Session: ASME Undergraduate Student Design Expo

Paper Number: 167151

Single Droplet Combustion of Alternative Fuel Mixtures 

As the demand for lower emissions grows, interest in alternative fuels has increased, making research into their viability increasingly important. Biofuels such as biodiesel and ethanol are already used in transportation, but biodiesel remains more expensive than hydrocarbon fuels, and ethanol suffers from low energy efficiency. Currently, biofuels alone aren’t efficient enough to replace conventional fuels entirely. Additionally, their production process generates byproducts at various stages, such as glycerol from biodiesel and surplus alcohols like methanol from ethanol production. This study investigates the combustion properties of conventional and alternative fuels, as well as their mixtures, to optimize performance.

 

A suspended droplet combustion method was used to analyze the burning characteristics across three droplet size ranges (0.60-1.40 mm), capturing combustion at key stages: preheating, swelling, and burning. This study aims to assess how well alternative and conventional fuel mixtures adhere to the  law and explore the effects of mixing. Previous research showed that fuels such as ethanol, methanol, glycerol, and algal oil exhibited micro-explosion, while hydrocarbon fuels primarily swelled and followed the  law. For instance, the 35% glycerol-methanol mixture demonstrated increased micro-explosions, and a faster burning rate compared to their base components, where 60% glycerol-methanol followed the  law much more closely. This study expands on prior work by identifying combustion “breakpoints” in fuel composition, testing additional volume ratios, and determining optimal mixture conditions to enhance combustion efficiency.

 

The suspended droplet combustion method mentioned earlier consists of suspending the fuel droplets on thin fibers and arranging the ignition source to be as close as possible to the droplets without interfering with burning. The fibers used are 16-micron silicon carbide fibers, boasting a high thermal conductivity while being small enough to assume spherical symmetry while the droplet burns. To achieve the combustion of the suspended fuel droplets, an actuator-mounted hotwire system was used. Where the hotwires were mounted onto linear actuators to retract as soon as the droplet starts to burn, to keep from interfering with the  law and the data collection process. Likewise, data collection was conducted using two macro cameras, one monochrome and one color. The monochrome images were used to take measurements of the droplet size from the pixel count of the images. Color images were used to track the flame’s combustion characteristics: soot shell formation, flame intensity, and color. Data processing was done in an older NASA software called spotlight, which with human input can track the diameter of the burning droplet and translate that into graphable data tables to determine the adherence of the droplets to the  law. In the future an AI based software called Annolid will be used for data processing to extrapolate the process and allow more consistent data collection to occur, without human interference.

Presenting Author: Joseph Sanders University of Tennessee at Chattanooga

Presenting Author Biography: I am currently an undergraduate research assistant at the University of Tennessee at Chattanooga. I'm a mechanical engineering major with a vested interest in the creative side of engineering, as well as anything relating to heat transfer, energy, and fluid mechanics. I enjoy mechanical engineering for the sheer variety that exists if you have drive to find it, the sky isn't even the limit here, and that's what makes it wonderful. This will be my first research project to present on that is truly my own and I'm immensely excited, I have a passion for alternative fuels and green energy, thus this flavor of career development gets me ever closer to working in the places I truly want to be.

Authors:

Joseph Sanders University of Tennessee at Chattanooga