Transition of characteristic explosion limits: From hydrogen to diethyl ether

In this work, the explosion limits of three different fuels: hydrogen (H2), propane (C3H8, C3), and diethyl ether (DEE, C2H5OC2H5, C4), are investigated based on detailed chemical kinetics. The results reveal that the explosion limit of H2-O2 exhibits the typical Z-shape, while C3H8-O2 exhibits a single-NTC response, and DEE-O2 displays a double-NTC response. Sensitivity analysis indicates that the appearance of the NTC response in both the C3 and DEE fuels is intricately linked to low-temperature reaction paths. Moreover, the extents of the NTC responses are comparable for these two fuels with similar low-temperature reaction paths, but operate under different tem-perature conditions. Specifically, the double-NTC response observed in DEE is attributed to its primary C-H and C-O bonds, generating C4 and C2 radicals. The oxygen addition and the subsequent pathways of these radicals dominate in distinct temperature ranges. In contrast, C3H8 only possesses the C-H bond, resulting in a single-NTC response, as OH radicals are mainly released by C3 radicals through oxygen addition, isomerization, and decomposition reactions. The results of binary fuel mixtures with H2 addition indicate that the reactivity of H2 controls the low-pressure and high-temperature regime, while the C3 and DEE fuels dominate the high-pressure and low-temperature regime. Additionally, a triangular crossover regime is identified between these two regimes due to the switchover of the reactivity. Sensitivity analysis further reveals the transition of the dominating re -actions related to different fuels at various pressure-temperature regimes. Finally, based on the explosion limits of the multi-component mixtures, a detailed explosion regime diagram is proposed for carbon-free fuel (H2), alkane fuel (C3H8), and oxygenated ether fuel (DEE). This new regime diagram provides valuable insights for the investigation and utilization of ether fuels and the mixture of different fuels.