A Transition of Ignition Kernel Delay Time at the Early Stages of Lean Premixed n-Butane/Air Turbulent Spherical Flame Propagation

This paper explores the effects of root-mean-square turbulence fluctuation velocity (u?) and ignition energy (Eig) on an kernel delay time (?delay) lean premixed n-butane/air spherical flames with effective Lewis number Le ? 2.1 >> 1. Experiments are conducted in a dual-chamber, fan-stirred cruciform burner capable generating near-isotropic negligible mean velocities using pair cantilevered electrodes sharp ends at fixed spark gap 2 mm. ?delay is determined critical flame radius minimum speed during early stages laminar turbulent propagation. Laminar energies (MIEL MIET) measured 50% ignitability, where MIEL = 3.4 mJ increasing slopes MIET u? change from gradual to drastic when > 0.92 m/s (MIE transition). In quiescence, transition observed, decrement becomes rapid (modest) Eig less (greater) than MIEL. For cases, applying MIET, reverse trend MIE found for versus results same m/s. These indicated that could reduce one hand, but require higher (or other hand. Moreover, rising specific range, ? MIE, shorten ?delay, contribution as MIE. may play important role achieve optimal combustion phases design system engines operated under lean-burn conditions.