Highlighting the Role of Lubricant Oil in the Development of Hydrogen Internal Combustion Engines by means of a Kinetic Reaction Model

Abstract

The urgent need to reduce the dependence on fossil fuels has re-ignited the interest toward Hydrogen Internal Combustion Engines (HICEs). Nevertheless, there are still criticalities that need to be assessed for accelerating the development of this technology. The undesired but unavoidable participation of lubricant oil to the combustion process can be the cause of many of these. Due to an extremely low autoignition resistance at low temperatures, lubricant oil is considered the main responsible for the onset of abnormal combustion modes, which need to be understood for delivering reliable and ready to market HICEs. By employing a kinetic reaction mode, this work analyses the autoignition tendency of hydrogen contaminated with n-C16H34 (n-hexadecane), the latter being selected as a surrogate species representative of lubricant oil chemical characteristics. Starting from the detailed CRECK model (Version 2003), a reduced mechanism with very small size (169 species and 2796 reactions) was developed, which makes it suitable for the use in practical CFD engine simulations. Zero-dimensional numerical simulations were performed employing the reduced mechanism to quantify the variation of hydrogen ignition delay time due to the presence of different amounts of lubricant oil. Operating conditions typical of engine chambers were considered in the analysis. The results show that lubricant oil can have a significant impact on the charge reactivity, especially in the low-temperature range, with consequences that can potentially hamper the development of HICEs.