Differences between biodiesel and conventional diesel

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1. Definitions of biodiesel and conventional diesel: Biodiesel refers to a renewable diesel fuel that can replace petrochemical diesel; it is produced through an esterification process using oils from oil crops, wild oil plants, aquatic microalgae, as well as animal fats and oils from food waste. It is a monoalkyl ester of a long-chain fatty acid obtained through techniques such as thermal pyrolysis of biomass. Biodiesel itself is a mixture of complex organic compounds with a very high oxygen content. Diesel: Also known as oil residue, it is a type of oil product obtained from the refining of petroleum. It is composed of a mixture of different hydrocarbons. Its main components are alkanes, cycloalkanes, or aromatics with 9 to 18 carbon atoms. Its chemical and physical properties lie between those of gasoline and heavy oil; its boiling point ranges from 170°C to 390°C, and its specific gravity is 0.82–0.845 kg/l. 2. Main difference: Energy classification – The calorific value of ordinary diesel is 35.5 MJ/L, with a cetane number of 50 (standard) ； The calorific value of biodiesel ranges from 32.4 to 36.7 MJ/L, and its cetane number is between 5 and 70. Although biodiesel has a slightly lower calorific value, it has a high cetane number. Moreover, the oxygen-containing components in biodiesel ensure more complete combustion when mixed with conventional diesel, resulting in higher thermal efficiency. Therefore, using them together yields good performance, allows for maximum utilization of the diesel’s power, and provides excellent overload characteristics. Environmental pollution: Compared to conventional diesel, vehicles using biodiesel emit only 10% of the toxic organic compounds found in exhaust gases, and only 20% of particulate matter. Carbon monoxide emissions can be reduced by 95% when a catalyst is used, and there are no emissions of toxic substances such as sulfur dioxide or lead. Properties: The properties of biodiesel are very similar to those of conventional diesel. The kinematic viscosity of conventional diesel is 3–8, while that of biodiesel is 5–10. It can be used alone or blended with diesel in any proportion, without requiring any modifications to the engine or fuel system. Apart from a slight reduction in power when used alone, blends at concentrations below 50% show no difference from conventional diesel in terms of performance. In terms of mechanical damage, it causes no corrosion to the engine or fuel system, no coking in the injectors, and no carbon buildup in the combustion chamber. It has excellent lubricating properties, which reduces the wear rate of the fuel injection pump, engine cylinder block, and connecting rods. Safety: Due to its high flash point, biodiesel is not considered a hazardous material, making it relatively safe to store, transport, and use. Compared to conventional diesel, biodiesel possesses the following unparalleled advantages: 3. Can biodiesel be used as a fuel on its own? As the editor has learned, in China, biodiesel is always used in combination with petrochemical diesel in a certain proportion. This approach helps to reduce fuel consumption, improve performance, and decrease exhaust pollution. The excellent properties of biodiesel ensure that the exhaust emission standards for engines using biodiesel not only meet the current European Standard II, but also satisfy the even stricter European Standard III, which is set to be implemented in Europe soon. Furthermore, since the carbon dioxide emitted during the combustion of biodiesel is much lower than the amount absorbed by the plants during their growth, this helps to address global warming, a serious environmental problem that poses a threat to humanity due to carbon dioxide emissions. In summary, there are indeed some drawbacks to using biodiesel directly as a fuel for diesel engines, as it has an impact on the engine. Biodiesel has a higher density and surface tension than conventional diesel, its fractions are heavier and narrower with higher volatility, and its viscosity is also greater than that of conventional diesel. The viscosity of biodiesel is generally 3.5–5.0 mm2/s, which is about 15% to 75% higher than that of conventional diesel, whose viscosity is 2.0–3.5 mm2/s. Therefore, larger droplets will be formed when the fuel nozzle atomizes, which deteriorates the atomization. Therefore, the use of biodiesel makes incomplete combustion more likely to occur; currently it is recommended to use it in combination with petrochemical diesel. However, as technology advances, it is not impossible for biodiesel to be used in its pure form in the future.