With its strong dependence on gas-turbine engines for propulsion, the US Navy is looking to improve the fuel consumption of these engines. One potential method The US Naval Research Laboratory (NRL) is studying is the complex physics of Rotating Detonation Engines (RDEs), which offer savings by reducing fuel consumption in gas-turbine engines.
Many Navy aircraft use gas-turbine engines for propulsion, with the Navy's gas-turbine engines being fundamentally similar to engines used in commercial airplanes. The Navy also depends on gas-turbine engines to provide propulsion and electricity for many of its ships. Even as future ships move toward the model of an 'all electric' propulsion system, they will still need gas-turbine engines to produce electricity for the propulsion system and other critical systems. So building a gas-turbine engine that can handle the Navy's requirements for its warfighting ships and provide a fuel-efficient engine is a high priority.
The laboratory (with a complement of nearly 2,500 personnel, located in southwest Washington DC with other sites at the Stennis Space Center, Miss., and Monterey, Calif) say that the US Navy finds gas-turbine engines attractive because they scale nicely to large powers, are relatively small and self-contained, and are relatively easy to maintain. The gas-turbine engines the Navy uses today are based on the Brayton thermodynamic cycle, where air is compressed and mixed with fuel, combusted at a constant pressure, and expanded to do work for either generating electricity or for propulsion. To significantly improve the performance of gas-turbine engines, the navy researchers say they need to look beyond the Brayton cycle to explore alternative and possibly more innovative cycles.
One attractive possibility is to use the detonation cycle instead of the Brayton cycle for powering a gas-turbine. For the last decade NRL has been researching in this area and has been developing Pulse Detonation Engines (PDEs). NRL researchers estimate that retrofitting engines on existing Navy ships, like the USS Arleigh Burke , with rotating detonation technology could result in millions of dollars in savings a year..
The Rotating Detonation Engine (RDE) is an even more attractive and different strategy for using the detonation cycle to obtain better fuel efficiency. NRL researchers have constructed a model for simulating RDEs using earlier work done on general detonations, as a foundation.
Potential to meet 10% increased power requirements as well as 25% reduction in fuel use
NRL researchers believe that RDEs have the potential to meet 10% increased power requirements as well as 25% reduction in fuel use for future Navy applications. Currently there are about 430 gas turbine engines on 129 US Navy ships. These engines burn approximately $2 billion worth of fuel each year. By retrofitting these engines with the rotating detonation technology, researchers estimate that the Navy could save approximately $300 to $400 million a year.
Like PDEs, RDEs have the potential to be a disruptive technology that can significantly alter the fuel efficiency of ships and planes; however, there are several challenges that must be overcome.