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THE TESTS

17th February 1994
Page 37
Page 37, 17th February 1994 — THE TESTS
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Which of the following most accurately describes the problem?

• Cetane Index

This is a measure of ignition quality: the ease with which the fuel can ignite and release its energy. The higher the number, the more efficiently the engine can work, which should help fuel consumption and performance.

The cetane index is calculated from the distillation properties of the fuel, while the more accurate cetane number is found by experiment, using the fuel in a standard single-cylinder test engine. The cetane index only gives a rough indication of the cetane number of the base fuel, but some brands contain ignition improvers: additives which increase the cetane number while leaving the cetane index unchanged. Our test results were not quite as widely spread as before, but they all beat the industry recommended figure of 48.0, as well as the British Standard minimum index of 46.0. The average figure improved on last year's; in fact the average has been improving for the past three years.

Once again Shell was the star performer with a remarkable index of 55.0, significantly better than last year's winning 53.0, These figures give a rough guide to ignition quality, but Shell states that Advanced Diesel also contains ignition improvers so its actual cetane number should be even higher.

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