Oak Ridge National Laboratory engineers are trying to improve efficiency and performance in tiny engines in remote-controlled airplanes that have applications for aerial military surveillance.
Because UAVs are not burdened with the physiological limitations of human pilots, they can be designed for maximized on-station times. The maximum flight duration of unmanned aerial vehicles varies widely. Internal combustion engine aircraft endurance depends strongly on the percentage of fuel burned as a fraction of total weight and so is largely independent of aircraft size.
“Right now these engines are extremely inefficient,” said Mike Kass, senior engineer in ORNL’s Fuels, Emissions and Engines Group. “When you look at the energy density of a hydro-carbon fuel, it is quite high—roughly 45 times higher than the best lithium batteries. If you can improve the efficiency to as much as 10 percent, you’ve still doubled your fuel efficiency.”
One finding is that a titanium engine is more efficient than aluminum.
“The titanium head allows us to run under leaner conditions than can be achieved with the aluminum head because we’re getting a little more complete combustion,” Kass said. “The other thing that titanium allows us to do that we can’t with aluminum is that it is also a stronger higher temperature material, as well.”