Octane Response of Premium-Recommended Vehicles

A higher octane quality fuel used in premium-recommended vehicles has the potential for delivering better acceleration and power. Octane number is a standard measure for the anti-knock quality of a gasoline fuel. A higher octane number fuel can withstand more compression before detonation (or knock). Higher compression ratios directly correlate with engine power and thermodynamic efficiency. Hence engines that are designed for higher octane or premium grade fuels should typically develop higher power by extracting more from the calorific value of the fuel. However, in the case of premium-recommended vehicle models that are designed to run even on lower octane fuels, the extent of performance benefits of using premium grade higher octane fuels can be deciphered via vehicle testing. In this regard, two gasoline fuels with anti-knock index values (AKI) of 87 and 91 respectively were compared in five premium-recommended vehicles for acceleration and power benefits. The engines in these modern vehicles were equipped with knock sensors that signal the engine management system to retard the spark timing on knock detection and hence prevent knock. In principle, a lower octane quality fuel used in such engines may reduce the relative torque output and hence the performance of the engine. On the other hand, a higher octane fuel can be run at a higher ignition advance and result in higher torque values. The acceleration time and steady state power at wide open throttle conditions were recorded from chassis dynamometer tests. Data were analyzed and statistically assessed at 95% confidence level. The results indicated that some vehicles were more sensitive to octane quality in terms of changes in acceleration and power than others. On an average, 91 AKI fuel performed 1-2% better than the 87 AKI fuel.