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PPPL scientists find spinning gas in cylinders could improve the efficiency of engines while reducing pollutants

Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have received a patent from the US Patent and Trademark Office for a novel design that could increase the efficiency and reduce toxic emissions from gasoline-fueled internal combustion engines. The theoretical design lays out methods for rapidly spinning the gas inside engine cylinders.

In the patent, the design of the engine includes a main cylinder and main piston that are relatively axially displaceable along a main axis to define a variable volume main working chamber. At least one valve is configured to admit air and fuel into the working chamber forming an air/fuel mixture.

The main cylinder is configured to cause the air/fuel mixture in the main cylinder to spin rapidly enough to cause a substantive change in the heat capacity of the air/fuel mixture creating a spinning air/fuel mixture.

The main cylinder and main piston are configured to compress the spinning air/fuel mixture to create an ignitable spinning air/fuel mixture. The spinning air/fuel mixture is ignited and the main cylinder and main piston are configured to extract mechanical energy from the ignited spinning air/fuel mixture. An exhaust valve is configured to exhaust combustion products from the main working chamber.

The idea is to get net power out of engines working at lower temperature than otherwise thought possible and thereby reduce the emission of toxic nitrogen oxides.

—PPPL physicist Nat Fisch, Princeton Professor of Astrophysical Sciences, a co-developer of the patented method

Lead developer is physicist Vasily Geyko, who worked on the project as a graduate student in the Princeton Program in Plasma Physics at PPPL, which Fisch directs.

The patent, for which Fisch and Geyko initially applied in 2014, grew out of research the physicists were conducting on rapid spinning and compressing of plasma—the hot, charged soup of electrons and atomic nuclei—rather than gasoline. During the study, supported by the DOE’s National Nuclear Security Administration (NNSA) and the US Defense Threat Reduction Agency, the researchers discovered that rapidly rotating a neutral gas could produce conditions that benefit gasoline engines.

However, Geyko and Fisch discovered that the heat capacity of an ideal spinning gas—its ability to absorb energy while being heated—is greater than that of a stationary one. The scientists then realized that a gas rotating at roughly the speed of sound, when used in a thermodynamic cycle, could allow engines to operate at lower temperature more efficiently than conventional internal combustion engines.

Utilized for Otto or Diesel cycles, the heat capacity effect increases the thermodynamic efficiency for fixed maximum and minimum operating temperatures. Moreover, the relative efficiency gain is greater as maximum operating temperatures grow smaller. This makes the invention particularly beneficial for use in very low temperature engines.

—Vasily Geyko

The spinning gas also modifies the standard internal combustion engine design.

The invention features an eight-cycle engine, rather than a four-cycle engine, in order to spin the gas at the right points in the cycle. That complicates the engine of course. And a conventional engine will be more efficient at conventional temperatures.

But at very low temperatures, where conventional engines operate with very poor efficiency, the emission of poisonous nitrogen oxides from burning gasoline will be significantly less. At those temperatures our invention might be practiced to advantage, with higher efficiency and fuel economy, with corresponding public health benefits from improved air quality through the reduction of the nitrogen oxides emission.

—Nat Fisch

For now, the patented findings remain theoretical. But, for example, if Congress were to legislate a nationwide reduction in nitrogen oxides, the theoretical possibilities could become very much worth further development, Fisch said.

In principle, even a moderate reduction of allowed combustion temperatures, to around say 1,300-1,800 degrees Celsius from around 2,500 degrees Celsius, would be enough to achieve a relative efficiency advantage for a spinning gas-based engine of 5-to-10 percent as compared to a conventional Otto cycle engine.

—Vasily Geyko

PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas—ultra-hot, charged gases—and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the US Department of Energy’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States.




Well, many engines have had air swirl in the cylinder long before I was born. In fact, the trend has actually been to reduce swirl for many reasons. After a short glance, I cannot really comprehend how this invention could be used to improve engines, i.e. without introducing such serious drawbacks in other fields so that the net gain would become negligible.

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