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D5191-22 – Standard Test Method Technical Guide
⚗️ Scope and Applicability
ASTM D5191-22 specifies the procedure for determining the total vapor pressure of volatile petroleum products and liquid fuels using automated instruments. It covers spark-ignition fuels with oxygenates and ethanol blends up to 85% (volume fraction). The method is applicable for samples with boiling points above 0 °C (32 °F) that exert a vapor pressure between 7 kPa and 130 kPa (1.0 psi and 18.6 psi) at a standard temperature of 37.8 °C (100 °F) and a vapor-to-liquid ratio of 4:1. Measurements are conducted on liquid sample sizes ranging from 1 mL to 10 mL.
⚠️ Important Limitation: This test method is not validated for crude oil samples. For crude oil vapor pressure, refer to Test Method D6377 or IP 481.
⚙️ Test Procedure and DVPE Calculation
This “Mini Method” utilizes an automated apparatus to introduce a precise volume of chilled, air-saturated sample into a thermostatically controlled expansion chamber. The total vapor pressure is measured after the sample reaches equilibrium at the specified vapor-to-liquid ratio of 4:1.
This method calculates the Dry Vapor Pressure Equivalent (DVPE) for gasoline and gasoline-oxygenate blends using a specific correlation equation (Eq 1 in Section 14.2). This calculated DVPE closely approximates the dry vapor pressure obtained by Test Method D4953, ensuring regulatory and specification compliance for gasoline volatility.
| 🔢 Parameter | 📏 Specified Value |
|---|---|
| Test Temperature | 37.8 °C (100 °F) |
| Vapor-to-Liquid Ratio | 4:1 |
| Sample Size | 1 mL to 10 mL |
| Vapor Pressure Range | 7 kPa to 130 kPa (1.0 psi to 18.6 psi) |
| Ethanol Blend Limit | Up to 85 % (volume fraction) |
| Sample Boiling Point Minimum | Above 0 °C (32 °F) |
📊 Key Measured Properties and Precision
Gasoline-oxygenate blends may exhibit a haze when cooled to 0 °C to 1 °C. If a haze is observed during the chilling step (Section 8.5), it must be reported in the results. Precision and bias statements for hazy samples have not yet been determined per the standard’s interlaboratory studies. The standard also mandates a safety warning regarding mercury, which is designated by regulatory agencies as a hazardous substance; users must comply with all applicable laws regarding its use and disposal.
💡 Technical Note: The precision for this method was determined using 1 L containers (2003 ILS) and 250 mL containers (2016 ILS). The standard provides specific repeatability and reproducibility limits based on the vapor pressure level and container type used for sampling.
❓ Frequently Asked Questions
🔍 What is the DVPE and how is it calculated?
The Dry Vapor Pressure Equivalent (DVPE) is a calculated value derived from the measured total vapor pressure using the correlation equation (Eq 1) found in Section 14.2. This calculation adjusts the result to closely approximate the dry vapor pressure obtained by Test Method D4953.
💡 Is D5191 applicable to crude oil and all fuel blends?
No. The interlaboratory studies for D5191 excluded crude oil. For crude oil, use Test Method D6377 or IP 481. The method is validated for petroleum products and liquid fuels, specifically automotive spark-ignition fuels with ethanol blends up to 85% and vapor pressures between 7 kPa and 130 kPa.
⚡ What are the standard test conditions defined in the standard?
The measurement is conducted at 37.8 °C (100 °F) with a 4:1 vapor-to-liquid ratio. The sample must have a boiling point above 0 °C (32 °F), and the sample size for the automated instrument ranges from 1 mL to 10 mL.
📌 How should potential haziness in samples be addressed?
If a haze appears when the sample is cooled to 0 °C to 1 °C during chilling (Section 8.5), the analyst must document this observation in the test report. Precision and bias statements for hazy samples have not yet been established by the standard.