Impact of octane numbers on combustion performance and driving cycle fuel consumption of turbocharged direct-injection spark-ignition engine

The efficiency of modern spark-ignition engines is constrained by knock-limited combustion and hence the fuel's octane rating. This paper investigated the impact of the Research Octane Number (RON) and Motor Octane Number (MON) on the anti-knock performance in a 2.3-L gasoline turbocharged direct-injection (GTDI) engine and determined the octane impact on drive cycle fuel consumption of a conventional vehicle powered by this engine. Four fuels of different octane numbers were tested over the engine map at both normal and high intake temperatures: three fuels with varying MONs (81–86) at a constant RON (91), and a fourth fuel with a higher RON (95). The consumption of each fuel was calculated for standard EPA vehicle drive cycles and hot-weather towing tests. The engine results show that a higher RON consistently improves the engine's anti-knock performance and thermal efficiency at knock-limited conditions. The effect of the MON is more complex, in that higher MON improves the knock resistance at the lowest knock-limited loads and thus increases thermal efficiency, whereas a lower MON performs better at higher loads and at high intake temperature. Drive cycle analysis shows that increasing RON (91 to 95) and decreasing MON (86 to 81), separately reduce the fuel consumption by up to 10.8 and 4.5%, respectively, in hot-weather towing tests. By contrast, no noticeable change of fuel consumption is observed in the urban and highway driving cycles when using these test fuels.