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

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SUMMARY

The discussion centers on the thermodynamic efficiency of Rotating Detonation Engines (RDEs) for naval applications, referencing key papers by Bulat and Volkov (2016) and Nordeen et al. (2013). At Mach 2, the ideal specific impulse for H2-air mixtures is 8500 seconds, while simulated values reach approximately 5000 seconds, indicating a 60% efficiency of the ideal. The conversation suggests that RDEs may outperform traditional jet engines at low compression ratios, despite their inherent efficiency losses due to detonation shock waves. The Navy's interest in RDEs likely stems from their potential as more efficient gas generators compared to conventional diesel engines.

PREREQUISITES
  • Understanding of thermodynamic cycles, specifically FJ detonation and Brayton cycles.
  • Familiarity with specific impulse and its implications for engine efficiency.
  • Knowledge of gas turbine technology and its application in naval propulsion.
  • Basic principles of combustion and detonation dynamics.
NEXT STEPS
  • Research the thermodynamic models of Rotating Detonation Engines.
  • Study the implications of compression ratios on engine efficiency.
  • Explore advancements in gas turbine technology and their integration with RDEs.
  • Investigate the potential benefits of RDEs over traditional diesel engines in naval applications.
USEFUL FOR

Naval engineers, propulsion system designers, combustion researchers, and anyone interested in the future of marine engine technology.

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.