Research on Minimum Ignition Energy Testing of Normal-Alkane Vapors and Its Dependence on Carbon Chain Length

Abstract Minimum Ignition Energy (MIE) is a critical parameter for assessing the combustion and explosion risks of liquid fuels under specific conditions. However, systematic testing methods for long-chain alkanes remain underdeveloped. In this study, an experimental apparatus was developed based on American Society for Testing and Materials Standard ASTM E582-21 to measure the MIE of liquid fuel vapors. Significant improvements in ignition energy control precision were achieved by effectively mitigating vapor condensation. Furthermore, the relationship between MIE and carbon chain length in long-chain alkanes was investigated. System sensitivity parameters were calibrated using methane/air and propane/air mixtures, establishing optimal testing conditions as a 2.0 mm electrode gap and a 14.0 pF capacitance. The reliability of the system was validated through MIE measurements of C₅–C₈ alkanes (n-pentane, n-hexane, n-heptane, and n-octane), yielding values of 0.197 mJ (at 3.4 vol%), 0.253 mJ (at 3.3 vol%), 0.303 mJ (at 3.0 vol%), and 0.323 mJ (at 2.8 vol%), respectively. These results show less than 5% deviation from literature values and a relative error below 8%. Extended measurements of C₉–C₁₁ alkanes revealed MIE values of 0.523 mJ (at 2.8 vol%) for n-nonane, 0.857 mJ (at 2.5 vol%) for n-decane, and 1.127 mJ (at 2.0 vol%) for n-undecane. Notably, the results demonstrate a substantial increase in MIE with carbon chain length, showing a 471% rise from C₅ to C₁₁. A nonlinear regression analysis confirmed a strong correlation between MIE and carbon chain length (R² = 0.98).