Oxidation Stability Test of Distillate Fuel Oil

1. Overview of Test Samples

Distillate fuel oil is a middle distillate produced from petroleum refining, including common power fuels such as diesel and kerosene, which is widely applied to vehicles, ships, construction machinery and generator sets. During long-term storage and service, fuel oil is prone to oxidation reaction with oxygen, generating insoluble substances like gum and sediments. Such substances will cause oil circuit blockage, engine wear and oil deterioration, directly affecting the service life and operation safety of power equipment. Therefore, oxidation stability testing shall be conducted before oil delivery, warehousing and use to evaluate the inherent storage stability of the oil product.

2. Test Purpose and Executive Standard

The accelerated oxidation method is adopted to simulate the long-term oxidation and aging process of oil products, quantitatively measure the content of insoluble substances generated after distillate fuel oil oxidation, and assess the inherent stability of the oil. Fuel oil with unqualified oxidation stability is highly likely to deteriorate in a short period, producing impurities that corrode the fuel supply system and reduce combustion efficiency. Standardized testing helps screen qualified oil products and avoid equipment failure risks.

The test strictly complies with the industry standard SH/T 0175 Determination of Oxidation Stability of Distillate Fuel Oil (Accelerated Method). The supporting test equipment is the SH0175 Distillate Fuel Oil Oxidation Stability Tester independently developed by Shandong Shengtai Instrument Co., Ltd. The overall structure, temperature control system and ventilation system of the instrument fully meet the standard requirements, enabling 4-channel synchronous fully automatic accelerated oxidation testing.

3. Experimental Preparation

1. Test sample: Filtered distillate fuel oil sample to be tested
2. Experimental instruments and consumables
   • 1 unit of SH0175 distillate fuel oil oxidation stability tester mainframe
   • Matching light-proof dark box, 4 sets of oxidation test tubes, condenser tubes and oxygen supply glass tubes
   • Flexible hose with inner diameter of φ6, 50~100℃ glass thermometer
   • Industrial oxygen cylinder with purity ≥99.5%, pressure stabilizing valve and filtration device
   • Pure water circulating water supply system, cleaning and wiping consumables

4. Test Operation Procedures

1. Pre-inspection of the instrument: Confirm the reliable grounding of the equipment shell, and verify the intact functions of the temperature control meter, flowmeter and timer. Install a filter and pressure stabilizing valve at the front end of the oxygen cylinder, and connect it to the air inlet on the side of the instrument.
2. Pre-connection of water and gas supply: Connect the water inlet and outlet of the condenser tube to the water circuit interfaces of the instrument with hoses respectively, and connect external circulating cooling water; dock the oxygen supply hose with the air outlet of the flowmeter and the glass oxygen supply tube.
3. Temperature rise setting of the equipment: Connect the 220V/50Hz power supply, turn on the mainframe switch, and set the standard test temperature at 95℃ on the temperature controller. If the temperature control accuracy is insufficient, long press the temperature rise key to activate the self-tuning function, and wait for the water bath to stabilize at 95℃±0.2℃.
4. Sample loading and light-proof storage: Fill a clean oxidation test tube with 350ml±5ml of filtered oil sample, and place it in the light-proof dark box for temporary storage for no more than 1 hour. After the water bath temperature stabilizes, insert the test tube into the test hole of the instrument, and assemble the condenser tube and oxygen supply pipeline in sequence.
5. Oxygen flow adjustment: Turn on the oxygen source, adjust the flowmeter valve, and stably control the oxygen flow of each single oxidation tube at 50ml±5ml.
6. Timing and test initiation: Set the test duration specified in the standard. After all samples are in position, press the timing switch. The instrument will count time automatically, and trigger an automatic sound and light alarm when the set duration expires.
7. Sampling, cooling and finishing: After the alarm, take out the oxidation test tubes in turn, place them in the light-proof dark box to cool to room temperature, and then proceed to the determination of insoluble substance content. After the test, close the oxygen valve and cut off the equipment power supply in time, and clean the glassware and instrument table.

5. Experimental Data and Result Evaluation

Multiple groups of parallel tests on distillate fuel oil were carried out with the SH0175 oxidation stability tester. The equipment has a temperature control accuracy of up to ±0.1℃, stable and controllable oxygen flow, and good parallelism of 4-channel synchronous detection data.

The actual sample loading volumes of the four groups of parallel samples are 348mL, 351mL, 349mL and 352mL respectively, all meeting the standard requirements. After 16 hours of accelerated oxidation test on the same batch of 0# diesel, the insoluble substance test values of the four samples are 0.68, 0.72, 0.65 and 0.70mg/100mL respectively. All samples are judged qualified against the standard limit of 2.0mg/100mL, with an average value of 0.6875mg/100mL, a range of 0.07mg/100mL, and a relative deviation of less than 5%, showing excellent parallel repeatability.

The overall power of the instrument is ≤3600W, and the timing error is ≤±1s. The matching light-proof dark box avoids the interference of light on the oxidation reaction, and the instrument supports temperature calibration, with no obvious systematic deviation in test data.