What Are the Advantages of a Rotating Detonation Engine for Naval Ships?

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Rotating Detonation Engines (RDEs) show potential thermodynamic efficiencies, particularly at low compression ratios, where they may outperform traditional jet engines. At Mach 2, ideal specific impulse for H2-air mixtures is 8500s, but simulated values are around 5000s, indicating a 60% efficiency of ideal. The efficiency of RDEs compared to diesel engines is debated, as RDEs experience losses from strong detonation shock waves, while diesel engines face weaker deflagration losses. However, RDEs may offer higher effective compression ratios, making them more efficient gas generators for naval applications. The Navy's interest in RDEs likely stems from their potential advantages over existing propulsion systems.
yangshi
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Just trying to understand how efficient RDE's are thermodynamically based on a 2016 paper from Bulat and Volkov titled "Detonation Jet Engine. Part 1 – Thermodynamic Cycle" and a 2013 paper by Nordeen et. al. titled "Thermodynamic Model of a Rotating Detonation Engine":

Based on these papers, at Mach 2 (just before the detonation front?), ideal specific impulse for H2-air mixtures is 8500s (FJ detonation cycle) while simulated impulse is ~5000s or 60% of ideal. Fig. 4 of the first paper shows thermodynamic conversion coefficient (assuming this is efficiency) vs. compression ratio b/w an FJ and Brayton cycle.

Assuming that specific impulse is proportional to efficiency and that jet engine efficiency is 90% of that of the ideal Brayton cycle (turbofan), one could conclude that at CR>10-ish, an actual jet engine would have higher thermodynamic efficiency than an actual RDE. For all other scenarios (engines with low compression ratios or that sacrifice efficiency for speed), an RDE can be more efficient?

Also, from http://physicstoday.scitation.org/do/10.1063/PT.5.026505/full/, why would the Navy want to replace their ship engines (assuming diesel engines) with RDEs since RDEs have efficiency loss from the strong detonation shock wave while diesel engines only have efficiency loss from a weaker deflagration wave? Is the FJ detonation cycle just more efficient overall than the diesel cycle?

I asked my combustion advisor this, and he was confused too. Any explanation would be appreciated. Happy holidays!
 
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yangshi said:
why would the Navy want to replace their ship engines (assuming diesel engines) with RDEs since RDEs have efficiency loss from the strong detonation shock wave while diesel engines only have efficiency loss from a weaker deflagration wave?
Ships now use gas turbines for propulsive power. This will increase as electrical generators, motors and controls become more common.

If you consider that efficiency is a function of compression ratio, then the detonation provides an effective higher compression ratio. I believe the RDE is a more efficient gas generator and that it can replace the combustor(s) in a gas turbine engine.
 

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