Turning biodiesel glycerol into oxygenated fuel additives and their effects on the behavior of internal combustion engines: A comprehensive systematic review

The boom of the biodiesel industry has ramped up global glycerol production. Unfortunately, a large portion of the glycerol generated by this growing industry is recklessly discharged into the environment, overshadowing the environmental benefits of biodiesel fuel. Glycerol can be a valuable chemical platform in various processes to produce a wide spectrum of chemicals and fuels. A promising application pathway is to return glycerol to the fuel cycle by converting it into fuels or additives. The energy content of glycerol can then be effectively recovered while the harmful exhaust emissions of combustion engines can be substantially mitigated. This paper offers a broader review of the state-of-the-art advances in using glycerol and its derivatives to improve the operation of internal combustion (IC) engines. Various routes developed to convert glycerol into oxygenated fuel additives are first introduced. The effects of glycerol and its derivatives on the behavior of IC engines are then comprehensively summarized and mechanistically discussed. The pros and cons of using glycerol and its derivatives in diesel/gasoline fuel formulations are examined to highlight important future research directions in this domain. Overall, the straight or emulsified use of glycerol in IC engines is not recommended because of several challenging technical and environmental issues. Nevertheless, incorporating well-elaborated glycerol derivatives into diesel and gasoline fuels can improve engine performance while potentially lowering hazardous exhaust emissions. Future investigations should focus on manufacturing and examining new glycerol derivatives to enhance the performance of IC engines while meeting stringent emission norms.