Disruption and microexplosion mechanisms of burning alcohol droplets with the addition of nanoparticles

Microexplosions of burning liquid fuels have been actively investigated and considered due to the advantage for substantially increasing the overall burning rate. This study concerns possible control of microexplosion occurrence by adding nanoparticles in alcohol fuel without effects of surfactant and ignitable particles as usually seen in the literature. In addition, the essential characteristics and differences between various particles on combustion are discussed. Specifically, we have added three types of ceramic nanoparticles into butanol and isopropanol droplets under different convection environments, i.e., forced convection and natural convection in normal gravity, and free convection in microgravity. A suspended droplet method was performed under convection-free and natural convective conditions while a freefalling droplet method provided a forced convection environment. It was observed that the combustion characteristics of droplets changed from extinction to burnout or from burnout to microexplosion by using different base fuels, by increasing the intensity of flow convection, or by using different kinds of nanoparticles. During combustion, droplets would deform due to the presence of gelation in the outer layer when Al 2 O 3 or SiO 2 nanoparticles were added, but not for TiO 2 . This yielded one of the key factors leading to microexplosions, in addition to the amount of heat absorption during the burning. For the latter, specifically, microexplosions happened when butanol/SiO 2 droplets were tested, but not for butanol/Al 2 O 3 droplets. By comparing the infrared absorptivity of Al 2 O 3 and SiO 2 , distinct amount of absorbed infrared radiation was demonstrated. Such a difference in heat absorption was also key to the creation of microexplosion. As a consequence, microexplosions could be generated when nanoparticles were added into the fuel and formed gelation on the droplet surface, which trapped bubbles in the droplet, while sufficient heat was absorbed by the particles during the burning. The resulted consumption rate had increased by 46% compared to that of pure fuel.& COPY; 2023 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates the control of microexplosion occurrence by adding nanoparticles in alcohol fuel, without the usual effects of surfactant and ignitable particles. The study discusses the essential characteristics and differences between different particles on combustion. The addition of nanoparticles causes deformation of droplets and differences in heat absorption, which are key factors in microexplosion formation.