The Performance and Emissions Effects of Utilizing Heavy Fuels and Biodiesel in a Small Spark Ignition Internal Combustion Engine

Abstract

The Department of Defense has a sustained interest in the universal use of heavy, low volatility hydrocarbon fuels for safety and logistical reasons. There is also an increased environmental interest in lower emission, domestically grown biofuels. Many Remotely Piloted Aircraft (RPA) use small internal combustion engines for propulsion that are designed to run on high octane, highly volatile fuels. This paper discusses the experimental results of running a 4-stroke, spark ignition, 33.5 cc internal combustion engine with Avgas, JP-8 and Camelina Biofuel. Carburetor settings were unaltered and data is shown for two sets of engine loading points derived from torque requirements for cruise conditions with different fielded propeller load lines. Results show that for cruise points required torque output could be achieved with heavy fuels. Brake specific fuel consumption (bsfc) was lower for the heavy fuels, with JP-8 showing the lowest specific fuel consumption. Emissions data for the heavy fuels (compared to Avgas) shows lower CO and hydrocarbon emissions and higher CO2 and NOx emissions. If cold starting, fuel metering, and knocking issues can be resolved, preliminary results indicate heavy fuels can meet power requirements while lowering fuel consumption and CO/hydrocarbon emissions.