Raising the octane level of pump gasoline in the U.S. is integral to optimizing advanced combustion engines now in development, said GM and Honda executives at the 2016 CAR Management Briefing Seminars in Traverse City, MI. Their comments prompted positive but non-committal comments from Chris Grundler, Director of the Office of Transportation and Air Quality for the U.S. EPA.
During a panel discussion on future powertrains, Dan Nicholson, VP of Global Propulsion Systems at GM, and Robert Bienenfeld, Assistant VP of Environment and Energy Strategy at American Honda, agreed that the industry must push for a higher fuel-octane “floor” in the U.S.
“Higher octane fuels are the cheapest CO2 reduction on a well-to-wheels analysis,” Nicholson told panel moderator Brett Smith of CAR. “Fuels and engines must be designed as a total system. It makes absolutely no sense to have fuel out of the mix” of engine-technology discussions, he asserted.
Nicholson added that higher-octane, purpose-designed fuels “can be delivered very cost effectively.” A U.S. Dept. of Energy analysis proved the benefit of higher octane levels in improving combustion efficiency and reducing engine-out CO2, he said.
Honda’s Bienenfeld pointed out the benefits of higher fuel octane levels on advanced turbocharged engines operating under high-load conditions and in large-vehicle applications. He noted that boosted gas engines, hybrids and fuel-cell vehicles are on the future-development path at Honda. Nicholson touted the trend toward higher Otto cycle compression ratios and said his engineering teams are looking at Miller cycle combustion, in conjunction with turbocharging, “earning its way into the portfolio.”
Nicholson also said he’s bullish on diesels in the U.S., “which is one of the few growth markets” for compression-ignition engines, he stated.
Regarding 48-volt hybrids, Honda considers them to be cost effective “if the [current] standards stop at 2025,” Bienenfeld said.
EPA’s Grundler, speaking at MBS later in the day, noted that his agency is participating in the U.S. Dept. of Energy’s Optima project studying future fuels and has a working group focused on gasoline octane. “Fuel changes are not part of the TAR [Technology Assessment Report, part of the Mid-term Review of the current CAFE regulations],” he said, while suggesting that higher octane levels be considered for after 2025 “as long as increasing octane levels do not increase greenhouse-gas emissions.”
The Optima project aims at developing co-optimized fuels with a range of new engines for light-, medium-, and heavy vehicle use. Announced at the SAE High-Efficiency Engines Symposium by Dr. Wagner, Director of the Fuels, Engines, and Emissions Research Center at Oak Ridge National Laboratory, Optima is targeting a 30% reduction in petroleum consumption, per vehicle, compared with a projected 2030 base case that uses today’s fuels. The initiative is a collaboration with producers of gasoline and ethanol and the auto industry.
If Optima achieves its goal, it could reduce petroleum consumption by 4.5 billion barrels and save consumers up to $50 billion, according to the DoE.
Raising the U.S. octane “floor” will be essential for new combustion strategies currently in development for the 2020s including advanced Miller cycle and those combining lean-burn and stoichiometric operation aimed at achieving peak efficiency levels of 50%. and above. ORNL’s Dr. Wagner told the SAE audience that some multi-cylinder dyno engines have pushed beyond 55%.
Mazda’s Skyactiv program is progressing through G1, G2, and G3 development stages toward a marriage of Otto and Diesel cycle characteristics. Engineers’ target for the G3 is 18:1 compression ratio at lambda 2.5—a 40% improvement in thermal efficiency by setting the ideal pressure and temperature for homogeneous charge compression ignition (HCCI).
In Europe, the 102-RON (research octane number) “super premium” gasoline that’s widely available helps deliver a 10% increase in fuel efficiency for engines running compression ratios above 11.5:1, compared with engines running 9.0 to 9.5:1 using the 95-RON fuel that’s marketed as the mid-grade gas in Europe.