• Froth Volume and Collapse Time
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Fuel foaming can be a real irritation at the pumps, particularly for drivers of light vehicles, so the fuel companies have been adding anti-foaming agents to diesel for the past few years.
Last year's test showed a useful reduction in froth levels but the problem is still present, so this year we devised a more stringent test. Air was bubbled through a fuel sample at a controlled rate for a fixed time and the initial volume of foam produced was measured. The air was turned off and the time taken for the foam to collapse was measured.
We were surprised to find enormous variation in the foaming behaviour of the samples.
Some produced over a litre of froth, which took half a minute to collapse while others (notably both Esso samples) produced minimal, short-lived foam. The supermarket samples were mediocre performers which was unfortunate given their target market of private car drivers.