Development of "Tiny" Droplet Flame Simulator: "Super-Stabilized" Micro-Jet Flame in a Hot Air

Abstract

An attempt to form a "tiny" spherical flame over the small jet burner (so called microflame) as a model of a tiny droplet flame was made experimentally without any assistance brought by large facilities which could eliminate/minimize buoyancy effect. Using ceramic burner and high-temperature air effectively suppresses the quenching distance and such "super-stabilized" micro-jet flame would be fairly close to 1-D (droplet) flame. The temperature of air (up to 770 K) and the fuel (methane) flow rate were varied as experimental parameters. Fundamental characteristics of limiting and near-extinction behavior of methane-air microflame in high-temperature air are investigated. Results show that the flame shape under high-temperature air condition is hardly affected by the external disturbance and the quenching distance is minimized due to the increase of the temperature at burner tip. It is found that the theory developed by Kuwana et al., to predict the limiting behavior of small-scale flame would be applicable even for the one formed in high-temperature air. Minimum flame size achieved in high-temperature air is predicted as an order of hundreds micron; interestingly, this is identical to what is predicted with ideal adiabatic burner (i.e., no conductive and radiative heat loss to/from the burner) in our previous numerical work.