Garrett Gerchar, Ivan Komodore, Justin Truong
Team first is the first group requirement in this class with the intent being to capture flow as a group as many of these projects require several simultaneous actions to be carried out such as initiating the flow, preparing lighting and operating the camera. Our team opted to demonstrate flow in flames for our first project as they can create very interesting flows and colors with a great variety of combinations available. In this specific photo, I wanted to capture air movement around a fuel source after ignition to see how the flame reacts to a horizontal air flow. Additionally the different layers within the flame clearly display the layers of flow as well as temperature gradients.
In this picture, the fuel source is moving from the photographer’s right to left at an approximate speed of 1m/s. I think that one of the most interesting aspects is that you can clearly see how gasses are moving around the fuel and the various temperatures can be clearly seen as well. Flow, in this case, is laminar and the layering can be clearly seen in the brightness of the flame. If the flow was turbulent, we would see characteristics typical of that type of flow where flame would curl and eddies within the flame would be visible. The darker ares of the flame are the coolest regions where gasses are moving relatively quickly and cooling the particles within. As the gasses recombine approximately 1″ from the fuel source, they slow down and are heated by the reaction of the alcohol, paper and air. As the alcohol and paper burn, they release microscopic particles in a process called vaporization. These small particles react with oxygen in the air, generating more heat and combustion byproducts. This is the primary reaction zone and the process of combustion in this zone is called pyrolysis or fuel cracking . As the fuel burns, it produces microscopic carbon particles that combine into soot. The yellow flame is caused when these oxidants are heated and the electrons in the atoms are excited to higher levels. The color of the flame is dependent on the fuel source, temperature and the efficiency of the reaction. Since this is displaying a yellow flame, we know that soot is being created by incomplete combustion. If the reaction was complete and all of the reactant used up entirely, we would see a blue colored flame instead .
As the gasses are heated, they become less dense than the ambient air causing them to rise rapidly. This effect can be seen as the flame turns upward on the right side of the picture. Eventually, the gasses cool which causes the soot particles to emit light, fading from white to yellow to orange. The particles lose energy until they end up in their base state and are no longer capable of releasing visible light as they exit the path of the flame to the rear of the flow.
All of the images in our series were taken inside a dark garage. The main and side doors were cracked at all times and opened fully at regular intervals to ensure that the air inside was properly ventilated. Additionally, a charged garden hose was kept within a close distance to extinguish any unwanted or uncontrolled flames should they arise. The fuel source in this image is a rolled paper towel that had been soaked in isopropyl alcohol. The rolled paper towel was then inserted into a tube approximately 1/2″ in diameter and 4′ in length. We then ignited the paper towel with a BBQ lighter and one of my teammates waved the tube back and forth horizontally so that the fuel source moved at approximately 1m/s. I captured the picture while facing my teammate from about 8′ away so that I could display the horizontal flow.
This image was captured using a Sony A6300 camera with a 16-50mm, f/3.5-5.6 zoom lens. For this picture, the camera was approximately 4′ away from the flame with the focal length set to 36.00mm (equivalent to 54mm on a full frame sensor) and an aperture of f/5.6. Shutter speed was 1/1000s to reduce motion blur as much as possible without being so fast that an unreasonable amount of ISO was required. ISO was set to 6400, so a small amount of noise is present but not so much as to reduce the quality of the image to a distracting level. A small amount of post-processing was done to this picture to better demonstrate the flow. The vibrancy and contrast were increased and the blacks were deepened using the transfer function to remove some ghosting in the background and to better isolate the flame.
Overall I am pleased with the result of this project, the end result looks very nice and displays the flow well. If I were to attempt to improve upon the idea, I would try using different fuel sources and alter the size of the flame to see how the end result changes. This may be able to demonstrate some different colors as well as some turbulence within the flame.
I realize that I could have cropped it to make the fire more central within the image but I left it as it came from the camera since I felt like the additional black space gave the fire a better sense of motion.
References Jozef Jarosinski, Bernard Veyssiere “Combustion Phenomena: Selected Mechanisms of Flame Formation, Propagation and Extinction”, CRC Press, Feb 12, 2009
 C. H. Kim, A. M. El-Leathy, G. M. Faeth and F. Xu, “Laminar Soot Processes Experiment: Findings From Ground Based Measurements”, NASA, 2003