Internal Boiling to Flame Flickering Insights into Various Spatio temporal Dynamics of Nanofuel Droplet Combustion

Abstract

Addition of metal and metalloid particles (micron and sub-micron) to conventional fuels like Jet-A has been a liquid-fuel extender technique i.e. increased specific energy for less amount of liquid fuels. One of the main advantages of metallic nanoparticles (Aluminium, Iron, and Boron, etc.) is the increased attainable combustion specific energy due to reduced temperatures of metal combustion. Furthermore, nanoparticles of metallic oxides, like cerium oxide, help in the reduction of soot emissions and pollutants like carbon monoxide and NOx because of their oxygen-carrying ability and their capability to oxidize soot particles in their precursor stage. Nanofuel droplets (conventional fuel +nanoparticles) show remarkable instabilities like internal boiling which lead to enhanced atomization of the droplets further leading to flame heat release augmentation. The research work is primarily focused the nanofuel droplet combustion; pathways of secondary atomization, flame dynamics, and the causality between the droplet shape and flame heat release. Here, the possible mechanisms responsible for internal boiling characteristics and its definitive effect on volumetric oscillations, shape deformations of droplets, and average flame heat release are articulated holistically under one umbrella. Being a multiphase system, nanofuel droplets exhibit heterogeneous nucleation leading to formation of vapor bubble mushrooms. These vapor bubbles further grow and eject from droplet free surface thereby opening a new pathway of parent droplet secondary atomization. Continuous disintegration of nanofuel droplets ensures homogeneous air-fuel mixture leading to increased combustion efficiency. Using time-resolved optical diagnostic techniques (High-speed PIV, High-speed shadow imaging, Chemiluminescence Imaging) the droplet shape and flame heat release coupling is investigated. The first part of the work encompasses the combustion dynamics for both low and high-vapour pressure nanofuel droplets in pendant mode where the droplet...