Boron for liquid fuel Engines-A review on synthesis, dispersion stability in liquid fuel, and combustion aspects

Energetic metal or metalloid particles are considered to be potential secondary energy source for energy generation and propulsion. This is mainly due to their higher gravimetric and volumetric heating values compared to that of hydrocarbon fuels. These energetic particles have the capacity to produce a huge amount of heat upon reaction which is very essential for any energy or thrust producing device. Many of these energetic particles may offer a beneficial role in terms of improvement in combustion efficiency and reduction in exhaust emission. Boron is considered to be one of the best suited candidates based on its heating values. However, the full potential of boron particles has not been realized yet in any practical combustion systems. Numerous studies have been carried out on ignition/combustion characteristics of boron particles considering mostly micron-size particles. Recent advancement of nanotechnology has opened up a new avenue for utilizing energetic nanoparticles as fuel additives in liquid fuel combustion systems. Few review articles highlighting mainly the ignition and combustion mechanisms of boron are available in literature; however, recent development on ignition/combustion of boron nanoparticles as well as its application in liquid fuel engines is not yet reviewed comprehensively. The present paper encompasses the present status and underlying challenges in synthesis process of boron nanoparticles, dispersion and stability of boron nanoparticles in liquid hydrocarbon fuels, effect of surfactant or surface modification on dispersion stability, ignition and combustion characteristics of boron loaded liquid fuel as well as particle combustion, understanding the positive thermal contribution from boron particles burning, and characterization of post-combustion products in terms of chemical and physical properties.