The knock resistance of gasoline is a key factor to decrease the specific fuel consumption and CO2 emissions of modern turbocharged spark ignition engines. For this purpose, high RON and octane sensitivity (S) are needed.
This study shows a relevant synergistic effect on RON and S when formulating a fuel with isooctane, cyclopentane and aromatics, the mixtures reaching RON levels well beyond the ones of individual components. The same is observed when measuring their knock resistance on a boosted single cylinder engine.
The mixtures were also characterized on a rapid compression machine at 700 K and 850 K, a shock tube at 1000 K, an instrumented and an adapted CFR engine. The components responsible for the synergistic effects are thus identified. Furthermore, the correlations plotted between these experiments results disclose our current understanding on the origin of these synergistic effects.
This study concludes that this synergistic effect encourages formulating highly paraffinic fuels for lower specific fuel consumptions and CO2 emissions. Thus, paraffins are still relevant compounds to formulate highly efficient gasolines, despite their low octane sensitivity when individually considered. Furthermore, the CFR engine is still the best known device to anticipate synergistic effects in gasoline's knock resistance, through the Octane Index (OI = RON - K.S). A sensitivity study on the “K value” of the octane index shows that octane sensitivity mainly drives the gasoline performance for the low-sensitivity fuels while RON also drives it for the high-sensitivity ones.