Lubrication is a procedure that involves the use of a chemical called lubricant to reduce wear on surfaces that are in relative motion with each other. It aids in the transmission of pressure created between opposing surfaces. Lubricants serve as anti-friction agents. They allow for flat-level operations by retaining superior machine functionality and reducing the likelihood of recurring breakdowns. In today's world, the price of crude oil is rising in tandem with the depletion of reservoirs (oil). As a result, protecting a pollution-free environment is a major responsibility. The focus of current research is on creating and using an ecologically friendly lubricant made from renewable resources. This paper discusses the preparation, characteristics, characterization advantages, and uses of vegetable oil-based non-edible lubricants. Chemical changes are required since vegetable oil-based lubricants have lower thermal and oxidative stability. The article explores the required chemical modification approaches for improving the properties of bio-lubricants. The characterization of bio-lubricants has been elaborately discussed, highlighting the major pros and cons. The drawbacks and also future scope of the bio-lubricants have been highlighted.

Meeting the emission norms specified by governing bodies is one of the major challenges faced by engine manufacturers, especially without sacrificing engine performance and fuel economy. Several methods and techniques are being used globally to reduce engine emissions. Even though emissions can be reduced, doing so usually entails a deterioration in performance. To address this problem, nanoadditives such as cerium oxide (CeO2) nanoparticles are used to reduce engine emissions while improving engine performance. However, some aspects of the application of these nanoadditives are still unknown. In light of that, three sizes of CeO2 nanoparticles (i.e., 10, 30, and 80 nm) and at a constant volume fraction of 80 ppm were added to a 20% blend of waste cooking oil biodiesel and diesel (B20). A single-cylinder diesel engine operating at a 1500 rpm speed and 180 bar fuel injection pressure was used to compare the performance and emission characteristics of the investigated fuel formulations. The results showed that the addition of CeO2 nanoparticles led to performance improvements by reducing brake specific fuel consumption. Moreover, the catalytic action of CeO2 nanoparticles on the hydrocarbons helped achieve effective combustion and reduce the emission of carbon monoxide, unburnt hydrocarbon, oxides of nitrogen, and soot. Interestingly, the size of the nanoadditive played an instrumental role in the improvements achieved, and the use of 30 nm-sized nanoparticles led to the most favorable performance and the lowest engine emissions. More specifically, the fuel formulation harboring 30 nm nanoceria reduced brake specific fuel consumption by 2.5%, NOx emission by 15.7%, and smoke opacity by 34.7%, compared to the additive-free B20. These findings could shed light on the action mechanism of fuel nanoadditives and are expected to pave the way for future research to develop more promising fuel nanoadditives for commercial applications.