Make better use of higher-octane fuel, stop-start

As the industry pushes for better fuel economy, it's strange that two known mileage boosters -- higher-octane gasoline and stop-start technology -- aren't being exploited to their full potential.

There are obstacles to getting the full benefit from either, but those obstacles should be surmountable.

-- Octane: Higher octane improves combustion by allowing a higher compression ratio. But powertrain engineers can't squeeze the most compression out of regular gasoline because octane levels at the pump fluctuate. (That's why the pad you push to select a grade of gasoline at the pump hedges by saying "minimum octane rating.")

Greg Johnson, Lincoln brand powertrain manager, puts it this way: "We're limited by what is the mean octane rating of the fuel we're developing for."

Fuel-saving technologies such as turbocharging would be more productive if regular gasoline consistently had octane levels at the high end of its range, according to Stephen Ross, combustion technical leader at Ford Motor Co.

As the industry aims for 54.5 mpg corporate average fuel economy by 2025, the feds need to bring automakers and oil companies together to achieve consistent octane levels.

-- Stop-start: The problem here is regulatory: The EPA test for calculating CAFE doesn't measure stop-start benefits, and that has slowed penetration of stop-start systems. A stop-start system shuts off the engine when a car is stopped and restarts it when the driver releases the brake pedal.

Stop-start boosts fuel economy 8 to 10 percent, according to Mike Omotoso, senior manager for global powertrains at J.D. Power and Associates.

Brett Smith, co-director of the manufacturing, engineering and technology group at the Center for Automotive Research in Ann Arbor, Mich., says the federal government has said it intends to give a credit for stop-start systems in the 2017-25 rules.

That makes sense. After all, automakers get credits for using greener air-conditioning systems. Why not add a few mpg to the CAFE score of a vehicle with stop-start?