一、 The relationship between viscosity and diesel quality

Viscosity has a close relationship with the size of the diesel engine fuel supply and the quality of atomization. If the viscosity of diesel oil is too small, it is easy to leak from the gap between the plunger and the pump barrel of the high-pressure oil pump, which will reduce the fuel injected into the cylinder and cause the engine power to drop. The smaller the viscosity of diesel oil, the smaller the diameter of the droplets after atomization, and the shorter the range of the sprayed oil flow, so it cannot be evenly mixed with all the air in the cylinder, resulting in incomplete combustion. At the same time, the oil pump of the diesel engine is lubricated by diesel oil. If the viscosity is too small, it cannot play a lubricating role. The viscosity of diesel oil is too large, which will cause difficulty in supplying oil. At the same time, the diameter of the sprayed oil droplets is too large and the oil flow is too long, which reduces the effective evaporation area of ​​the oil droplets and slows down the evaporation speed, which will also make the mixture gas. Uneven composition, incomplete combustion, and increased fuel consumption. Therefore, diesel needs a suitable viscosity range.

二、The quality assessment of diesel

Viscosity is divided into dynamic viscosity and kinematic viscosity. The viscosity analysis of automotive diesel is mainly evaluated by kinematic viscosity. The measurement of diesel kinematic viscosity is carried out in accordance with GB/T 265-88 "Determination of Kinematic Viscosity of Petroleum Products and Calculation of Dynamic Viscosity". The main instrument is a glass capillary viscometer, which is suitable for liquid petroleum products belonging to Newtonian fluids.

The formula for its kinematic viscosity is as follows:

νt=Cτt

In the formula νt----at the temperature t, the kinematic viscosity of the sample, mm2/s;

τt----at the temperature t, the average flow time of the sample, s

C----capillary viscometer constant, ㎡/s2

    From the above formula, we can see that the temperature has a great influence on the viscosity, so using a temperature control device with better temperature control accuracy is effective for the accuracy of the experimental results.

Secondly, different capillary viscometers have different constant C values. The measurement method is as follows: use a known viscosity to measure the time it passes through the capillary viscometer under specified conditions, and then calculate C according to the formula. Note that the viscosity of the selected standard liquid should be close to that of the sample to reduce errors. Usually, different specifications of viscometers are given the calibration value of C when they leave the factory, but because the quality of the capillary produced by each manufacturer is uneven, it is very important to choose a capillary.