Consolidated Description of Explosion Limits and Ignition Delays: Hydrogen and C1-C7 N-Alkanes

This study computationally investigates the auto-ignition delay times and explosion limits of H2/O2 and C1-C7 n-alkanes/O2 mixtures based on detailed chemical kinetics. Comprehensive ignition responses are consolidated through three-dimensional response surfaces of the ignition delay time as function of the system temperature and pressure, yielding the essential kinetic characteristics governing ignition. The intersection curves of the ignition surface with the cross-section perpendicular to the three coordinate axes are the characteristic response curves of the ignition delay time and explosion limit. Therefore, the ignition delay time and explosion limit are the changing characteristics of the three-dimensional ignition surface observed from different perspectives. Sensitivity analysis demonstrates that while the significant variations of the reaction pathways among different fuels are the primary reason of the wide spreading of the explosion limits curves for the various fuels in the low-temperature regime, their chain branching reactions tend to be similar in the intermediate temperature regime such that the explosion limit curves of different fuels are closely coalesced. Furthermore, in the high-temperature regime, the chain branching reactions of alkanes are primarily governed by small radicals, such as CH3, while it is still dominated by the H+O2=OH+O for H2.