The combustion characteristics of single fuel droplets of soybean oil (SBO) and butanol binary blends simply mixed by volume were experimentally examined. The droplets were supported at an intersection of microfibers in a 100°C combustion chamber at atmospheric pressure in normal gravity. Ignition was achieved via a hot wire igniter. Ignition characteristics and burning behaviors including burning to completion, burning with microexplosion and incomplete combustion were analyzed for initial concentrations ranging from 25–75% butanol. Droplet size and temperature measurements were analyzed throughout the droplet lifetimes. Relative concentrations prior and during combustion were estimated. Temperature measurements at ignition and above the burning droplet were analyzed. The addition of butanol significantly lowered the droplet ignition temperature. All mixtures studied ignited similarly to pure butanol droplets. The results showed consistency with closed-cup flashpoint temperatures of butanol-soybean oil blends. A three-staged burn including a microexplosion was observed for all mixed droplets, which burned completely. The disruptive burning proved to be a result of a diffusion limited gasification mechanism that has been previously linked to bi-component droplets with high volatility differentials. Microexplosions occur as a result of homogeneous nucleation due to superheating of the more volatile component trapped within the droplet at flame shrinkage. Results show that more butanol is burned in the first stage for Bu75 droplets resulting in microexplosions occurring late in the combustion process. For droplets of near equal initial concentrations, the microexplosions occur earlier resulting in less fuel burned in the first stage of combustion and therefore higher concentrations of butanol trapped within the droplet at flame shrinkage. Consequently these mixtures experience more microexplosions and at a greater intensity. The reduced tendency for Bu75 droplets to experience microexplosions suggest that the maximum droplet surface temperature may be depressed compared to droplets of near equal concentrations reducing the possibility for superheating of the droplet interior. Blends of near equal concentrations by volume proved to exhibit the most favorable combustion characteristics. Bu40 exhibited the most violent microexplosions of all mixtures studied.

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