Test Method for Flash Point of Diesel Oil

Test Method for Flash Point of Diesel Oil

Diesel oil is a light petroleum product mainly composed of complex hydrocarbon mixtures with carbon atoms ranging from about 10 to 22, and it serves as a dedicated fuel for diesel engines. It is produced by processes such as crude oil distillation, catalytic cracking and hydrocracking, and can also be obtained from shale oil processing or coal liquefaction.

Diesel oil is divided into two main categories: light diesel oil with a boiling point range of approximately 180～370℃, and heavy diesel oil with a boiling point range of about 350～410℃. Light diesel oil is commonly available at gas stations and widely used in the power systems of large vehicles, railway locomotives and ships.

Experimental Purpose

Evaluate fire risk: The lower the flash point, the more volatile diesel oil becomes, the higher the risk of forming flammable mixtures with air, and the greater the possibility of flash fire. Determining the flash point can clarify its safety under normal temperature and high-temperature conditions.

Ensure storage and transportation safety: According to national standards, the closed flash point of vehicle diesel shall be no less than 55℃. As an important basis for classifying the hazard level of flammable liquids, this index directly guides the formulation of fire prevention measures and the specifications for hazardous chemical management.

Detect oil contamination: If light components such as gasoline are mixed into diesel oil, the flash point will decrease significantly. Therefore, an abnormally low flash point may indicate adulteration or deterioration of the oil, which will affect the normal operation of the engine.

Experimental Sample and Instrument

Sample: Diesel oil

Instrument: SH105B Fully Automatic Closed Flash Point Tester, compliant with ASTM D93

Experimental Procedures

1. Sample Preparation

Take about 50 mL of diesel sample and ensure it is free of moisture and impurities. If the sample contains water, dehydrate it with anhydrous sodium sulfate or calcium chloride.Allow the sample to stand to eliminate bubbles and avoid loss of volatile components.

2. Instrument Inspection and Calibration

Adopt a closed flash point tester that meets ASTM D93 requirements (e.g., Teck MINI Flash PM).Calibrate the temperature sensor: verify accuracy with reference materials such as n-hexadecane (flash point: 135℃±2℃).Check the ignition source (flame size: 2~4 mm), stirring speed (90~120 rpm), and the integrity of the sealing gasket.

3. Sample Filling and Initial Setting

Pour the sample into the copper test cup up to the scale line and seal with the lid.Set the initial temperature at least 28℃ lower than the expected flash point to prevent premature vapor generation during preheating.

4. Heating and Ignition Test

Heat the sample at a rate of 5~6℃ per minute.With every 1℃ temperature rise, the stirring is automatically stopped, and the ignition source is introduced to sweep over the vapor space to observe flash ignition.When the temperature is 5℃ close to the expected flash point, reduce the heating rate to 0.5~1℃/min to improve test accuracy.

5. Environmental Control

Maintain the laboratory temperature at 15~35℃ and relative humidity ≤ 85%.Avoid air flow interference to prevent vapor concentration fluctuation from affecting test results.If the instrument is not equipped with automatic atmospheric pressure correction, manual correction is required: the flash point shall be corrected by approximately ±0.2~0.3℃ for every ±1 kPa atmospheric pressure change.

6. Test Completion and Cleaning

After the test, clean the test cup only after it cools down to room temperature to prevent deformation and avoid affecting subsequent tests.

Experimental Results

The repeatability and reproducibility of test results fully meet the error tolerance requirements of GB 261 standard. The test data is stable and accurate, which can satisfy routine testing and quality control requirements for closed flash point of diesel oil, various fuel oils and lubricating oils.