Why measure the vapor pressure of petroleum products?

Why Measure the Vapor Pressure of Petroleum Products?

The vapor pressure of oil is one of the important indicators that indicate the evaporation performance, start-up performance, tendency of generating vapor resistance, and the amount of light distillate lost during storage.

1. To Judge the volatility of oil

The greater the saturated vapor pressure of the oil, the greater the volatility, the more low-molecular hydrocarbons it contains, the easier it is to vaporize, and the more uniform it mixes with air. In this way, the more the combustion of the mixed gas entering the cylinder is to ensure the smooth operation of the engine; at the same time, the wear of parts is reduced, and the fuel consumption is reduced.

2. To determine whether the oil has a tendency to form air resistance during use

The more light components of gasoline, the better the evaporation is. But if the vapor pressure is too high, the gasoline will vaporize in the pipeline, forming a vapor block, and interrupting the fuel supply. On the contrary, if the vapor pressure is too low, the evaporation performance is poor, the combustion is too late to vaporize, and the combustion is incomplete, which will increase the consumption of gasoline.

The greater the saturated vapor pressure of the oil, the greater the tendency to form air lock when used in an engine. When the vapor pressure of automobile gasoline exceeds the specified value, it is easy to form air resistance in the oil pipeline, which will cause the engine to fail to work normally due to the lack of oil.

When used in an internal combustion engine, excessively high vapor pressure is likely to form air resistance in the fuel supply pipeline, causing insufficient fuel supply or interruption, which will cause the engine's power to drop or even stop running. Therefore, both motor gasoline and aviation kerosene have their own restrictions.

3. To Judge the loss during storage and transportation of oil products

The more light components the oil contains, the higher its saturated vapor pressure, and the greater the evaporation loss during storage, transportation and use.

When storing, filling and transporting gasoline, there will always be losses of light fractions. The degree of loss of light fractions can be judged according to the saturated vapor pressure of gasoline. The greater the vapor pressure of gasoline, the greater the evaporation loss during storage. This not only causes large losses, but also pollutes the environment, and increases the risk of fire.

4. To judge the start-up performance of oil products

Too low vapor pressure will affect the starting performance of the oil and reduce the light components with good combustion performance. Therefore, the requirements for vapor pressure are stipulated according to different seasons (for example, the gasoline standard separately stipulates the vapor pressure index in winter and summer).

ASTM D323

experimental method:

Fill the cooled sample into the gasoline chamber of the vapor pressure tester------>connect the gasoline chamber with the air chamber at 37.8°C. Put the tester in a constant temperature bath------>periodically oscillate until the pressure of the pressure gauge installed on the tester is constant------>the pressure gauge reading is corrected to be the Reid vapor pressure.