Researchers at KAUST, Saudi Aramco evaluating low-octane fuels for gasoline compression ignition engines
Gasoline compression ignition (GCI) is an experimental engine technology that could consume 25% less energy than a conventional automobile engine. (Earlier post.) GCI uses a gasoline-type fuel, but rather than ignited with a spark, it is compression-ignited like diesel. GCI engines operate at higher compression ratios than conventional gasiline engines, thus improving overall thermal eﬃciency. GCI could therefore be a best-of-both-worlds engine technology: combining the fuel efficiency of diesel engines with the low NOx and soot-particle emissions of gasoline.
Other studies have shown that GCI engines can operate with fuels with low octane numbers in the range of 50-70. The ability to use low-octane fuels would eliminate the need for the refinery catalytic reforming and isomerization units used to produce high-octane gasolines, thereby reducing costs and emissions. A collaboration between KAUST and Saudi Aramco scientists is now testing low-octane fuels for use in GCI engines.
At the Clean Combustion Research Center (CCRC) of King Abdullah University of Science and Technology (KAUST), significant efforts have been devoted towards formulating surrogates and developing combustion kinetics of gasolines with varying compositions and octane numbers.
… The current study aims to continue our efforts of formulating surrogates for wide variety of gasolines and improving the chemical kinetic modeling of these fuels. Specific objectives of the current study are two-fold; first, we aim to provide new ignition delay data for two low-octane FACE (Fuels for Advanced Combustion Engines) gasolines (FACE I and J); second, we wish to provide adequate surrogate formulation guidelines for such low-octane fuels. As mentioned earlier, ignition delay data are scarce for low-octane gasolines, and, hence, the data reported herein serves as valuable benchmark for future studies.—Javed et al.
The team focused on the chemical kinetics of auto-ignition of two low-octane gasolines with widely different compositions but similar octane ratings with anti-knock index, AKI = (RON + MON)/2, of ∼70 and sensitivity, S = RON–MON, of ∼3, said Tamour Javed, lead author. The team compared each low-octane gasoline with a potential two-component surrogate, measuring how closely its ignition behavior mimicked the real fuel.
The researchers measured the ignition delay times of the two low-octane fuels in a shock tube and a rapid compression machine over a broad range of engine-relevant conditions (650–1200 K, 20 and 40 bar and φ= 0.5 and 1). Experimental ignition delay time results showed that the two gasolines exhibited similar reactivity over a wide range of test conditions.
Furthermore, ignition delay times of a primary reference fuel (PRF) surrogate (n-heptane/iso-octane blend), having the same AKI as the FACE gasolines, captured the ignition behavior of these gasolines with some minor discrepancies s at low temperatures ( T < 700 K). Multi-component surrogates, formulated by matching the octane ratings and compositions of the two gasolines, emulated the autoignition behavior of gasolines from high to low temperatures.
Although it will take a significant update in refinery infrastructure to bring low-octane fuels to market, in the short-term, low-octane fuels could be made by combining conventional fuels, Aamir Farooq at KAUST’s Clean Combustion Research Center said. Studies to test the feasibility of mixing diesel and gasoline fuels to match the characteristics of a low-octane gasoline are underway at KAUST.
Javed, T., Ahmed, A., Lovisotto, L., Issayev, G., Badra, J. Sarathy, M.S., & Farooq, A. (2017) “Ignition studies of two low-octane gasolines.” 185, 152–159 doi: 10.1016/j.combustflame.2017.07.006