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NRL's model of a Rotating Detonation Engine  (Source: nrl.navy.mil)
Currently, the Navy has 129 ships with 430 gas-turbine engines that burn $2 billion of fuel annually

The U.S. Navy is working on new technology for its gas-turbine engines in order to decrease fuel consumption without sacrificing performance.

The answer, according to the Naval Research Laboratory (NRL), is equipping current gas-turbine engines with Rotating Detonation Engine (RDE) technology. These engines could not only efficiently provide propulsion for Navy planes and ships, but also create electricity for an all-electric propulsion system.

The Navy currently uses gas-turbine engines that are based on the Brayton thermodynamic cycle, where air is compressed, combined with fuel, combusted at a constant pressure and expanded. This allows for propulsion or generating electricity, just like the RDEs. However, the Brayton cycle is less efficient than the detonation cycle.

Dr. Kazhikathra Kailasanath, head of NRL's Laboratories for Computational Physics and Fluid Dynamics, noted the following in a 2011 paper for the NRL Review:

The challenge with detonation engines is realizing the efficiency of the detonation cycle. Concepts such as oblique detonation-wave engines have failed to be able to recover the efficiency of this detonation cycle, because much of the energy of the inflow is bound up in kinetic energy, which does not increase the pressure and thus does not improve the efficiency. Pulse detonation engines have taken a different approach by creating an unsteady process that removes the requirement of having high velocity inflow. This creates a whole new set of issues, such as rapid initiation of detonations and the requirement of efficient detonators.

The rotating detonation engine takes a different approach toward realizing the efficiency of the detonation cycle. By allowing the detonation to propagate azimuthally around an annular combustion chamber, the kinetic energy of the inflow can be held to a relatively low value, and thus the RDE can use most of the compression for gains in efficiency, while the flow field matches the steady detonation cycle closely.

Currently, the Navy has 129 ships with 430 gas-turbine engines that burn $2 billion of fuel annually. By equipping engines with RDE technology, power could be increased by 10 percent while fuel consumption would decrease by 25 percent. The Navy could also save $300-$400 million annually.

Source: U.S. Navy



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RE: Why not clean coal?
By Solandri on 11/3/2012 11:55:36 AM , Rating: 5
Coal (bituminous in the below chart) has lower energy density by volume and weight compared to diesel, gasoline, and kerosene (aviation fuel).
http://upload.wikimedia.org/wikipedia/commons/c/c6...

That means for the same amount of fuel storage space, a coal-powered ship will have less range. And even if you could somehow compress the coal so it hypothetically gave the same range for the same volume of fuel, it would weigh substantially more. The ship would sit lower in the water and consume more fuel per distance traveled, and thus still have less range.


RE: Why not clean coal?
By EricMartello on 11/3/12, Rating: -1
RE: Why not clean coal?
By Fritzr on 11/3/2012 11:48:27 PM , Rating: 4
Coal is a tried fuel that was replaced by oil for safety reasons.

Remember the Maine... One of the scenarios that is supported by investigations of the sinking is a coal fire that set off munitions.

Coal self ignites in storage and fuel fires are taken for granted by coal fired ships and anyone else storing large amounts of coal.

Here is a link to a discussion thread with a great deal of information contributed by people who have first hand experience with coal power.
http://www.practicalmachinist.com/vb/antique-machi...


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