The Road to High Octane Fuels

by Jeremy Martin (Union of Concerned Scientists) ... 9 things you need to know about high octane fuel, and my perspective on a path forward.

... But in the context of engines, octane is a standard measurement for fuels that describes their ability to burn without knocking in high compression engines[1]. Higher octane fuels allow for engines to operate at higher compression ratios, which improves power and performance. When gasoline is first distilled from oil it has an octane number of about 70. But such a low octane fuel would severely limit the efficiency of engines, so refinery processes and additives are used to raise the octane number to about 87 for regular gasoline and 91 for premium[2].

... Automakers are increasingly adopting turbocharging and other engine technologies to improve power and fuel efficiency, and these technologies work better with higher octane fuel[3]. However, the higher prices of high octane fuel available now discourages consumers from purchasing it, limiting its use primarily to luxury or high performance vehicles. If higher octane fuel was widely available at attractive prices, automakers could squeeze more performance and efficiency out of technologies they are already starting to use.

... Over the last decade, ethanol has become a major high octane fuel additive. Today most of the gasoline sold in the United States has 10% ethanol, but if the ethanol blending level was increased from 10% to 30% without making other changes in the fuel, the octane rating would increase by about 6 points (or from 87 to 93)[4]. Moreover, ethanol is generally less expensive than gasoline, so higher ethanol blends could be sold for less than conventional gasoline, offering the promise of higher octane fuel for lower prices.

... Ethanol plays two roles in gasoline blends, acting as an additive to increase octane, and also acting as source of energy. In E10, ethanol is a cost competitive source of octane, and without ethanol, refiners or blenders would need to increase the use of other high octane blending components that are more expensive than ethanol[7]. But in E85 ethanol makes up the majority of the fuel, and in this case the lower energy density of ethanol compared to gasoline results in FFVs getting about 25% fewer miles per gallon on E85 than E10.

High octane ethanol blends used by optimized vehicles balance higher octane against lower energy

... According to recent studies, an optimized high compression engine using a high octane ethanol blend of between 20-40% ethanol would have an efficiency gain that approximately offsets the lower energy content of the blended fuel[8]. ...

If everything works as planned, drivers could buy cheaper fuel without a mileage penalty, automakers would see a greater benefit from emissions reducing technologies like turbocharging that they are already introducing, the efficiency of the combined vehicle fuel system would improve and emissions would fall.

... Automakers have to start selling optimized vehicles, gas stations have to make the high octane fuel available for these optimized vehicles while continuing to provide appropriate fuel for the existing fleet, and fuel producers and distributors have to adjust their operations to match the evolving demand. This kind of transition may seem challenging, but we have changed our fuel blends several times in the past, including dramatic changes like replacing leaded gas with unleaded and changes that happened behind the scenes such as reducing sulfur. With coordination, advanced planning, and appropriate consumer education, this can be a manageable process, but it cannot happen overnight.

Because of the ongoing progress on fuel efficiency, the cars being sold between 2026 and 2036 will be much more efficient than the cars they are replacing, and this means total fuel use will be falling. For example, if a car sold in 2016 that gets 25 miles per gallon of E10 is replaced in 2026 with one getting 50 miles per gallon of E25 it will use just 25% more ethanol, and almost 60% less petroleum, to drive the same distance as the car it replaces[10].

Getting the maximum climate benefit from each gallon of ethanol means moving beyond corn

... The U.S. has plenty of biomass resources to produce enough cellulosic ethanol for mid-level blends without using any more corn, but commercial production of cellulosic ethanol just started recently. It will take several more years until billions of gallons of cellulosic ethanol are available for blending into high octane fuels. Precisely how quickly cellulosic ethanol scales up depends a lot on investors’ perception of the future demand for ethanol, ....

Fool me twice? Snatching defeat from the jaws of victory with fuel economy loopholes

A lot of vehicle efficiency experts are deeply skeptical about high octane ethanol blends because of a bad experience with flex fuel vehicle (FFV) policy. READ MORE