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Many of the engines used in Remotely Piloted Aircraft (RPA), come directly from the remote-control (R/C) aircraft market, which turn a propeller but are not necessarily built for the greatest efficiency or reduced fuel consumption. The DoD “single fuel concept” is pushing these platforms to be able to operate with JP-8 using an Otto Cycle engine. Additionally, with increased environmental concern with fossil fuels, possible future DoD requirements could require the use of bio-derived liquid fuels. The research presented in this paper takes steps to satisfying both the efficiency and single fuel requirements. The Fuji BF-34EI engine was successfully shown to operate effectively with JP-8, Diesel, Algae-based Diesel and Camelina based Hydroprocessed Renewable Jet fuel. When generally compared over the entire engine operating map, between AVGAS and JP-8, the latter is shown to present a 10-20% lower brake specific fuel consumption (BSFC).

Small internal combustion engines (ICEs), (<7.5 kW), possess low thermal efficiencies due to high thermal losses. As the surface area to volume ratio increases beyond 1.5 cm2/cc, the increase in thermal losses leads to a drop off of engine efficiency and power. This effort describes the development and validation of a test stand to characterize thermal losses of small ICEs, optimize combustion phasing, and eventually enable heavy fuel operation. The test stand measures torque, rotational speed, brake power, intake air mass flow, up to 48 temperatures (including ambient, intake, cylinder head, fuel, and exhaust), 8 pressures (including ambient, intake, and exhaust), throttle position, and fuel and air mass flows. Intake air temperature and cylinder head temperature are controlled and adjustable. Three geometrically similar engines with surface area to volume ratios near 1.5 cm2/cc were selected from 3W Modellmotoren.