Researchers at the University of Samara in the Lower Volga region are working on new power systems that use nonconventional fuel, the Russian news daily Rossiyskaya Gazeta reported.

Their new cryogenic engine is expected to use liquid nitrogen or liquefied natural gas as fuel. The developers believe it’s an ideal engine to propel eco-friendly motor vehicles in protected natural reserves and also drones for a range of special operations.

With the system, drones could stay invisible for infrared tracking devices as they wouldn’t leave thermal traces in the sky—unlike the current drones that are propelled by internal combustion engines or electric motors. The new power system project may take three-to-four years to complete.

The scientists are currently testing one of the engine’s key components, a cryogenic fuel storage system, using their proprietary sensor- and valve-equipped vessel, said Dmitry Uglanov of the University of Samara’s Institute of Engines and Power Units.