Vaporization of liquid droplets in supersonic flow
The vaporization of liquid droplets in supersonic flow is studied experimentally. This problem has implications for the "cold start" phase of a hydrocarbon scramjet cycle, where liquid fuel can be injected into the combustion chamber. In this experiment discrete droplets are injected into a small-scale, supersonic wind tunnel. Under certain conditions it is possible to have droplets at a supersonic Mach number relative to the surrounding supersonic flow. Unheated liquid droplets can become superheated as they are injected into the relatively lower static pressure environment of a supersonic stream. This superheat in turn leads to accelerated droplet disruption and vaporization. The droplet behavior is examined using high-speed direct close-up and multiple-exposure imaging.
Schematic of draw-down wind tunnel and 2D under-expanded jet
Photograph of the experimental setup
Schlieren Image of 2D under-expanded jet and validation of supersonic flow in the under-expanded jet as demonstrated by presence of bow shock
Test fluid streamline upon injection and Plateau-Rayleigh instability formation
(d = 100±5µm, f = 3300Hz)
Mach numbers of droplets relative to the surrounding supersonic air stream.
The Mach disk is located 11 mm downstream of the nozzle throat
Measured droplet velocities in supersonic flow
2-Propanol Droplets at Distance from Throat.
I) Deformation II) Initial Breakup III) Primary Breakup IV) Total Breakup
LIF images for 2-propanol (left) and Hex-Pen 50/50 (right)