Determination of the freezing point of engine coolant

Determination of the freezing point of engine coolant
Overview
  Engine coolant, also known as antifreeze, is mainly used in the cooling system of automotive engines. It serves the functions of heat dissipation and cooling, corrosion prevention and rust prevention, and freezing protection. It is prepared by blending the base fluid with corrosion inhibitors. It is divided into original liquid and concentrated liquid. In low-temperature environments, if the coolant freezes, the volume expansion will rupture the water tank and pipelines, causing damage to the engine cooling system. Therefore, the freezing point is a key indicator for evaluating the low-temperature freezing protection performance of the coolant.

Experimental purpose
  To determine the freezing point of engine coolant and its concentrated liquid, to evaluate the coolant's low-temperature antifreeze ability, and to determine whether the product is qualified. This test is carried out in accordance with SH/T0090 "Method for Determining the Freezing Point of Engine Coolant". The SH128 automatic freezing point tester is developed and manufactured based on this industry standard and is used to complete the automatic freezing point detection of the coolant.

Experimental samples and instruments

Experimental samples: Engine coolant (or its concentrated liquid)
Experimental instruments:
1. SH128 automatic freezing point tester
2. Graduated cylinder, cooling tube, matching sensors, rubber stoppers, and other auxiliary accessories

Operation steps
1. Use a graduated cylinder to measure 75-100 mL of the sample coolant to be tested, and place it in a clean and dry cooling tube. Put the cooling tube in the cold bath, tighten the bottle cap, adjust the position of the stirrer to ensure that the temperature sensor is in the center of the stirrer circle.
2. Confirm that the alcohol liquid level inside the cold bath is submerged in the refrigeration path and the sample position, the power supply is reliably grounded, and connect a 220V power supply. First, pre-cool the cold bath by 3-5℃, then enter the touch screen operation interface.
3. Enter the parameter setting page, enter the sample number, sample name, and set the expected freezing point and other test parameters. You can calibrate the temperature as needed.
4. Return to the main interface, confirm that the stirring and refrigeration devices are in normal condition, click start, and the instrument automatically runs the test, real-time collects the temperature of the cold bath and the sample, and draws a temperature change curve. After the sample cools and crystallizes, the temperature rises to the highest temperature, which is the freezing point.
5. The test is completed when the instrument beeps. Stop the stirring, automatically output and print the freezing point results; the test data is automatically saved and can be viewed in the historical records or exported to a USB drive for retention.
6. If you need to conduct the next set of tests continuously, the instrument does not need to be shut down; after all the tests are completed, in the system settings interface, turn off the refrigeration device and manually turn on the heating to raise the cold bath to normal temperature.

Data analysis and result evaluation
  According to the SH/T0090 standard definition, the freezing point is the highest temperature reached when the sample cools and crystallizes, and the temperature rises. The SH128 automatic freezing point tester has a temperature display accuracy of 0.1℃, the temperature control range of the cold bath is -70℃ to 30℃, and the entire machine has excellent measurement repeatability, which can meet the laboratory testing requirements for engine coolant and concentrated coolant.

- Sample A, nominal freezing point -25℃, the instrument measured freezing point -25.2℃; the measured value is within the allowable range, the antifreeze performance is qualified, and it can be used normally in -25℃ environment.

- Sample B, nominal freezing point -35℃, the instrument measured freezing point -28.1℃; the measured freezing point is much higher than the product's marked indicators, indicating that the effective antifreeze components of the coolant are insufficient, and it is prone to crystallization and freezing in low-temperature conditions. If it is used in a vehicle, freezing in the low-temperature environment will cause expansion and risk of cracking the water tank and cooling pipelines. It is judged as an unqualified sample.

- Concentrated coolant test: The concentrated coolant cannot be directly added to the engine. After testing the original freezing point of the concentrated coolant, it needs to be diluted with deionized water according to the ratio, and the actual freezing point after dilution is calculated, and then it is evaluated whether it meets the vehicle usage requirements.
The instrument will automatically store the date, time, sample number, expected freezing point, and actual freezing point of each test group. It can be printed on-site in paper reports or export all historical data to a USB drive for record-keeping. Multiple parallel sample tests showed that the difference in the two ice point measurements of the same sample was controlled within 0.2℃, which proved that the instrument's detection data was stable and reliable. If the difference between the parallel sample values is too large, it is necessary to check the cleanliness of the test tube, the alcohol level, and the installation position of the sensor. After eliminating external interference, re-measurement should be conducted.