An RDE is theoretically more efficient than conventional deflagrative combustion by as much as 25%. The concept has been known for some time but is finally making progress due to new materials/modeling.

Sources & Credits:
ICE
   • Image of a hydrogen engine  
   • Achates Power Opposed-Piston Engine  
   • Bourke 10 CID engine exploded!!!  

Pulse Detonation
   • ACEL Pulse Detonation Engine (PDE)  
   • Penn State Altoona Pulse Detonation E...  
   • Valveless Pulse Detonation Engine  

RDE
   • Rotating detonation engine  
   • Longitudinal pulsations in Rotating D...  
   • Progress in RDC/Fortschritt bei der R...  
https://www.nasa.gov/centers/marshall...