Nanoparticle additive fuels: Atomization, combustion and fuel characteristics

Nanoparticle additive fuels (NAFs) are new generation fuels containing nano-sized functional agents that regulate combustion, atomization, and emission behavior without causing a substantial change in the fluid characteristics of the base fuel. These promising agents for the conservation of limited reserves, reducing energy consumption and pollution, also pave the way for the production of new fuels or the adaptation of conventional fuels to specific operating conditions, even at dilute concentrations. Even so, the combustion kinetics of NAFs with dual-phase structures are different and complex from solid fuels and non-additive liquid fuels. This review highlights the unique potential of NAFs and explains their combustion mechanism. The primary atomization of NAFs sprayed from injection systems is studied. Then, the results of droplet scale tests presented in the literature in recent years are examined and the disruption (atomization), combustion and evaporation behaviors of NAFs are determined. In addition, experimental and numerical evaluations of the combustion of nanoparticles (NPs) in individual and aggregate forms are performed in order to better understand the effect of the size and concentration of used NPs on combustion. The effects of NPs on the performance and emission values of liquid fuels used in public spaces and propulsion systems are determined by evaluating the intermittent and continuous combustion laboratory test results of NAFs. The results showed that the presence of NPs has profound effects on the combustion physics and combustion chemistry of hydrocarbon fuels. While the size and concentration of NPs are responsible for the physics of combustion, the components, catalytic activity, oxygen content, reactivity and calorific value of the NPs are responsible for the combustion chemistry. Spray characteristic tests showed that the optimum NP concentration for NAFs was 0.5 wt%, while the tests on the droplet scale for evaporation and combustion characteristics showed that the optimum particle concentration was 2.0–2.5 wt%. In the tests made for engine performance and emission values, such a result could not be drawn because the critical concentration differs for the dependent variables. However, it has been observed that NPs (Al, B, Fe, Al₂O₃, Fe₂O₃, CeO₂, ZnO, graphene oxide, etc.) with high calorific value, thermal conductivity, and catalytic activity have significant effects on these parameters.