Call something “high-octane” and people know exactly what you mean: powerful. Intense.
It’s a term that comes from the gasoline business. Oil companies used to advertise the high octane rating of their fuel and its ability to prevent the dreaded “engine knock.” This phenomenon occurs when a mix of unburned fuel and air explodes prematurely in an engine, creating a pinging or knocking noise, and affecting mileage. Simply fuel up with premium-grade gas, the pitch went, and knock out the knock, while maximizing the bang from that gallon’s buck.
The reason premium is so magical? It has components that increase its resistance to combusting prematurely. This gives it a higher octane rating, which measures the fuel’s ability to resist engine knock. The higher the rating number, the more resistant the fuel is to creating knock.
Automotive technology has since muffled the problem. A sensor in modern engines detects the presence of knock and adjusts the timing of ignition to minimize it. Today, premium gasoline is a niche fuel, reserved for luxury cars with high-performance engines specifically optimized to run on higher-octane gasoline.
But what if every vehicle were to run on higher-octane gasoline? Would that make them more powerful—and more fuel-efficient as well?
Automakers are exploring that question as they try to meet the Corporate Average Fuel Economy (CAFE) standards goal set for 2025, which requires the overall vehicle fleet to hit 54.5 miles per gallon in fuel economy, with greenhouse-gas emission reductions alongside the target. More efficient vehicle engines designed to run on higher-octane fuels (HOF) could help them get there.
“You can make so much more torque and power with a higher-octane fuel,” says Brian West, who focuses on the fuel economy and emissions of high-octane fuel as a deputy center director of the Fuels, Engines and Emissions Research Center at the Oak Ridge National Laboratory (ORNL), Knoxville, Tenn. Engines designed to run on HOF are potentially up to 10% more fuel-efficient than those engineered for lower-octane gas.
While designing more vehicles that run on higher-octane premium-grade gasoline is one path toward meeting CAFE standards, it is also an expensive one for the consumer. Another option: Ethanol is a cheap, abundant octane booster that offers greenhouse-gas savings. What about engines that can run on a midlevel ethanol blend, such as E25 or E30?
“From an [automotive] enthusiast’s perspective, it’s brilliant,” says John Eichberger, vice president of government relations for Alexandria, Va.-based NACS and executive director of the Fuels Institute. “You get more power, more fuel efficiency, lower emissions—I think that’s fantastic. I like the idea of a high-octane optimized engine. “Where I start differing from the auto industry is how you get there.”
Higher Octanes to Come?
In the United States, a fuel’s octane rating is the average of two different performance testing methods: Research
Octane Number (RON) and Motor Octane Number (MON). On fuel pumps, this is indicated as (R+M)/2. Octane ratings vary by country; in the United States, premium is typically 91 to 93, with midgrade at 89 and regular at 87.
These octane levels alone, however—even for premium—are not anywhere near high enough for big efficiency gains in the current vehicle fleet.
“What we’re looking at today for future engines is a much higher octane than even today’s premium fuel,” says West. “We’re talking about something on the order of 95 or 96 on the same scale.”
How can engines take advantage of HOF? For one, even though a sensor in a conventional modern engine can detect and mitigate knock, this process negatively affects fuel economy. An engine specifically designed to run on high-octane fuel, however, is less prone to the problem to start.
HOF also allows manufacturers to downspeed and downsize the engine, offering efficiency gains. Downspeed refers to designing an engine to run at a lower, more efficient speed and higher load, or the flow of air through the engine, which also increases its efficiency. Downsize means exactly what it sounds like—a smaller engine. “With high-octane fuel, you can do a little of both,” says West.
According to ongoing research by ORNL, RON is a more accurate means of determining knock avoidance and, by association, leads to a more efficiently operating engine. So if they were to take advantage of HOF, automakers would target engines that run on gasoline with higher RONs.
“Today’s fuel is 91 RON, and we’re talking about going to 98 to 100,” says West. “An easy way to do that is just by adding
more ethanol. Ethanol has a really high octane number, so if you put 25% to 30% ethanol in today’s regular gasoline, then you would get close to that RON number.”
Engines designed to run on E25 or E30 could see fuel-efficiency gains of 5% to 10% compared to those that run on E10, according to ORNL’s research. This is big enough to offset any reduction in volumetric energy that is caused by ethanol’s lower energy density.
“If we’re talking about a more efficient engine, now we’re making better use of that energy so that a car designed for high-octane E25 tomorrow can get the same fuel economy as a similar vehicle today designed for 87 octane, E10,” says West.
Beyond efficiency gains, a move to midlevel ethanol blends would also meet other goals of the CAFE standards.
“You’re talking about a 5% efficiency improvement, which leads to a couple of really exciting things,” says West. “One, that gallon of ethanol doesn’t displace two-thirds of a gallon of gas—it displaces a full gallon of gas because I’m getting volumetric fuel-economy parity. And then the other thing is you get a really big greenhouse-gas advantage because your miles per gallon may actually be the same because the fuel is ethanol and not gasoline.”
CONTINUED: A Niche Fuel?
A Niche Fuel?
Despite the promise of engines optimized to run on HOF, the challenges are significant—and predictable.
“For the most part, high-octane fuel will be a niche fuel—it will be those individuals looking for greater power,” says Eichberger of NACS. “It won’t be available everywhere right away, so we’ll have a chicken-and-egg problem: how many vehicles are in the market and where the fuel is going to be dispatched.”
Although there are nearly 18 million fl ex-fuel vehicles (FFV), which can run on ethanol blends of up to 85%, they would serve more as bridge vehicles for midlevel blends such as E25 or E30. “They wouldn’t see a big fuel-economy benefit because they’re not really designed to take advantage of that, because the manufacturers today have to design their cars for the lowest available octane,” he says. “We’re talking about dedicated fuel for dedicated vehicles.”
Then there is fuel supply. Eichberger says E25 would not necessarily be an issue, but E30—which some automakers are advocating—would be.
From Eichberger’s perspective, the 5% difference between E25 and E30 is millions of dollars for retailers.
“Most of the fuel equipment is being listed for E25. If you want the fueling industry to help with the transition to bringing a new fuel like this to the market, you should probably think about optimizing your engines to something just below E25 so that you don’t have to impose on the infrastructure such incredible additional costs,” he says.
As retailers build new stores and replace their fueling equipment, they can install dispensers compatible with E25. Most underground storage tanks are likely already compatible. For E30, however, they would need to install E85-compatible equipment, which is much more expensive, says Eichberger.
“The infrastructure challenge should not be overlooked,” West acknowledges. Theoretically, blender pumps could be retrofitted to blend E25 from ethanol and E10, he says, while still providing 87-octane E10 to the 240 million legacy vehicles that would not be compatible with the higher-ethanol blend. Or the market could shift to a HOF without ethanol, such as premium. But there is a catch with that as well.
“The efficiency gains for the manufacturers would largely still be there, but the greenhouse-gas benefit would not be as good,” he says. “And I think it would be challenging for the refiners to produce really large volumes of that fuel.”
“We have a long way to go before understanding: Can we bring this to market in a way that will satisfy consumer demand, and will there even be any consumer demand?” says Eichberger. “The auto manufacturers have to demonstrate that latter part to us before the fueling industry says, ‘OK, let’s do this.’ ”
Hassling the HOF
There are several bumps in the road for the introduction of high-octane fuel (HOF) blends. What follows are what National Renewable Energy Laboratory (NREL) researchers consider major challenges to adopting HOF.
- Building supply and demand together is challenging.
- Ethanol investments face regulatory risks.
- Legacy vehicles could misfuel with HOF.
- EPA does not yet consider HOF a certification test fuel; it must be “readily available and used” first.
- Reid Vapor Pressure of E25 exceeds legal limits.
- HOF must be registered with EPA.
- Future CAFE calculation may not sufficiently reward HOF vehicles for improved efficiency.
- Cost of upgrading gas stations to offer HOF could be significant.
- If HOF price exceeds that of E10, its competitiveness will suffer.
Source: NREL
Members help make our journalism possible. Become a CSP member today and unlock exclusive benefits, including unlimited access to all of our content. Sign up here.