ASTM D5622 Standard Test Methods for Determination of Total Oxygen in Gasoline and Methanol Fuels by Reductive Pyrolysis
3. Summary of Test Method
3.1 A fuel specimen of 1 µL to 10 µL is injected by syringe into a 950 °C to 1300 °C high-temperature tube furnace that contains metallized carbon. Oxygen-containing compounds are pyrolyzed, and the oxygen is quantitatively converted into carbon monoxide.
3.2 A carrier gas, such as nitrogen, helium, or a helium/hydrogen mixture, sweeps the pyrolysis gases into any of four downstream systems of reactors, scrubbers, separators, and detectors for the determination of the carbon monoxide content, hence of the oxygen in the original fuel sample. The result is reported as mass % oxygen in the fuel.
4. Significance and Use
4.1 These test methods cover the determination of total oxygen in gasoline and methanol fuels, and they complement Test Method D4815, which covers the determination of several specific oxygen-containing compounds in gasoline.
4.2 The presence of oxygen-containing compounds in gasoline can promote more complete combustion, which reduces carbon monoxide emissions. The Clean Air Act (1992) requires that gasoline sold within certain, specified geographical areas contain a minimum percent of oxygen by mass (presently 2.7 mass %) during certain portions of the year. The requirement can be met by blending compounds such as methyl tertiary butyl ether, ethyl tertiary butyl ether, and ethanol into the gasoline. These test methods cover the quantitative determination of total oxygen which is the regulated parameter.
4.2.1 Only seven U.S. states have such wintertime requirements, and others with EPA approval have opted out of the program. The minimum oxygen limit now varies from 1.8 % to 3.5 % by mass. For methanol/heavier alcohol blend EPA waivers, the maximum oxygen content allowed is 3.5 % or 3.7 % by mass.
4.2.1.1 Only ethanol is used for such blending in the U.S. Ethers are banned by some states and are not used in all states because of water contamination issues.
