Nanofuel Droplet Evaporation Processes

Abstract

The concern about the level of toxic emissions from the use of
fossil fuels in internal combustion engines is widely held. Several alternatives
have been suggested to mitigate this concern including the use
of biofuels in the engines, hybrid internal combustion–electric power
systems and electric propulsion systems. In the last decade there has
been progress with adding nano-sized particle additives to hydrocarbon
fuels with the aim of improving the thermo-physical properties. The
nano-sized metallic particles increase the surface-to-volume ratio of the
resultant nanofuel suspensions. Reductions in the emissions levels from
the combustion of these nanofuels have been reported; these improvements
derive from the reductions in ignition delay, and therefore, higher
burning rates arising from increases in the evaporation rates of the fuel
droplets. Thus, droplet evaporation mechanisms influence the ignition
time of the droplets, and consequently the ignition delay time. Optimizing
these parameters can help to reduce the emissions from the internal
combustion engines. The study presented here examines the up-to-date
results of work carried out by various researchers on the droplet evaporation
mechanisms of nanofuel droplets. The predominant processes
presented as being responsible for the enhancement of the droplet
evaporation rate are that the nanoparticle additives increase the droplet
fuel temperature by radiative absorption, and that at high temperature
values the agglomerates of the nanoparticles heat up residuals of the liquid
fuel causing fuel droplet disruptions and micro-explosions. The various
parameters that affect these and other nanofuel droplet evaporation
mechanisms are presented. A case is made for further studies in this
area.