Turbulence measurements and observations of turbulent premixed flames at elevated pressures up to 3.0 MPa

Abstract

In order to explore the characteristics of turbulence and turbulent premixed flames in a high-pressure environment, a nozzle-type burner with a turbulence generator was installed in a high-pressure chamber. Turbulence measurements and combustion experiments were conducted with the chamber pressure up to 3.0 MPa. Methane-air mixtures were used for the combustion experiments and confirmed that the turbulent premixed flames were successfully stabilized. Flame observations were made using instantaneous Schlieren photographs and high-speed laser tomography. Turbulence measurements were conducted using a hot-wire anemometer installed in the high-pressure chamber. It was found that the scales of turbulence generated by perforated plates at elevated pressure are smaller than those at atmospheric pressure. From flame observations, the following features of the flames at elevated pressure were found: (1) wrinkled structures of the flames become very fine and complex, and the cusps become sharp as pressure rises;(2) the flamelet breaks at many points of the flames and the scales of broken flamelets become small; (3) small-scale parts of the flame front convex to the unburned mixture frequently occur and move quickly to the unburned side. The effects of ambient pressure on turbulence characteristics and possible mechanisms which produce the wrinkled structure of the fine scales and generate flame front disturbances in the high-pressure environment are discussed.