The Effects of Varied Octane Rating on a Small Spark Ignition Internal Combustion Engine

With the sustained interest in Unmanned Aircraft Systems (UAS) and Micro Air Vehicles (MAV), the military services have a real need for vehicles powered by an internal combustion (IC) engine that can run efficiently on heavy hydrocarbon fuels, especially JP-8 due to established logistics. This paper will discuss the results of running a 2 horsepower, 4- stroke, spark-ignition engine (FUJI BF34-EI) with both iso-Octane and n-Heptane. The two main topics that are addressed are the knocking characteristic of this engine with n-Heptane and a comparison of the brake specific fuel consumption (BSFC) between the two fuels. It is shown with stock timing and fuel at ambient temperature that n-Heptane exhibits on average 4.1% less specific fuel consumption than iso-Octane. Additionally, it can be concluded that the knocking characteristic of a zero octane number (ON) fuel in this engine is negligible, thus allowing the USAF to run any ON fuel for this particular engine.