A comprehensive review on the properties of nanofluid fuel and its additive effects to compression ignition engines

Abstract

Nanoparticles (NPs) can be stably suspended in liquid fuels, which was named nanofluid. The stability of the NPs in the fuel is related to whether the pH of the fuel and the diameter of the NPs. Nanofluid fuel was inherently different from slurry fuels. NPs have different effects on the droplets evaporation; meanwhile, NPs exhibit different properties at different temperatures. In the case of related low ambient temperature, NPs have some inhibitory effects on the evaporation behavior of fuel. However, when the ambient temperature reaches a high value, the effects exhibited by NPs would be completely different from those at lower temperatures. The occurrence of these phenomena is related to the difference in the aggregation mode. At low temperatures, NPs would accumulate at the droplets edge, then gasify surrounding fuel, finally form gas bends; and thus the heat transfer process would be reduced. At high temperatures, the heterogeneous agglomerates of NPs are produced, which could lead to micro-explosions. More important is that NPs make positive effects on combustion progress. Metal NPs and metal oxide NPs are able to decrease the oxidation temperature and enhance the cetane number of fuel, which improves the ignition features and increases the evaporation of fuel droplets. These reactions result in the enhancement of combustion process, the significant reduction of engine emissions and heat release rates. It is explicit that nano-additives could dramatically enhance the performance of diesel engines. On the other hand, the mixing of carbon nanotubes with oil could heighten the engine’s performance and improve the engine’s braking efficiency. Furthermore, NPs could effectively reduce emissions, such as carbon monoxide, nitrogen oxides and hydrocarbons.