Ars Technica: The US Navy currently spends approximately $2 billion per year on fuel for gas turbine engines in its ships and aircraft. Gas turbines are already highly optimized, so to meet its goals of increasing engine power levels by 10% and reducing fuel consumption by 25%, the navy is looking at alternative designs. The Naval Research Laboratory is working on rotating detonation engines (RDEs), a variation on pulse detonation engines (PDEs) that have been developed over the past 20 years. In an RDE, a series of micro-injectors pump a fuel–air mixture into a long ring-shaped combustion chamber in a sequential, circular manner. When the detonation is initiated, the resulting shock wave ignites each injection of fuel in turn, rotating its way around the chamber. The hot exhaust gases are forced by the shock wave to expand out of the cylinder and are expelled through a nozzle, which generates thrust. RDEs are still very experimental, but navy scientists have run simulations that show potential efficiencies of 85–89% of an ideal detonation cycle.