As we all know, the structure of diesel engines and gasoline engines is not the same. The main difference between a diesel engine and a gasoline engine is that the ignition method is different; the diesel engine is mainly a compression-ignition type, while the gasoline engine is an ignition type and includes a spark plug in its structure. Additionally, the compression ratios of the two fuels differ, with the diesel engine having a compression ratio of 16-20:1, which is higher than the 8-10:1 of the gasoline engine. It is precisely because of these differences that the internal environments of the two during operation are also different. Firstly, the operation of the gasoline engine, ignited by the spark plug, is short, fast, and produces less noise; the internal heat load is relatively small. In contrast, the heat load of the diesel engine is larger than that of the gasoline engine, with higher internal temperatures and pressures. This causes the lubricating oil to oxidise and deteriorate more easily and generates more NOx and particulate matter. Furthermore, the fuel used in the diesel engine is diesel, while the gasoline engine uses gasoline. Generally, the sulphur content of diesel is relatively higher, making it more prone to cause engine corrosion.

As a result, the requirements for lubricating oil are also different; diesel engine oil must have better high temperature purity, acid neutralisation ability, and thermal oxidation stability than gasoline engine oil, while gasoline engine oil must have better wear resistance and low temperature dispersion than diesel engine oil. Typical diesel engine oil and gasoline engine oil main indicators:

From the above table, it is obvious that the difference between diesel engine oil and gasoline engine oil: the base number is related to the acid neutralisation ability, and the base number of diesel engine oil is generally higher than that of gasoline engine oil, reflecting that the requirements of diesel engine for acid neutralisation ability are higher than that of gasoline engine; The nitrogen content is related to the dispersibility, and the diesel engine oil is much lower than the gasoline engine oil, indicating that the requirements for gasoline engine are higher in terms of sludge dispersion. The calcium content is related to the cleanliness, and the diesel engine oil is higher than the gasoline engine oil, indicating that the cleanliness requirements of the diesel engine are generally higher than that of the gasoline engine.

Phosphorus content and zinc content are related to wear resistance. Gasoline engines, due to their short stroke and fast speed, have higher requirements for anti-wear performance. Additionally, the current inclusion of molybdenum salts in the formula of motor oil is also based on the aim of reducing wear. In diesel engine oil, apart from ZDDP, various other types of antioxidants are added to enhance its antioxidant performance. The differences mentioned above are determined by the characteristics of diesel engine oil and gasoline engine oil. The variations in the types and proportions of additives found in diesel engine oil and gasoline engine oil, combined with the differences in fuel and the distinct structures and working conditions of the two engines, result in different exhaust gases being produced. Consequently, the focus of exhaust treatment also varies; gasoline engine exhaust primarily concerns carbon monoxide (CO) and hydrocarbons (HC), typically managed with a three-way catalytic converter, while diesel engine exhaust mainly addresses nitrogen oxides (NOX) and particulate matter (PM), frequently handled using DPF (particulate filter) and SCR (Selective Catalytic Reduction) technology.

To meet certain standards and specifications, the oil must be verified by the relevant bench test; diesel engine oil and gasoline engine oil are also different in the bench test. Diesel engine oil is mainly for the Caterpillar series of cleanliness test and MARK T series of anti-oxidation and anti-corrosion test, while gasoline engine oil is mainly for CRC L-38 bearing corrosion test and evaluation of oxidation, anti-wear, anti-sludge paint film, energy saving and other performance of MS programme series test.

At present, there is also a type of general lubricating oil for gasoline and diesel on the market; this kind of oil first appeared in the military fleet of Western countries to prevent accidents caused by using the wrong oil. As we have mentioned before, diesel engines and petrol engines have different requirements for oil; if one oil product meets the different requirements of both engines at the same time, the oil formula needs to be carefully adjusted, and its components will be more complex, such as adding a detergent with good thermal stability and ZDDP for compounding, etc. The evaluation is more difficult, the cost is higher, and the demand in the market is relatively small.(Due to the limited level of the author, it is inevitable that there will be mistakes, please correct )