Miniature Supersonic Burner for the Study of Combustion at Extreme Conditions. I: Internal Flow

Abstract

A miniature supersonic burner has been designed with the purpose of studying extreme flow-chemistry interaction. The system combines a first-stage, a lean premixed methane/air burner that creates a vitiated flow at elevated pressure, and a second stage where additional fuel (methane) is added into the flow before exiting the system through a converging nozzle. At the system exit, a sonic underexpanded jet is created where very short characteristic fluid time scales obtain. These are comparable to the fastest chemical reaction time scales, thus creating a situation where the flow interacts with the chemistry and suppresses combustion. In this paper, reduced-chemistry three-dimensional computational fluid dynamics is used to understand the reacting flow in the system and predict flame holding, while vibrational Raman line-imaging spectroscopy is used—qualitatively—at the burner exit. Experiments and computations point to a clear bimodal behavior of the system: in one extreme, where an attached non-premixed flame is created in the burner; in the other extreme, where no reaction is taking place in the second stage and all additional fuel is left unburnt.