The new hydrogen quality specification covers combustion engines
The hydrogen quality standard has a second edition with grades for combustion engines — vehicular and stationary — alongside the fuel cell requirements. In an interlaboratory comparison only three of thirteen laboratories stayed within the permitted deviations.
- Requirements used to be written mainly for fuel cells; two grades for combustion engines have now been added — for vehicles and for stationary applications.
- A fuel cell is damaged by trace amounts of sulphur or carbon monoxide, so it needs hydrogen of almost laboratory purity.
- A combustion engine is less sensitive to those but tolerates water and particulates far worse — hence separate grades instead of one strictest set of requirements.
- The determinations cover sulphur compounds, nitrogen compounds, hydrocarbons, carbon monoxide and dioxide, water, oxygen and particulates — all at fractions of a part per million, in gas under high pressure.
- In an interlaboratory comparison only three of thirteen laboratories stayed within the permitted deviations for all determinations.
- The difficulty lies not in the measurement itself but in taking and storing the sample without contaminating it.
- Hence the emphasis on sampling vessels and procedures, calibration gases with adequate uncertainty and regular participation in comparisons.
Source: ISO