Abstract
This article investigates the ignition of hydrogen/air and methane/air premixed flames in a laboratory scale experiment. It focuses on an initial characterization of the ignition transient sequence comparing the effects of fuel, equivalence ratio, and bulk velocity as well as geometry (bluff-body vs swirler, confined or unconfined). Transient evolution of the flame through high-speed flame chemiluminescence imaging are recorded for selected pre-mixture injector bulk velocities ranging from 5 to 15 m/s in the lean equivalence ratio range. Additional high-speed data include schlieren imaging. The chemiluminescence data are utilized to generate integrated flame light time-series to estimate ignition delay time. A comparison of the experimentally determined ignition delay time is conducted with results from literature and chemical kinetic data. The observed differences are discussed. Results from the high-speed schlieren imaging at speed up to 140 000 frames per second (fps) capturing the spark ignition dynamic sequence are documented next for three specific cases. These selected ignition transient sequences leading to stabilized flames are characterized in the premixed turbulent combustion flamelet regime near unity Karlovitz number. The flame front is tracked by identifying flame edges as the flame surface expands during the earliest instants of the ignition sequence. The method documented in this article is an initial step that can be used in future work to describe the evolution from ignition to flame stabilization. This work is motivated to fill the gap on ignition studies in the fully premixed regime and especially for hydrogen/air premixture where spark igniter is utilized.
