New extensions of a semi-detailed chemical kinetik model for sustainable aviation fuels: A study on C8-iso-alkanes

Abstract

Sustainable aviation fuels (SAF) are a promising solution for reducing greenhouse gas emissions in aviation. Fuel design strategies have been demonstrated to enable optimizations with respect to safety, performance, and emissions, based upon the chemical composition of the fuel. The chemical class of iso-alkanes is a typical component of many SAFs and exhibit complex combustion behavior. This is a major challenge in the technical assessment of these fuels as the combustion characteristics of iso-alkanes is strongly dependent on their molecular structure. Accurate chemical kinetic models are essential to assess their potential as sustainable fuels. The systematic knowledge of this behavior is needed to enable the prediction of combustion characteristics without the need for extensive experimental investigations. At the given moment, many existing chemical kinetic models lack the necessary detail to accurately capture these structural variations of the iso-alkanes, limiting their predictive capability for SAF characterization. This study aims to investigate iso-alkanes systematically and include them into the DLR Concise model to enhance its ability to predict SAF combustion properties. The DLR Concise model is a semi-detailed mechanism designed to cover a range of technical fuels. In particular, this study focuses on two C8-iso-alkanes: 2-methylheptane and 2,5-dimethylhexane , with different degrees of branching to systematically analyze the effect of molecular branching on fundamental combustion properties. The branching effect of these two iso-alkanes is compared to iso-octane, which is already present in the mechanism. A key challenge is the effective lumping of species, to ensure that the extended mechanism retains its essential semi-detailed character, while maintaining its predictive capability comparable to the detailed mechanisms. The extended model is validated against both literature data and in-house experimental data, including a wide array on ignition delay times, laminar flame speed and species profiles from jet-stirred reactors. The extended chemical kinetic model consistently reproduces the experimental data, for both high and low temperature chemistry.