Investigating the transformation relationships and key parameters influencing explosion characteristics

Abstract

The auto-ignition delay times (IDT) and explosion limits (EL) are two important parameters describing the chemical reactivity of fuels, but their relationship has not been clearly revealed. The IDT and EL curves for a specific fuel only contain three parameters: residence (or ignition) time, pressure, and temperature, so their relationship can be revealed through these parameters. Specifically, the explosion limit curve can be obtained by collecting the intersection P-T state of the constant ignition time line with the ignition delay curves under different pressures on the IDT diagram—and vice versa. The ignition delay curves of H₂, methane, ethane, and propane with flattened Z-shaped, approximate linear shape, ZTC (zero temperature coefficient), and NTC (negative temperature coefficient) responses are successfully converted to explosion limit curves with typical Z-shaped, approximate linear shape, ZTC, and NTC responses using this conversion method, respectively. Furthermore, as the equivalency ratio rises, the IDT and EL curves of H₂ rotate counterclockwise around an anchor point, as the first and third explosion limits of H₂-O₂ are influenced by the concentration of O₂ and H₂, respectively. For the C₃H₈-O₂ mixture, a higher equivalence ratio enhances fuel-involved reactions, resulting in a shift of the IDT and EL curves toward lower IDTs and lower pressure regimes. Moreover, the addition of N₂ lowers fuel and O₂ concentrations, reducing overall reactivity. The proposed transformation relationship between IDT and EL curves exhibits universality across fuels, enabling direct derivation of pressure–temperature EL data from IDT diagrams and vice versa.