰动（turbulent perturbations）的响应特性，本研究通过对标量耗散率施加时变强迫函数，对复燃与淬熄现象展开分析。本研究还探究了压力对真实气体层流火焰可维持而不发生淬熄的临界应变值的影响，并将其与理想气体（ideal gas）工况下的结果进行对比。