Because there have been articles which have recently stated that we need corn ethanol as an octane booster in our gasoline, I am reposting a segment of the interview I did in 2014 of Bill Reinert, a newly retired Toyota energy engineer who was for many years their leading company spokesperson on alternative fuel vehicles and research, and who was involved in the design of the Prius.
K.M.: Ethanol got its window of opportunity as a methyl teriary-butyl ether (MTBE) replacement, because MTBE was added to gasoline to help prevent air pollution and then it was discovered that it was a water pollutant and a carcinogen. Now, ethanol advocates like to tell us that we need ethanol as an oxygenator and octane booster in our gasoline. Are there good alternatives to ethanol that might be used as octane boosters instead? What would you pick?
Reinert: I’d pick the bioethers. They’re not water contaminants and their half-life in the troposphere is very small. With a little more study I think they can make a contribution in improving the cetane and the octane of the fuels and thus allow us to use them in the most advanced engines that we have right now. The trade off with ethanol as an octane enhancer is that it’s hydroscopic and I would never make that choice, plus it has such a giant footprint. In comparison, we can make these ethers pretty quickly and pretty easily.
The bioethers, dimethyl ether (DME) and diethyl ether (DEE), are synthesis gases made from waste products, not corn. Since they’re not a fermentation product, all of the carbon gets turned into fuel whereas in fermentation, only the carbon that is converted into sugar gets used for fuel. DEE can be used in gasoline engines as an octane enhancer and DME could be used to increase the cetane of diesel, or, it could replace diesel altogether.
Octane boosters help prevent pinging in the advanced gasoline engines since we’ve increased the combustion temperatures so high that the fuel pre-ignites. This means that new gasoline engines have started to resemble diesel engines.
And in order to reduce the nitrogen oxide emissions from the diesel engine, we are reducing its combustion ratio, making it more like the gasoline engine. However, this produces soot, which DME can help to prevent.
I’ve had some wonderful conversations with Steve Chu and others at the DOE and what they want is a drop in gasoline replacement. Ideally, we would be given optimum specifications, or fixed properties, for gasoline and diesel. There would be multiple pathways to arrive at those specifications, such as through syngas. This could be done through a Defense Advanced Research Projects Agency (DARPA) grant. The fuel you’d want to pick in the end would be the one with the lowest societal costs. This is what we really need to be doing, but unfortunately, we’re not doing it.
I'd like to add a few additional comments. In Europe, Britain, Australia, and Canada corn ethanol is not used to increase octane levels in fuel supplies. In those places, they are using benzene, toluene, and MTBE. Here, in the U.S. we banned MTBE because it polluted ground water where gasoline tanks leaked, especially in California. Canada continues to use MTBE as octane booster. Corn ethanol policy contributes to vast amounts of groundwater contamination throughout the corn belt, sadly, so trading ethanol for MTBE is questionable, at best.
It is desirable to have engines that run more efficiently on higher octane fuel, and catalytic converters are used to help mitigate the air pollution from these toxic substances which boost the octane levels. The ethanol plants themselves, as well as other chemical plants which produce the octane boosters also have air quality issues.
Fuel cell vehicles have clean exhaust, and, some cities that want to incentivize electric cars also hope that would lead to cleaner air, like where I live along the front range of Colorado. Unfortunately, then, the pollutants and greenhouse emissions are outsourced to where the electrical plants exist and to where the batteries are produced.
Perhaps this subject (octane boosters) is an area for further research and innovation as we work towards improving our transportation and reducing our greenhouse emissions.
A government study of ethanol's role in ozone pollution is urgently needed, too, after the finding in Brazil which tied ethanol use to high ground ozone pollution levels. --K.M.