Reducing the greenhouse gases released from the production and burning of fuels like diesel and gasoline is a huge challenge facing the transportation industry.
Aamir Farooq and colleagues from KAUST's Clean Combustion Research Centre (CCRC), working with the Fuel Technology Team at Saudi Aramco, used an innovative technique for testing the properties of light naphtha, a fully blended, low-octane, highly paraffinic fuel. Farooq explains that this technique could open the potential for more advanced engines to run on fuels that release fewer emissions.
“Optimising fuel performance and engine designs must go hand-in-hand if we want to reduce emissions and improve engine efficiencies,” said Farooq. “Although gasoline and diesel engines have their advantages, we need a new type of engine that utilises the strengths, while avoiding the drawbacks, of current engine technologies.”
Diesel and gasoline engines, have fuel efficiencies of 35-40%. The new engine design, called a gasoline compression-ignition (GCI) engine, however, promises efficiencies of up to 55% as well as releasing fewer harmful soot and nitrogen oxides, compared with current engines.
But, realising these benefits requires a fuel with auto-ignition properties somewhere between gasoline and diesel.
“The auto-ignition properties determine the performance of the engine, and so has a significant influence on the engine’s design,” Farooq explained. “Like all fuels, light naphtha contains hundreds of compounds, so to perform detailed engine optimisation we need a simpler model of the fuel, called a surrogate fuel.”
The researchers compared auto-ignition properties of light naphtha with two surrogates - a simple, primary reference fuel surrogate and a more complex surrogate - over a range of temperatures, pressures and fuel/air ratios. Operating at high temperatures, they first used a shock tube to study the auto-ignition behaviour of the surrogates over different pressures. However, at lower temperatures reactions take longer, so a rapid compression machine was used to extend the observation time for the reactions.
They found the complex surrogate almost perfectly matched the light naphtha, particularly at lower temperatures, providing a full picture of its auto-ignition characteristics.
“Our work has produced the first auto-ignition model for light naphtha, and is being used by Saudi Aramco's Research Centre in Detroit to optimise GCI engine designs,” says Farooq.
