Argonne develops computer model to explore fuel octane number

Argonne develops computer model to explore fuel octane number

This large eddy simulation captures the start of knocking combustion in the CFR engine. The green iso-surface represents the corrugated turbulent flame front. Blue regions depict end-gas auto-ignition ahead of the flame. Velocity contours are shown on the horizontal cut plane.

The fuel and engine community has been using Cooperative Fuel Research (CFR) engines for nearly a century to quantify a fuel’s “knocking” propensity, or the likelihood that it will autoignite in the engine under typical operating conditions. But there is a lot behind this standardized test method for internal combustion engines that scientists don't yet understand.

That could soon change now that researchers at the Department of Energy’s (DOE) Argonne National Laboratory have developed a virtual model of the actual “hardware” CFR engine.

This new, three-dimensional engine simulation tool can help researchers probe how a fuel’s chemical kinetics translate into its octane rating.

Principal Computational Scientist Sibendu Som of Argonne’s Energy Systems division, along with postdoctoral appointee Pinaki Pal, have been collaborating with combustion research engineers Christopher Kolodziej and Toby Rockstroh, on the project for two years. This past April, they presented their work at the Society of Automotive Engineers (SAE) World Congress in Detroit, shortly after their findings were published by the SAE as a technical paper titled “Development of a virtual CFR engine model for knocking combustion analysis.”

Their project is part of a broader DOE initiative called the Co-Optimization of Fuels and Engines, or Co-Optima, which is co-funded by the Bioenergy Technologies Office and the Vehicle Technologies Office of the DOE’s Office of Energy Efficiency and Renewable Energy.

Co-Optima aims to simultaneously transform both transportation fuels and vehicles, helping researchers identify and develop engines designed to run more efficiently on affordable, scalable and sustainable fuels.

Pinaki Pal’s modeling work and the experimental campaign led by Christopher Kolodziej, highlight the value of both hardware and virtual experimentation — and how each is augmented by the other.

Engine “knocking” signals abnormal combustion, caused by violent chemical reactions and pressure dynamics that can damage critical engine components such as the cylinder head and pistons.

A fuel’s knock resistance is reflected in its octane rating, characterized at local gasoline stations by a pump octane number of 87, 89 or 91-93. If the number is high, the fuel is less likely to autoignite or knock during combustion, but these values are becoming less predictive for modern downsized boosted spark-ignition engines.

“There is a lot that needs to be better understood about how the physical and chemical properties of fuel affect the actual operating conditions and combustion characteristics of the CFR engine during octane testing,” Kolodziej said. “You can have fuels with the same octane rating but different knock characteristics. Advanced simulations give us the capability to model parameters simply not possible to measure in the real engine without affecting what’s being measured.”

With the new model, researchers can begin computerized experiments using any fuel they like.

“We can come up with new fuel formulations and readily assess their performance using simulations,” Pal said.

Now is the time to take action, he added. A better understanding of fuel octane rating, Pal said, “is crucial to improving the efficiency of modern boosted engines and designing novel fuels to reduce petroleum consumption and emissions.” Improved fuel efficiency benefits national security, domestic competitiveness and eases the burden on the household wallet.

The researchers used Argonne’s Laboratory Computing Resource Center and the HPC center at the DOE’s National Renewable Energy Laboratory.
DOE’s Office of Energy Efficiency and Renewable Energy supports early-stage research and development of energy efficiency and renewable energy technologies that make energy more affordable and strengthen the reliability, resilience, and security of the U.S. electric grid.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website.