Abstract
KEYWORDS – HALE UAV (High Altitude Long Endurance Unmanned Aerial Vehicle), Gasoline Engine, 3-stage Turbocharger system, Gasoline Engine Simulation, Ricardo WAVE
ABSTRACT
A high altitude long endurance unmanned aerial vehicle (HALE UAV) is required to stay more than 30 hours at 20 km (60,000 ft) altitude. Various propulsion systems have been investigated for application in HALE UAV. Gasoline reciprocating engine is suitable for HALE UAV due to high technical maturity and high thermal efficiency. In this study, a simulation study was conducted with applying the specifications of a passenger car gasoline engine and a 3-stage turbocharger system for engine operation at the ambient conditions of 18 km altitude. The modeling and simulation were performed by Ricardo WAVE. The modeling and simulation of the gasoline engine was conducted with applying the specifications and geometry of a 2.4L 4-cylinder gasoline engine of a commercial car at room temperature and pressure conditions. The combustion duration in Wiebe combustion model was applied 30 CA (crank angle) of typical gasoline engines. CA50 (crank angle corresponding to 50% heat release) was set to MBT (Minimum advance for Best Torque). The intake/exhaust valve timings were also optimized for the maximum brake torque and power. 3-stage turbocharger and intercoolers were selected to pressurize and cool the ambient air of 18 km altitude to the pressure and temperature on the ground. The selected 3-stage turbocharger and intercoolers were added to the gasoline engine model and simulated at 18 km altitude environment. The simulation results of the naturally aspirated gasoline engine model were compared with the performance of the actual gasoline engine for ensuring the reliability of the simulation model and it showed up to 5.7% error. The minimum fuel consumption was achieved at the engine speed of 3,500 rpm in the gasoline engine with the selected 3-stage turbocharger. The maximum power was produced at 5,000 rpm. Moreover, the operating strategy of 3-stage turbocharged gasoline engine was established according to the height from ground to 18 km altitude. However, 3-stage turbocharged gasoline engine at 18 km altitude was not able to be driven at less than 3,000 rpm because of insufficient flow for the turbine of 3-stage turbocharger.