Technical note: Extension of full-spectrum correlated k-distribution look-up tables to CH4 and NH3 for use in combustion modelling

Abstract

Due to reliable accuracy and computational efficiency, full-spectrum correlated k-distribution (FSCK) look-up tables (short for traditional FSCK tables) have continuously gained popularities; however, they are only valid for combustion products and intermediates, such as CO₂, H₂O, CO and soot. Gas fuels, i.e., CH₄, NH₃ or their mixture, also display complex spectral or ‘nongray’ behaviors across spectrum. While those gas fuels are commonly consumed during combustion, their spectral behaviors may affect ignition, flame spread and chemical reactions. Therefore, it is necessary to include spectral properties of both CH₄ and NH₃ into FSCK look-up tables. To achieve this, a separate FSCK look-up tables (short for extended FSCK tables) including only CH₄ and NH₃ is constructed in this work. The multiplicative mixing scheme is then used to mix k-distributions from traditional FSCK tables and those from extended FSCK tables. A realistic non-premixed flame is used to validate both efficiency and accuracy of extended FSCK tables as well as multiplicative mixing scheme. Results show that absorption from CH₄ and NH₃ during combustion is strong and cannot be ignored. Results also show that treating spectral properties of CH₄ and NH₃ to be gray may bring in significant errors.