Impact of Octane Number on Fuel Efficiency of Modern Vehicles

Fuel quality, including antiknock rating, plays a critical role in enabling optimal operation of advanced gasoline engines. As new designs introduced into the market implement technologies to improve fuel efficiency, the overall octane level of the gasoline pool may need to be increased to ensure optimal performance. Turbocharging, higher compression ratios and downsized displacement all lead to higher combustion pressures and temperatures that make engines more susceptible to knocking. All modern gasoline engines are equipped with knock sensors that detect abnormal combustion resulting from autoignition caused by insufficient octane quality. The ability of an engine to account for the use of lower octane fuel by retarding spark timing and enriching air-fuel ratio to reduce knock is limited, and engine efficiency is directly and adversely impacted when the use of lower octane gasoline is accommodated, resulting in higher fuel consumption. In this paper, the impact of gasoline octane quality on the fuel efficiency of advanced vehicles in China is investigated. Five in-use vehicles equipped with various fuel efficient engine technologies were subject to fuel economy and emissions testing on multiple commercial fuels spanning the relevant range of octane quality for this market. Results demonstrated that the use of high octane gasoline consistently enabled advanced gasoline engines to achieve maximum energy savings in the form of approximately 1% better fuel economy per octane number increase.