Key Difference: Diesel is a liquid fuel that is used in diesel engines. It is commonly derived from crude oil. Petroleum diesel or petrodiesel is produced by distilling crude oil between 200 °C (392 °F) and 350 °C (662 °F) at atmospheric pressure. Biodiesel is a fuel developed from vegetable oil or animal fat and works in a diesel engine. These fuels are made as greener and cleaner alternatives to petrol and diesel. Biodiesel is composed of long-chain alkyl (methyl, ethyl, or propyl) esters. It is made by combining chemically reacting with an alcohol producing fatty acid esters.

The process of creating diesel includes drilling for crude oil. The oil drilled from the ground is then sent to a refiner. At the refinery, heat is used to separate out different products at boiling points. The oil is then sent through a distillation process where it is applied with heat and pressure causing a chemical reaction. The application of heat and pressure determines if the product becomes petrol or diesel. Following distillation, the fuel is blended with additives that help improve the quality of the fuel. The crude oil is composed of various hydrocarbons that differ in composition. These different hydrocarbons are what make the different products that are derived from the oil. Simple hydrocarbons such as CH4, C2H6, C3H8, and C4H10 are light gases and are used in solvents for paints. The other longer chains of hydrocarbons are used to create fuel.

Diesel is a liquid fuel that is used in diesel engines. It is commonly derived from crude oil, but there are also alternatives that are not derived from distilling petroleum fuel oil; these are known as biodiesel, biomass to liquid (BTL) diesel and gas to liquid (GTL) diesel. The name of the fuel is derived from the name of German inventor Rudolf Diesel who created the compression-ignition engine. Petroleum diesel or petrodiesel is produced by distilling crude oil between 200 °C (392 °F) and 350 °C (662 °F) at atmospheric pressure. Diesel has a mix of carbon chains between 8 and 21 carbon atoms per molecule. Diesel fuel quality is measured by its Cetane number. A higher cetane number indicates that the fuel ignites more readily when sprayed into hot compressed air. Diesel has a disadvantage in the winter as a vehicle fuel because of its viscosity (ability to flow). The viscosity of diesel increases as the temperature decreases and the fuel requires a special fuel pump for pumping the fuel.

Diesel has approximately 34.6 MJ/liter of energy content and produces 2.65 kg of CO2 per kilo of diesel used. It has a calorific value of 45.5 MJ/kg (megajoules per kilogram) and has a boiling range of 250°C to 350°C. Diesel is a popular alternative to petrol because of its ability to provide a better fuel economy and has less CO2 emissions. Diesel is a popular source of fuel and is believed to be better for cars that have a high consumption. It is also significant cheaper compared to petrol and provides more torque at low speeds.

Biodiesel is a fuel developed from vegetable oil or animal fat and works in a diesel engine. These fuels are made as greener and cleaner alternatives to petrol and diesel. Biodiesel is composed of long-chain alkyl (methyl, ethyl, or propyl) esters. It is made by combining chemically reacting with an alcohol producing fatty acid esters. Biodiesel is made in a way that it can be used in petrodiesel engines. They can be used pure or as 100% biodiesel or can be combined in different percentages with petrodiesel. 100% biodiesel may require making minor modifications to the engine to avoid maintenance and performance problems. There are four different blends that are commonly used: B100, B20, B5 and B2. B100 is 100% biodiesel, B20 is 20% biodiesel with 80% petrodiesel, B5 has 5% biodiesel and 95% petrodiesel and B2 has 2% biodiesel and 98% petrodiesel. Many auto manufacturing companies have started providing diesel cars that allow up to B20 limits.

Biodiesel has different solvent properties than petrodiesel and can degrade natural rubber gaskets and hoses at a faster rate. There is an alternative FKM material that is nonreactive to biodiesel. In addition to cars, biodiesel is also being employed in railways, aircrafts and as heating oil. Biodiesel can also be used to clean up oil spills because of its ability to significantly dissolve crude oil, depending on the source of the fatty acids. Biodiesel concept was introduced by scientists E. Duffy and J. Patrick in 1853. Biodiesel is a cleaner alternative to diesel as it has significantly less emissions and is completely renewable.

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