While our automobiles have experienced remarkable changes over the past several decades, the fuels we put in them have not. Specifically, the octane rating of regular gasoline today is the same as it was 40 years ago; in some areas of the country it is even lower.
From the 1920s to the early 1970s, fuel octane ratings increased in tandem with engine horsepower and compression ratios, culminating in the much-loved “muscle car” era of the late 1950s through early 1970s. But the octane rating of gasoline has stagnated ever since.
Modern and future engines need more octane — not less — to maximize fuel efficiency and reduce carbon emissions.
Smaller engines with increased compression ratios and turbocharging can significantly improve fuel economy while simultaneously providing the same — or greater — horsepower and torque of larger engines. However, these technologies also increase cylinder pressure, and that can lead to premature combustion of the fuel. Pre-ignition of the fuel causes “engine knock” or “pinging,” which can seriously damage engines.
That’s where octane comes into play. A fuel’s octane rating is a measure of its ability to resist premature combustion. The higher the octane number, the lower the risk of pre-ignition and engine knock. More octane also means more power.
These characteristics are appealing to automakers who face a serious challenge in the decade ahead. Federal Corporate Average Fuel Economy (CAFE) standards require automakers to manufacture vehicles that will achieve average fuel economy of 54.5 miles per gallon by 2025. That’s more than double the actual average of 24.3 mpg in 2014. Automakers are responding to these aggressive standards by exploring a broad range of technologies that can boost fuel economy. The most promising and economical approach identified by the automakers is to greatly expand the use of turbocharging and high compression ratio engines. And that will require an increase in the octane rating of our gasoline.
Accordingly, the auto companies are pleading for more octane. Just two weeks ago at the Society of Automotive Engineers World Congress in Detroit, GM’s vice president of propulsion systems underscored that “Higher octane is necessary for better engine efficiency. It is a proven low-cost enabler to lower CO2.”
There are a variety of options for increasing the octane rating of gasoline, but one octane source stands out from the crowd: ethanol.
Made from the starches and sugars in crops, waste and other biological material, ethanol is a renewable fuel that reduces CO2 emissions and has an incredibly high octane rating of 113. That compares to an octane rating of 84 for base gasoline produced at the refinery. In addition, ethanol costs less than other octane enhancers produced by oil refineries, many of which are toxic in nature.
Research by automakers and the Department of Energy confirms that gasoline blends containing 20-40 percent ethanol can provide the necessary octane boost for high-compression, turbocharged engines, while delivering better fuel economy than today’s gasoline. In the words of a Mercedes-Benz engineer, ethanol-based high octane fuels can provide “ridiculous power and good fuel economy.”
While upping the octane rating of regular gasoline would assist automakers in meeting new CAFE standards, it would also help petroleum refiners comply with the Renewable Fuel Standard. By requiring refiners to blend annually increasing volumes of renewable fuels with petroleum fuels, the RFS diversifies our nation’s energy mix and reduces demand for imported oil. Moreover, the RFS ensures oil refiners choose ethanol as the pathway to higher octane, rather than petroleum-based octane sources that increase air and water pollution.
Automotive technologies have experienced tremendous advancement in the past 40 years, but our fuels haven’t kept up. We need to modernize our fuel to reduce emissions and enable more efficient engines; higher octane is the key to accomplishing both of those goals. It’s past time to increase the octane content of our nation’s gasoline.
Tracey King is technical director of the Renewable Fuels Association.