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• Oil & Alternative Fuels

• Engine Fuel Quality

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• Delivering Quality
• Amendment Regulations 2003
• Spec Regulations 2002
• Spec Regulations 1998
• Biofuel Blend Waivers
• Fuel Quality in NZ 1992-1999
• Cetane Number of NZ Diesel
• Diesel Carbon Residue
• Regulating Biofuel Quality
• Review of Permitted Sulphur
• Lower Sulphur Diesel

The Ministry of Commerce manages the FQM programme to monitor diesel and petrol quality by taking fuel samples from service stations and having them tested. A formal statistically based sampling plan is used to ensure that there is adequate geographical coverage and that an acceptable likelihood of detecting non-compliance is maintained. Sampling and testing are carried out by qualified contractors.

The Regulations specify many properties of diesel fuel including cetane number (CN) and cetane index (CI).

CI is a useful tool for predicting CN when used with due regard for its limitations. However the relationship between CI and CN depends on how the diesel is made. The FQM programme routinely uses CI determined using ASTM D 976 in diesel quality monitoring because of the expense and logistical difficulties of CN measurement. This study investigates how useful CI is as an approximation to CN for diesel supplied in New Zealand.

A newer method, ASTM D 4737, for determining CI is available. However this method is not recognised by the Regulations. This study investigates whether there might be an advantage in specifying this method in Regulations.

The following are the main findings of this study:

1. All samples complied with CN, CI₉₇₆ and density requirements.
2. There was significant variation in both CN and CI₉₇₆ during the test period.
3. CI₉₇₆ is greater than CN by 1.5 to 2 for most samples even though the fuel comes from a variety of sources. However the relationship is highly variable within this range.
4. Samples collected in the area supplied from the Auckland terminal, which are likely to have come from the Marsden Point refinery, have a CI₉₇₆ 1 to 1.5 higher than their CN.
5. The average difference between CI₄₇₃₇ and measured CN is greater than the difference between CI₉₇₆ and measured CN.
6. The current method ASTM D 976 has its limitations, but generally gives a closer fit than ASTM D 4737. Therefore there is no compelling reason to change the test method in the Regulations at this time.
7. The difference in CI results between the two laboratories, Inspectorate and BP Laboratory, was small. This indicates a good overall agreement between the two laboratories, and also indicates that samples did not deteriorate during storage and transport.