Quantifying Combustion Efficiency in Rotating Detonation Engines Using MHz-Rate Scanned-Wavelength-Modulation Spectroscopy

This work presents a framework to obtain reference-free combustion efficiency measurements in rotating detonation engines using a chemical balance model and a time-averaged \(\mathrm{H_2O}\) mole fraction. Because a time-resolved pressure measurement was not available, a new post-processing method was developed to estimate a time-averaged \(\mathrm{H_2O}\) mole fraction directly from time-resolved partial pressure measurements. The approach is demonstrated in an RDE with a 50% converging exit nozzle. Temperature and \(P_\mathrm{H_2O}\) were measured in-situ at 1 MHz using a single-ended scanned-wavelength-modulation spectroscopy sensor. Results across a range of equivalence ratios (\(\Phi \approx\) 0.5 - 1.5) and mass flowrates (150–350 g/s) showed combustion efficiencies of 50–65%, with uncertainties between 14–16% for most cases. Clear trends were identified between combustion efficiency, equivalence ratio, and wave speed ratios (\(\mathrm{D/D_{CJ}}\)). This framework enables accurate characterization of energy conversion losses in RDEs and supports future performance optimization.

Recommended citation: Guerrero, Jose, and Mirko Gamba. "Quantifying Combustion Efficiency in Rotating Detonation Engines Using MHz-Rate Scanned-Wavelength-Modulation Spectroscopy." Combustion and Flame (2026)
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