86.308-79—Gas specifications.
(a) Analyzer gases.
(1)
Calibration gases for the CO and CO2 analyzers shall have zero grade nitrogen as a diluent. Combined CO and CO2 span gases are permitted. Zero grade nitrogen shall be the diluent for CO and CO2 span gases.
(2)
Calibration or span gases for the hydrocarbon analyzer shall be propane with zero-grade nitrogen as a diluent when testing gasoline-fueled engines. For Diesel engine tests the diluent shall be zero-grade air.
(3)
Calibration or span gases for the NOX analyzer shall be NO named as NOX with a maximum NO2 concentration of 5 percent of the nominal value. Zero-grade nitrogen shall be the diluent.
(4)
Zero-grade gases for hydrocarbon analyzers shall be nitrogen when testing gasoline-fueled engines and air when testing Diesel engines.
(5)
Zero-grade gases for the carbon monoxide, carbon dioxide and oxides of nitrogen analyzers shall be either zero-grade air or zero-grade nitrogen.
(6)
The allowable zero grade gas (air or nitrogen) impurity concentrations shall not exceed 2 ppmC hydrocarbon, 10 ppm carbon monoxide, 400 ppm carbon dioxide and 1 ppm nitric oxide.
(7)
“Zero-grade air” includes artificial “air” consisting of a blend of nitrogen and oxygen with oxygen concentrations between 18 and 21 mole percent.
(b) Calibration gas.
Calibration gas values are to be derived from NBS “Standard Reference Materials” (SRM's) or other gas standards approved by the Administrator. The uncertainty of the assigned calibration gas values shall not exceed 2.0 percent of the assigned value. The uncertainty is defined as the sum of the precision errors (at the 90 percent confidence level) and the bias errors. Precision and bias errors apply to both the equipment and the derivation procedures.
(c) Span gas.
Span gas values are to be derived from NBS “Standard Reference Materials” (SRM's) or other gas standards approved by the Administrator. The uncertainty of the assigned calibration gas values shall not exceed 3.0 percent of the assigned value. The uncertainty is defined as the sum of the precision errors (at the 90 percent confidence level) and the bias errors. Precision and bias errors apply to both the equipment and the derivation procedures.
(d) Hydrocarbon analyzer fuel—
(1)
The fuel shall contain 40 ±2 percent hydrogen. The balance shall be helium. The mixture shall contain less than 2 ppmC hydrocarbon.
(2) Alternate pure hydrogen fuel.
Some HFID's are designed to operate on pure hydrogen. Generally the HFID fuel is incompatible with good relative hydrocarbon response.
(i)
For Diesel engines this fuel is not recommended. However, this fuel may be used if the engine manufacturer demonstrates, on each basic combustion system (i.e., 4 cycle DI, 2 cycle DI, 4 cycle pre-cup, etc.) that an HFID using this fuel produces comparable results to an HFID using 40% H2 /60% He fuel. These data must be submitted to and approved by the Administrator prior to testing. Pure H2 fuel, that may be allowed for testing, must contain at least 99.0 percent hydrogen and contain less than 2 ppmC hydrocarbon.
(e) Hydrocarbon analyzer burner air.
The concentration of oxygen must be within 1 mole percent of the oxygen concentration of the burner air used in the latest oxygen interference check (%O2 I). If the difference in oxygen concentration is greater than 1 mole percent, then the oxygen interference must be checked and the analyzer adjusted if necessary, to meet the %O2 I requirements. The burner air must contain less than 2 ppmC hydrocarbon.
(f)
Oxygen interference check gases shall contain propane with 350 ppmC ±75 ppmC hydrocarbon. The concentration value shall be determined to calibration gas tolerances by chromatographic analysis of total hydrocarbons plus impurities or by dynamic blending. Nitrogen shall be the predominant diluent with the balance oxygen. Blends required for gasoline-fueled and Diesel engine testing are as follows:
| Applicability | O2 concentration (percent) | Balance |
|---|---|---|
| Diesel | 21 (20 to 22) | N2 |
| Diesel and gasoline | 10 (9 to 11) | N2 |
| Do | 5 (4 to 6) | N2 |
| Gasoline | 0 (0 to 1) | N2 |