Biodiesel refers to a liquid fuel that can replace petrochemical diesel, produced through a process called transesterification using raw materials such as animal and vegetable oils, microbial oils, and waste cooking oil. It exhibits excellent solubility with diesel and can be used either blended or alone with standard diesel fuel. It is a typical clean and renewable "green energy" and an ideal alternative to non-renewable resources like petroleum.
Untreated vegetable oil can also burn in diesel engines, but its viscosity is almost 20 times higher than diesel, with a very high flash point (above 200°C). These characteristics make it difficult for vegetable oil to evaporate inside the diesel engine, causing various issues. After processing, such as esterification processing, vegetable oil is converted into biodiesel, with its fuel properties closely resembling diesel.
Biodiesel is a mixture derived from animal and vegetable fats, mainly consisting of five fatty acid methyl esters: methyl palmitate (C16H32O2), methyl stearate (C18H36O2), methyl oleate (C19H36O2), methyl linoleate (C19H34O2), and methyl linolenate (C19H32O2).
These methyl esters have similar chemical structures, with a methyl ester functional group attached to a carbon chain. Such a chemical composition is much simpler compared to petrochemical diesel, and it is free of aromatic hydrocarbons and mostly sulfur-free. Burning biodiesel in diesel engines significantly reduces emissions of polycyclic aromatic hydrocarbons (PAHs), while emissions of sulfur dioxide (SO2) are almost zero.
In summary, there are two advantages to burning biodiesel: firstly, its physical and chemical properties are similar to traditional diesel, and secondly, burning biodiesel can reduce emissions of certain pollutants such as PM, CO, and HC from diesel engines.