Development and Fidelity Evaluation of a Skeletal Ethylene Mechanism under Scramjet-Relevant Conditions

Abstract

As one of the major short chain hydrocarbons resulting from the cracking process, ethylene is often used as a surrogate for cracked kerosene. In this study, a skeletal mechanism of ethylene was developed under the typical working conditions of scramjet combustors. The skeletal mechanism was reduced from a fully verified detailed mechanism under the desired working conditions. An integrated reducing method containing directed relation graph with error propagation method (DRGEP), sensitivity analysis (SA), and computational singular perturbation (CSP) was employed to obtain three skeletal mechanisms. A three-level fidelity validation of the skeletal mechanisms respectively comparing the kinetic properties, the global combustor performance, and the detailed flame structure was proposed to comprehensively evaluate the skeletal mechanisms. In the first-level fidelity validation, the three skeletal mechanisms all show good agreement with the detailed one in the autoignition delay and laminar flame speed over a wide range of working conditions. Then in the second-level fidelity validation, the smallest mechanism consisting of 24 species and 86 reactions (24S/86R) was further validated through incorporating with the large eddy simulation of a realistic scramjet combustor. Comparisons with the experimental data and the predictions by the detailed mechanism show that the global combustor performance (e.g., pressure, Mach number, and combustion efficiency) was accurately predicted by the 24S/86R mechanism. In the third-level fidelity evaluation, the flame structure characterized by the distribution of CO, OH, and heat release rate was analyzed through comparing the predictions by the 24S/86R mechanism with those by the detailed one during which the insufficiency of the skeletal mechanism was also recognized.

Development of Skeletal Kerosene Mechanisms and Application to Supersonic Combustion

“…Then = 0.09 36,[39][40][41][42][43] . The solver has been applied to various scramjet combustor cases 25,26,28,44 to examine its accuracy and robustness in the modeling of complex supersonic combustion.…”

UQ eSpace

“…Due to difficulties with accurate measurements in experimentation, there is insufficient knowledge detailing the internal flow, mixing, ignition and combustion processes of scramjets engines at high Mach number flow conditions (Wu et al, 2017). Adequate transient flow simulation of the ignition and combustion of hydrocarbons in scramjet conditions requires high accuracy numerical schemes as well as qualified turbulence and finite rate chemistry models.…”

“…Due to these limitations it is desirable to develop accurate numerical simulations for the ignition of hydrocarbons in scramjet engines. ethylene and kerosene (Ladeinde and Li, 2018) Kerosene itself is a mixture of hundreds or even thousands of hydrocarbons making it impossible to use in its original state for numerical modeling purposes (Wu et al, 2017). However, methane (CH 4 ) and ethylene (C 2 H 4 ) are short chain hydrocarbons that are major products resulting from thermally cracked kerosene.…”

“…Additionally, fuel components with dramatically different chemical properties such as methane and ethylene can be used as surrogate mixtures for more complex fuels (Luo et al, 2011). As a result methane and ethylene are often used as surrogate fuels in both simulations and experimentation (Wu et al, 2017).…”

“…Detailed chemical kinetic mechanisms are advantageous in the sense that they work for a broad range of general conditions and provide accurate calculation of key reaction parameters (Løvås, 2009). However, detailed mechanisms for ethylene and methane contain hundreds of species with hundreds to thousands of elementary reactions (Wu et al, 2017). Lu and Law (2009) makes the observation that there is an approximately linear correlation between the number of species and number of reactions in chemical mechanisms N r ≈ 5N s where N s is the number of species and N r is the number of reactions.…”