Issue #269 Putting Your Bike on the Wagon
Where did those cryptic octane ratings come from, and what do they really mean? Robert Smith connects the dots from the early days at the DuPont lab to potential problems with Ducati tanks.
Ethanol is beguiling stuff, especially when flavoured with juniper berries and served ice cold over an olive. And while we’ve been drinking it mixed in various forms for at least 10,000 years, it’s only recently our motorcycles have also taken to quaffing it.
First, a little history. In the beginning, gasoline consisted mostly of n-heptane and iso-octane. The more iso-octane in the mixture, the more resistant the fuel was to explosive combustion, allowing higher compression ratios and better thermal efficiency. Pure iso-octane has an octane rating, by definition, of 100, hence the “octane rating,” but oil fractionation produces much less iso-octane than n-heptane, so higher octane fuels cost more. In 1921, Charles F. Kettering at DuPont discovered that adding tetraethyl lead to gasoline increased the octane rating, and TEL became the octane enhancer of choice.
It wasn’t long before problems arose. In 1924, 17 refinery workers died “violently insane” from severe TEL poisoning; then childhood mental problems became linked to lead levels in the air around highways. Volatile lead compounds from car exhausts were implicated, leading to a ban on TEL as a fuel additive in most countries.
Around the same time, smog levels in major cities became a concern. Smog is most usually caused by the action of sunlight on the mixture of carbon monoxide, nitrogen oxides and unburned hydrocarbons from auto exhausts, and in sunny California cities it’s literally a killer, especially of the elderly and those with breathing issues. That led to catalytic converters (to convert CO to CO2) and a call for oxygenated fuels that would produce less CO in the first place.
The first octane booster/oxygenator used widely was MTBE, methyl tertiarybutyl ether, but that was implicated in groundwater contamination and soon dropped. Since then, all kinds of chemicals have been tried. Some gas companies have used methylcyclopentadienyl manganese tricarbonyl, but MMT isn’t good for catalytic converters, and also has health concerns. It’s been subject periodically to restrictions and bans, though it’s legal in the US at the moment. Benzene (up to one per cent) and toluene are also commonly used as octane enhancers in higher octane fuels, but they don’t oxygenate, and benzene is also carcinogenic.
What the marketplace was looking for was an additive that was an octane booster as well as an oxygenator while also being environmentally responsible and with no health issues. Ethanol seemed to be the answer. As a gas additive, it reduces CO emissions and increases octane rating.
Thanks to genetic modification, crop science and farm subsidies, the US produces far more corn than it can eat, which is why corn ends up as additives like high fructose corn syrup, as an ingredient in American beer, and as cattle fodder. Fermented to ethanol, corn seems to be the perfect fuel: clean, green—and not dependent on imported oil. In the US, 10 per cent ethanol fuel, known as E10, is now the default option in many states.
So ethanol is good, right? Well maybe. Environmentalists have pointed out the “inconvenient” evidence that it actually takes more imported oil to grow the corn (in the form of oil-derived fertilizers and pesticides) and ferment it to ethanol than if the oil had gone straight to the refinery. E10 certainly reduces smog and enhances octane, but its energy content is lower than straight gas, so you burn more.
The ethanol in E10 gas also makes it hygroscopic, meaning it attracts moisture. E10 will hold as much as 0.5 per cent water at 21C, and its proponents claim this makes it useful in preventing fuel line freeze-ups by keeping water in solution. Unfortunately, when the temperature drops to 0C, as it sometimes will in Canada, E10 will only hold 0.3 per cent moisture, so half the water separates out (“phase separation”). Then you have liquid water in the bottom of your gas tank. Bad news for steel tanks, sure: but it gets worse.
Many modern motorcycle gas tanks are rotational moulded from polyamides, usually Nylon 6. Nylon 6 both absorbs moisture and allows it to pass through (its moisture vapour transmission rate, MVTR, is higher than many other plastics). When Nylon 6 absorbs moisture, it swells, and thin sections in, say, a moulded gas tank can distort. Ducati and Aprilia use Nylon 6 gas tanks manufactured by Acerbis, and Ducati has been quietly replacing gas tanks on Multistradas, Sport Classics and some Monsters on which the owners claim their gas tanks have swollen and distorted.
What to do? Ducati’s stated position is that ethanol is an “additive” to gasoline, and prohibits owners from using E10 on pain of voiding their warranty. And this may just be a one-off incident, because my 2000 Sprint ST also has a Nylon tank, and I’ve never had a problem. Mohawk (now Husky) gas has had 10 per cent ethanol in its premium grades for at least 20 years, and I know the ST has seen plenty of it. On the other hand, Bombardier Recreational Products in the form of its Evinrude watercraft subsidiary, has also warned owners not to use E10.
Can you avoid ethanol? The last information I have is that, in Canada, Shell’s 91 octane and Chevron’s 94 are both ethanol free. Petro-Canada varies by province. Look for a yellow label advising the ethanol content. For more information, visit: www.pure-gas.org.
Overall, I think I prefer alcohol in my glass, not my gas tank. Cheers!
