ASTM D7171 Standard Test Method for Hydrogen Content of Middle Distillate Petroleum Products by Low-Resolution Pulsed Nuclear Magnetic Resonance Spectroscopy
4. Summary of Test Method
4.1 A test specimen is analyzed in a pulsed NMR spectrometer calibrated with reference standard materials. The analyzer records in a nondestructive fashion the total NMR signal, which arises from the absolute amount of hydrogen atoms in the reference standards and test sample. The absolute hydrogen signal intensity reported by the pulsed NMR instrument for the standard and test specimens is normalized by the corresponding sample mass. The resulting signal-per-gram ratios are used as a means of comparing theoretical hydrogen contents of the standards with that of the sample. The result is expressed as the hydrogen content (on a mass % basis) of the sample.
4.2 To ensure an accurate measure of the absolute hydrogen content of the reference standards and sample, it is necessary to ensure that the measured hydrogen signal intensity is always directly proportional to the absolute hydrogen content of the standards and sample.
4.3 Undercounting of the reference standard with respect to the sample is avoided by a number of strategies, including accurate filling into the linear response region of the sample compartment so that the mass recorded for the sample represents the true amount measured by NMR, and use of a recycle delay considerably greater than the longest relaxation time constant (T1) for the sample.
5. Significance and Use
5.1 Hydrogen content represents a fundamental quality of a petroleum distillate that has been correlated with many of the performance characteristics of that product. Combustion properties of gas turbine fuels are related primarily to hydrogen content. As hydrogen content of these fuels decreases, soot deposits, exhaust smoke, and thermal radiation increase. Soot deposits and thermal radiation can increase to the point that combustor liner burnout will occur. Hydrogen content is a procurement requirement of the following military fuels: JP-5 specified in MIL-DTL-5624, JP-8 specified in MIL-DTL-83133, and Naval Distillate Fuel specified in MIL-DTL-16884.
5.2 This test method provides a simple and precise alternative to existing test methods (D3701, D4808, and D5291) for determining the hydrogen content of petroleum distillate products.
