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D6422-99 – Standard Test Method Technical Guide
📐 Scope and Significance
This test method, designated D6422-99, covers the ability of gasoline-alcohol blends to retain water in solution or stable suspension at the lowest temperature they are expected to encounter during storage or use. It is specifically designed for blends containing saturated C1 to C4 alcohols only and does not apply to primary alcohol fuels like M85 or Ed85, or gasoline-ether blends. The test measures the temperature at which phase separation occurs, defined as the formation of two distinct layers: a lower aqueous phase and an upper hydrocarbon phase. Haze formation is not considered phase separation.
The significance of this test lies in the limited water retention capacity of gasoline-alcohol blends, which is highly temperature-dependent. Exceeding the water tolerance limit leads to phase separation, which can compromise fuel performance. This test method helps determine the safe storage and use conditions for such blends.
⚙️ Test Procedure and Requirements
The sample is cooled at a controlled rate to its lowest expected storage or use temperature. The apparatus from Test Method D2500 or a dry ice-isopropyl alcohol bath is used. A maximum cooling rate of 2°C (4°F)/min is specified, as phase separation can have a long but unpredictable induction period. The sample is observed periodically for phase separation.
Phase separation is identified by the formation of two layers, with droplets visible to the unaided eye clinging to the sides or bottom of the container. Test specimens meeting this criterion are considered phase separated. Haze alone does not indicate phase separation.
| 🔍 Criteria | 📐 Description |
|---|---|
| Phase Separation | Formation of two distinct layers: lower aqueous and upper hydrocarbon |
| Droplets | Visible droplets clinging to sides or bottom indicate separation |
| Haze | Not considered phase separated |
| ⚡ Parameter | 🎯 Value |
|---|---|
| Maximum Cooling Rate | 2°C/min (4°F/min) |
| Cooling Apparatus | Per D2500 or dry ice-isopropyl alcohol bath |
| Observation Frequency | Periodic |
⚠️ Safety Notice: This standard involves hazardous materials, operations, and equipment. Users are responsible for establishing appropriate safety and health practices and determining applicable regulatory limitations.
💡 Technical Tip: Adhere to the maximum cooling rate of 2°C/min to ensure accurate phase separation detection, as rapid cooling may mask the true separation temperature.
❓ Frequently Asked Questions
🔍 What is phase separation in gasoline-alcohol blends?
Phase separation is the formation of two distinct layers: a lower aqueous layer and an upper hydrocarbon layer. It occurs when the water content exceeds the blend’s tolerance, which is temperature-dependent.
💡 How is the test conducted?
The fuel sample is cooled at a controlled rate of 2°C/min using a specified apparatus, and observed for phase separation. The temperature at which separation occurs is recorded.
⚡ What fuels are applicable?
This test is applicable to gasoline-alcohol blends with saturated C1 to C4 alcohols. It does not apply to fuels with alcohol as the primary component, like M85 or Ed85, or gasoline-ether blends.
📌 Why is the cooling rate limited to 2°C/min?
Phase separation in gasoline-alcohol blends can have a long and unpredictable induction period. A slow cooling rate ensures accurate measurement of the separation temperature.