Fleet Tests To Determine The Octane Response At Different Altitudes For Vehicles Equipped With Knock Sensors

Modern vehicles that are equipped with knock sensors do not have a clearly defined ‘octane requirement’ and very little research data has been published that demonstrates how such vehicles respond to altitude. An octane/altitude study was therefore carried out in South Africa during July 2002, involving 21 vehicles. Six fuels, ranging in octane from 89 research octane number (RON) to 102 RON were investigated and the tests were conducted at two locations having altitudes of 420 meters and 1485 meters. The engine torque was inferred from the vehicle acceleration on a chassis dynamometer and also by direct power measurement. Analysis of the test results revealed that the traditional “hockey-stick” response curve is an inappropriate model for the analysis of such vehicles. An ignition-timing/torque model provided a much-improved correlation and this enabled the effect of altitude to be identified in terms of octane-response equivalence.