Hydrothermal ethanol flames in Co-flow jets

Abstract

Results on the autoignition and stabilization of ethanol hydrothermal fames in a Supercritical Water Oxidation (SCWO) reactor operating at constant pressure are reported. The flames are observed as luminous reaction zones occurring in supercritical water; i.e., water at conditions above its critical point (approximately 22 MPa and 374 °C). A co-flow injector is used to inject fuel (inner flow), comprising an aqueous solution ranging from 20 %-v to 50 %-v ethanol, and air (annular flow) into a reactor filled with supercritical water at approximately 24.3 MPa and 425 °C. Results show hydrothermal fames are autoignited and form diffusion flames which exhibit laminar and/or turbulent features depending upon flow conditions. Two orthogonal camera views are used; one providing a backlit shadowgraphic image of the co-flow jet and the other providing color images of the flame. In addition, spectroscopic measurements of flame emissions in the UV and visible spectrum are discussed.

Review on an Advanced Combustion Technology: Supercritical Hydrothermal Combustion

“…The results showed that the speed increased with injection temperature. In comparison with a higher flame propagation velocity (0.4-3 m/s) in gas phase combustion, the hydrothermal flame propagation velocity varied from 0.01 to 0.1 m/s in the volumetric reactor, which was also consistent with the experimental results by M.C.Hicks [59]. However, it should be noted that due to the fact that the properties of the mixture in the supercritical state cannot be calculated accurately, there is still a deviation for the calculated value.…”

“…Ignition was the fourth stage in the whole process. Hicks observed the spontaneous ignition of the ethanol-water-air system injected by laminar flow had three stages: random spots, flash-back, and stabilization (see Figure 7) [59]. The results showed that the formation and disappearance of random hot spots might occur more than once before the stable flame was finally established.…”

“…Transition to the turbulence of buoyant near-critical water jets and the role of buoyancy [57] The characteristics of laminar and turbulent diffusion flame and the formation of soot [58] The auto-ignition and stability of ethanol hydrothermal flame [59] Indian Institute of Technology Roorkee, India Semi-batch rector…”

“…With visualization apparatus, Hicks obtained the propagation velocity of axial laminar diffusion of hydrothermal flame at both low air velocity condition (50 vol% ethanol of 2 mL/min, air of 2 mL/min) and high air velocity condition (50 vol% ethanol of 2 mL/min, air of 7 mL/min) [59]. At a low air velocity, the flame propagation velocity was basically stable, with average value about 4.6 cm/s.…”

“…The peak of the thermal expansion coefficient near the critical point theoretically reflects the important contribution of density to the buoyancy mixing that occurs during transcritical processes. M.C.Hicks pointed out that the transcritical process was a sign of the emergence of a large scale of buoyancy convections, and even small temperature differences (~1 °C) was to cause strong buoyancy effects [59]. They observed that the strong buoyancy convection started at 370 °C and disappeared at the temperature exceeding 400 However, sometimes heat transfer deteriorates and the convective heat coefficient plunges sharply [110].…”