Methodology for Determining Octane Response at Different Altitudes for Vehicles Equipped with Knock Sensors

Road testing to determine the altitude/octane sensitivity of fuels and vehicles has traditionally been conducted according to the CRC E-15 method, which is based on the detection of audible knock. With the introduction of knock-sensors on modern engines, this method is no longer considered to be appropriate or viable. Acceleration-based methods have been proposed as an alternative technique for octane-requirement evaluation but, in terms of altitude-effect investigations, such methods are subject to the complexities of air density variations and its impact on overall vehicle acceleration. The present paper explores a more fundamental approach by extending the acceleration concept to its logical conclusion and deducing the underlying engine torque curve. This approach revealed the activity of the knock sensor directly in terms of its influence on the engine torque and it was concluded that the method represents an eminently suitable technique for altitude/octane evaluation. Accurate measurement of the vehicles acceleration was critical to the success of the method and was facilitated by the used of modern GPS technology.