1、Properties

（1）Appearance: tea yellow or dark brown with blue surface, characteristic odor, few bubbles generated when shaken, which disappear quickly, feeling smooth, giving a sense of oil, slow volatility;

 （2）Required properties: chiefly evaporability, flammability, stability, safety, cold flow

①Evaporability: Diesel is burnt in gaseous state in the cylinder. It must be evaporated and form combustible mixed gas with air before enabling the engine to start and work as designed, therefore, the diesel shall be of good evaporability. However, its evaporability shall not be too strong, because too fast evaporation will lead to buildup of much diesel when it burns, which makes the engine work unstably. Meanwhile, strong evaporability means light distillates and inevitably low viscosity, which makes not only more abrasion of the fuel injector , but also the atomization quality decrease, worsening combustion process.

②capability of diesel oil. The temperature at which diesel oil will ignite by itself when there’s no source of ignition is called self-ignition point, which affects engine performance directly. The cetane number (CN) of diesel oil is a measure of its flammability. With the higher CN, the performance of combustion is better.

③Stability: The stability of diesel oil affects the engine just like gasoline, indicating its propensity to form gums and sediments during storage and transport.  Poor stability can result in degradation, a darkening in color, and increase in sediments and gums as a result of oxidation, plugging the filter. Degradation by oxidation can lead to buildup of a great deal of carbon, paint film formation at the injection system, and sticking and wear of the piston ring, which has a considerable impact on the storage and use of the diesel fuel.

④Safety: Flash point not only controls evaporability but also ensures safety of the diesel. The safety of the diesel oil increases with rise of flash point. Normally a flash point above 35℃ is considered safe for handling and storage of light fuel.

⑤Cold flow: solidifying point and Cold Filter Plugging Point (CFPP) are two major indicators of cold flow performance of the diesel fuel. Diesel is classified into a range of grades by solidifying point in China. Solidifying point, the highest temperature at which diesel will not flow, indicates the boundary temperature for storage, transport and loading/unloading activities. Generally speaking, solidifying point of diesel fuel is 5-10℃ lower than the ambient temperature. CFPP is the highest temperature at which the fuel can not pass through a standard test filter under given conditions. There is a congruent relationship between solidifying point and performance of diesel fuel, and that’s why the scope of actual application temperature for individual grades of diesel oil is classified by the solidifying point. For the same diesel, CFPP is 4~6 ℃ higher than solidifying point.

2、Diesel Grades

（1）Light diesel (GB252－2000): 10#, 5#, 0#, -10#, -20#, -35#, -50#;

（2）Vehicle fuel（GB/T19147－2003）: 10#, 5#, 0#, -10#, -20#, -35#, -50#;

In China, the diesel grades are designated on the solidifying point basis, for instance, the solidifying point of 0# diesel shall be no higher than 0℃.

3、Selection

Selection of diesel oil shall depend on the ambient temperature. There is no congruent relationship between the ambient temperature and the diesel grade, that is, for the temperature 0℃, not 0# but 10# diesel shall be selected, because for 0# diesel, when the gauge reads 0℃, the diesel has stopped flowing. Therefore, when the temperature is 0℃, the diesel will not work if 0# is selected. Proper selection of diesel oil shall be made according to the following principle: the solidifying point selected shall normally be 5－7℃ lower than the environment temperature with CFPP slightly lower than the ambient temperature. Selection of diesel grades can be made as follows.

10# light diesel- applicable to a diesel engine with preheating device.

5# light diesel- applicable to a region with 10% risk rate of the lowest temperature above 8℃;

0# light diesel- applicable to a region with 10% risk rate of the lowest temperature above 4℃;

-10# light diesel- applicable to a region with 10% risk rate of the lowest temperature above -5℃;

-20# light diesel- applicable to a region with10% risk rate of the lowest temperature above -14℃;

-35# light diesel- applicable to a region with 10% risk rate of the lowest temperature above -29℃;

-20# light diesel- applicable to a region with10% risk rate of the lowest temperature above -44℃;

The lowest temperature with 10% risk indicates that the probability of the lowest temperature being lower than this temperature is 0.1.