Fuels for an experimental engine technology that could consume 25 percent less energy than a conventional automobile engine were evaluated by researchers from Saudi Aramco and King Abdullah University of Science and Technology (KAUST). A gasoline-type fuel is used in gasoline compression ignition (GCI), but ignition is not triggered by a spark. The engine is compression-ignited as in a diesel system, suggesting that GCI could beneficially combine the fuel efficiency of diesel engines with the low nitrogen oxides and soot-particle emissions of gasoline.

To help optimize engine design, the researchers analyzed the combustion chemistry of two low-octane Students test fuel ignition chemistry using two shock tubes at the KAUST Clean Combustion Research Center. Source: KAUSTStudents test fuel ignition chemistry using two shock tubes at the KAUST Clean Combustion Research Center. Source: KAUSTgasolines ignited under engine-relevant conditions. “Our focus was to probe the chemical kinetics of auto-ignition of two low-octane gasolines with widely different compositions but similar octane ratings,” says Tamour Javed, who worked on the project as part of his PhD research.

“To optimize the performance of GCI engines, we used high-fidelity predictive computer simulations,” explains Aamir Farooq of KAUST’s Clean Combustion Research Center. “A big part of such simulations is the description of fuel chemistry.” As a real gasoline fuel is too complex a chemical mixture to simulate, “… we try to formulate a simpler representation of the real fuel, known as a surrogate.”

Each low-octane gasoline was compared with a potential two-component surrogate to measure how closely its ignition behavior mimicked the real fuel. Under most conditions, the two-component surrogate proved to be a good representative of real low-octane fuel, its behavior only diverging at low ignition temperatures.

Major modifications in refinery infrastructure will be needed to bring low-octane fuels to market, but low-octane fuels could be made available in the near-term by combining conventional fuels. The researchers are now examining the feasibility of mixing diesel and gasoline fuels to match the characteristics of a low-octane gasoline.

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