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D1740-01 – Standard Test Method Technical Guide
🔬 Test Principle and Apparatus
The ASTM D1740-01 test method covers the measurement of flame radiation characteristics of aviation turbine fuels and other similar distillate fuels. The core result is expressed as a Luminometer Number, defined as a measure of flame temperature at a fixed flame radiation in the green-yellow band of the visible spectrum. A high luminometer number indicates a fuel of low radiation characteristics. This test method has been adopted for use by government agencies to replace Method 2108 of Federal Test Method Standard No. 791b.
The apparatus used is the ASTM-CRC Luminometer, which consists of three main parts: a small wick-type lamp in which the sample is burned, an optical filter and photocell circuit that indicates the intensity of flame radiation in the range from 4800 to 7000 Å, and a thermocouple placed just above the flame to measure the temperature rise across the burner. The test relies on a pair of reference fuels to anchor the measurement scale.
⚙️ Procedure and Calculation Method
The procedure involves burning the fuel sample in the ASTM-CRC Luminometer lamp and obtaining a curve of flame radiation against the temperature rise (ΔT). To ensure that the constant rating level is the same in all units, it is defined as the smoke point of tetralin. The Luminometer Number (LN) is then calculated by comparing the test fuel’s performance to the reference fuels.
| 🟦 Fuel Type | 📏 Luminometer Number (LN) | 🎯 Test Role |
|---|---|---|
| Isooctane (Reference) | 100 (Scale Maximum) | Low radiation standard (highest ΔT) |
| Tetralin (Reference) | 0 (Scale Minimum) | High radiation standard (lowest ΔT) |
| Test Fuel Sample | LNTest | LN = (ΔTTest − ΔTTet) / (ΔTIso − ΔTTet) |
⚠️ Regulatory Status Note: Per the standard’s Note 1, Subcommittee J intended to ballot for withdrawal of this test method when due for reapproval in 2006, citing very limited and declining use for determining compliance with aviation turbine fuel specifications. Users should verify the current version and regulatory applicability before use. Specific safety precautions are also listed in Sections 7.1, 7.2, 8.1, 8.2, and Annex A1.1.
📊 Applications and Correlations
The test provides an indication of the relative radiation emitted by the combustion products of gas turbine fuels from a diffusion flame. This radiation level is related to the hydrocarbon type composition of the fuel. Because radiant heat transfer exerts a strong influence on the metal temperature of combustor liners and other hot section parts of gas turbines, the Luminometer Number provides a direct basis for correlating fuel characteristics with the operational life of these critical engine components.
There is a well-documented correlation between the Luminometer Number and the Smoke Point (Test Method D 1322), which is detailed in Appendix X1 of the standard. This allows for cross-referencing combustion quality data.
| 🟦 Property / Standard | ⚡ Relationship & Significance |
|---|---|
| Smoke Point (D 1322) | Good correlation with Luminometer Number (see Appendix X1). Provides an alternative measure of combustion quality. |
| Radiant Heat Transfer | High Luminometer Number indicates lower flame radiation, which reduces thermal stress and extends the life of combustor liners. |
| Fuel Specification | Referenced in Specification D 1655 (Aviation Turbine Fuels) and D 2880 (Gas Turbine Fuel Oils) for fuel characterization. |
💡 Technical Insight: While correlated, the Luminometer Number and Smoke Point measure different phenomena. The LN measures flame temperature at a fixed radiation level, while the Smoke Point measures the maximum smokeless flame height. The LN scale is specifically anchored by the smoke point of tetralin to ensure consistency across different apparatus units.
❓ Frequently Asked Questions
🔍 What is a Luminometer Number?
It is defined as a measure of flame temperature at a fixed flame radiation in the green-yellow band (4800 to 7000 Å) of the visible spectrum. A high Luminometer Number indicates a fuel with low radiation characteristics.
💡 How is the Luminometer Number calculated?
It is calculated from the difference in temperature rise (ΔT) between the test fuel and tetralin, divided by the difference in ΔT between isooctane and tetralin. The scale is anchored so that isooctane equals 100 and tetralin equals 0.
⚡ What is the relationship between the Luminometer Number and engine life?
Flame radiation strongly influences the metal temperature of combustor liners and hot section parts. A higher Luminometer Number (lower radiation) correlates with reduced thermal stress and potentially longer component life.
📌 What fuels are covered by this standard?
The standard covers aviation turbine fuels and other similar distillate fuels. It is applicable to fuels covered under specifications such as D 1655 (Aviation Turbine Fuels) and D 2880 (Gas Turbine Fuel Oils).