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D5188-23 – Standard Test Method Technical Guide
📐 Test Scope and Applicability
ASTM D5188 −23 defines a standardized procedure for determining the temperature at which the vapor formed from an air-saturated, chilled sample produces a pressure of exactly 101.3 kPa (one atmosphere) against a vacuum. The method applies specifically to volatile petroleum products, including gasoline and gasoline-oxygenate blends, that are saturated with air at a temperature of 0 °C to 1 °C (32 °F to 34 °F).
This test method is valid for samples yielding a determined temperature strictly between 36 °C and 80 °C (97 °F to 176 °F), with a targeted vapor-liquid ratio ranging from 8:1 to 75:1. While primarily designed for clear fuels, hazy samples observed during chilling must be explicitly identified in the report, though precision data for such cases has not yet been established.
⚙️ Test Method Summary: Evacuated Chamber and Piston Based Method
The core procedure relies on introducing a precisely measured, chilled volume of air-saturated sample into a thermostatically controlled test chamber. The system may utilize an evacuated chamber of a fixed known volume or a chamber equipped with a moveable piston to accommodate volume expansion after sample introduction. The sample is heated steadily until the internal vapor pressure reaches the specified equilibrium point of 101.3 kPa. The temperature recorded at this precise equilibrium is the definitive measurement.
| 🟦 Parameter | 📏 SI Specification | 📐 Imperial Equivalent |
|---|---|---|
| Sample Air-Saturation Temperature | 0 °C to 1 °C | 32 °F to 34 °F |
| Standard Test Pressure | 101.3 kPa | 14.69 psia (1 atm) |
| Valid Vapor-Liquid Ratio Range | 8 : 1 to 75 : 1 | 8 : 1 to 75 : 1 |
| Valid Temperature Range for Result | 36 °C to 80 °C | 97 °F to 176 °F |
💡 Correlation with Historical Method D2533: When the vapor-liquid ratio is specifically conducted at 20:1, the result from this test method is intended to be directly comparable to results determined by the withdrawn Test Method D2533 (see ASTM D5188-23, Note 1). The method may also be applied at pressures other than one atmosphere, but the standard precision statements may not apply under those conditions.
📊 Key Measured Parameters and Definitions
The standard establishes critical terminology for reporting and interpreting results. The primary derived value is T(V/L = 20), which represents the equilibrium temperature at which the partial pressure of the sample under test conditions equals 101.3 kPa at a 20:1 ratio. The more general property, the vapor-liquid ratio of a fuel, is defined as the ratio of the volume of vapor in equilibrium with the liquid to the volume of the original liquid sample charged at 0 °C.
| 🎯 Term | ⚡ Definition per ASTM D5188-23 |
|---|---|
| T(V/L = 20) | Equilibrium temperature at 101.3 kPa (14.69 psia) with a 20:1 vapor-liquid ratio. |
| Vapor-Liquid Ratio of a Fuel | Ratio of vapor volume in equilibrium with liquid to the volume of the sample charged as a liquid at 0 °C (32 °F). |
⚠️ Hazy Sample and Applicability Warning: Some gasoline-oxygenate blends may develop a haze when cooled to the required saturation temperature of 0 °C to 1 °C. If a haze is observed per Section 12.5 of the standard, it must be strictly indicated in the reporting of results. Precision and bias statements for hazy samples have not been determined, and results generated outside the standard temperature or pressure ranges may not meet the stated precision.
❓ Frequently Asked Questions
🔍 What does the term T(V/L = 20) specifically represent?
It is the specific equilibrium temperature determined by the method where the partial pressure of the volatile fuel sample equals exactly 101.3 kPa (one standard atmosphere) while the vapor-liquid ratio within the test chamber is strictly maintained at 20:1.
💡 How does this method compare to the older Test Method D2533?
ASTM D5188-23 is intended to produce results comparable to D2533 specifically when testing is performed at a 20:1 vapor-liquid ratio. This modern method utilizes evacuated chamber or piston-based equipment to conduct the measurement.
⚡ What types of fuel samples are suitable for this test?
The test method is applicable to volatile petroleum products, specifically gasoline and gasoline-oxygenate blends. The sample must be capable of being saturated with air at 0 °C to 1 °C for the defined volume charging procedure.
📌 What are the absolute limits for the determined temperature?
To be considered strictly within the scope of the standard, the determined temperature for the vapor-liquid ratio must fall between 36 °C and 80 °C (97 °F and 176 °F). Furthermore, the selected vapor-liquid ratio must lie between 8:1 and 75:1.