Performance Enhancement of a Small Two-Stroke Engine Using Nitromethane Blends

Increasing demand for unmanned aerial vehicles (UAVs) calls for a better understanding of its propulsion system. The present study characterizes a small two-stroke glow plug engine for up to 10 kg class of UAVs. To enhance the specific power output of the engine, nitromethane was used as a fuel additive. Understanding the effect of nitromethane concentration on the engine characteristics is the key objective of this present study. An engine test rig has been built to test a small two-stroke engine. The engine was run at various equivalence ratios. Engine characteristics such as thrust, RPM, torque, power, brake-specific fuel consumption (BSFC), and brake thermal efficiency (BTE) have been measured and compared with the base methanol fuelled engine. The results show around a 24% rise in the engine thrust with 40% (by mass) of nitromethane addition to methanol fuel. Energy balance analysis was carried out to show that the increased thrust is due to enhanced combustion efficiency with nitromethane addition. Hence, it is proposed that nitromethane blends can be used in short bursts whenever a large thrust is required by the UAV.