Slowly Turned to Smoke

Sfumato means "turned to smoke". A flame, with its cleansing heat, the purifying light of the blaze, followed by murky darkness, ash, filth, smoke. The change takes place in a heartbeat, but to truly understand, we must parse this small moment into a thousand smaller moments, zoom in to see the fractal details which exist, but are invisible to the naked eye. These details are hidden by size, cloaked with speed, and shrouded by chaos. But they can be perceived. The layers pulled back, the nuances exposed, and the subtlety laid bare. Here, in a series of high-speed videos, let us explore the unseen details of what happens when we turn to smoke.

 

Experimental Setup

Many thanks to LaVision and Dr. Callum Gray in Ypsilanti for the use of their high speed cameras, lasers, and image processing software.  LaVision provides test equipment for image-based measurements, along with unique sensors, probes, and devices for quantifying fast phenomena.  These videos were taken using a LaVision camera shot at 5000 images per second, a neodymium: Yttria Alumina Garnet laser, a Bic lighter, and a bottle of Gravitas, by Sfumato.

A Flame is Born

Summed over the last 2 decades, I estimate that I have carried a Bic lighter in my pocket for tens of thousands of hours. This little device brings the gift of fire to the masses.  Prometheus, thy name is Bic. You’ve no doubt seen someone light a lighter, but have you ever truly seen fire being born?

Spinning in Air

The spray from a bottle of fragrance is driven by pressure.  When the button is depressed, the pressure inside the bottle increases, forcing fragrance out the nozzle.  This liquid is ejected forcefully enough that it breaks into tiny droplets.  As the droplets vaporize and are resisted by the air, they take on certain patterns that can be illuminated with the proper imaging technique.

Laser Sheet Spray Imaging

For this video, I used a laser sheet to illuminate the spray.  Sheet illumination allows you to track individual droplets more clearly.  A high-speed camera is then synced with the laser at 5000 frames per second, and it’s lights, camera, action. As the spray exits the nozzle, you can see the large droplets at the beginning, before the spray really hits its stride.  Once into the heart of the spray, a double vortex forms at the leading edge.  This shape occurs because as droplets at the front slow down due to wind resistance, they are pushed out of the way by the speedier droplets behind, creating a vortex pattern.  In 3D, the pattern  resembles a smoke ring, being a fully circular vortex traveling in space.  After the bulk of the spray has passed, a vortex street appears, showing alternately rotating vortices within the bulk spray.

To Ashes 

Applying fuel to the flame, we see chaos unfold in all its glory.  Fragrance burns when it is mixed with the proper amount of air and ignited, and from this source, the flame front seeks a path on which to travel.  The journey of the flame is conflated with the turbulence of fragrance being sprayed, and what develops is one of the most complex phenomena in nature: turbulent combustion.  But out of complexity comes simplicity, as soon after the fiery rage all is peaceful again, the flame and fuel turned to smoke. 
 
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