Effects of octane number on exhaust emissions of a spark ignition engine

This paper deals with the experimental study that aims to examine the effects of octane number of three different fuel oxygenates on exhaust emissions of a typical spark ignition engine. Three commonly used oxygenates, namely methyl tertiary butyl ether (MTBE), methanol, and ethanol, which were blended with a base unleaded fuel in three ratios (10, 15 and 20 vol%), were investigated. The engine emissions of CO, HC, and NO_x were measured under a variety of engine operating conditions using an engine dynamometer set-up. It is found that generally as the octane number of the fuel increases the CO and HC emissions decrease but the NO_x emission increases for all three blends. Further, for the leaded fuel (RON of 92), as the speed of the engine increases the CO and NO_x emissions decrease but the HC emission decreases. A similar trend was found for MTBE blends also. These emission results are presented in terms of octane number and their effects are discussed in this paper.