GM Vice President Dan Nicholson addresses the gathering August 2, 2016 at the Center for Automotive Research Management Briefing Seminars in Traverse City, Michigan.

During an address to the American Fuel and Petrochemical Manufacturers, General Motors’ vice president of global propulsion systems called for premium gasoline to become the new baseline going forward to enable more efficient engines. This is hardly a new idea, but it comes as a bit of a surprise right now as GM wages a battle on two fronts with announced plans for 20 new zero-emissions vehicles in the next five years while also consulting with the Trump administration on changes to fuel economy standards.

In his talk, Nicholson reiterated his company’s electrification plans but also suggested that this is the right time to make a move toward making 95 RON gasoline the new minimum standard as it generally is in Europe. Fuel octane ratings are an indicator of the fuel’s resistance to self-ignition or knocking. The are two generally accepted methods of testing this, motor octane (MON) and research octane (MON). The pump octane number (PON) that appears on gas pumps in North America is the average of the two with regular typically being labeled as 87 PON and mid-grade as 91 PON. A fuel with a rating of 95 RON will typically have a PON of 91, the standard for premium fuel.

Fuel retailers have long marketed the idea that using premium fuel can help improve fuel economy and this is true up to a point. Engines will only see a benefit if they are optimized for this fuel with either a higher compression ratio or more turbocharger boost. This enables a higher expansion ratio in the engine so each cylinder firing extracts more work from the fuel. Unfortunately, putting higher octane fuel in a lower compression engine will probably have little or no impact in most cases.

According to Nicholson, relatively simple changes including new pistons to enable higher compression and revised calibrations can yield about a 3% improvement in efficiency with no significant added component costs. Aggregated over millions of engines a year, that adds up to some fairly substantial fuel consumption reductions.

But is is worth it for the consumer?

The consumer side of this equation is where things get a little muddier. While a 3% savings in fuel use is not insignificant for manufacturers that at least for now need to continue improving their efficiency across their fleets, consumers might not see the full benefit. The upfront cost for a vehicle optimized to run on 95 RON gasoline may be essentially the same as one that runs on regular, and there would be no added infrastructure costs, but the consumer may be paying more every time they go to the pump.

For the week of March 5, 2018, the Energy Information Agency reported national average retail gasoline prices of $2.56/gallon while premium was $3.08, a difference of $0.52. The projected average fuel economy for 2017 model year vehicles was 25.2 mpg. Over 100,000 miles, that would amount to about 3,968 gallons of gasoline. A 3% bump  would take that to 26 mpg and 3,852 gallons a savings of just 116 gallons. At $3.08 per gallon that would save $357 while the the premium fuel would cost more than $2,000 more than regular.

Previous | Next