A 120 kHz mid-infrared TDLAS sensor for combustion efficiency measurement in rotating detonation engines

The rotating detonation engine (RDE) stands out in the aerospace propulsion system owing to its high burn rate, exceptional thermal efficiency, and a compact design without large moving parts. This study presents a 120 kHz state-of-art mid-infrared tunable diode laser absorption spectroscopy (TDLAS) sensor to measure H₂O concentration, temperature, axial velocity, and combustion efficiency based on product mass-flow-rate in a hydrogen-fueled annular RDE. With an equivalence ratio of 0.8, results indicate a detonation wave propagating velocity of 1383 m/s, a mean temperature of 1532 K, a water partial pressure of 0.328 atm, an axial flow of 424 m/s, and a combustion efficiency of 79.6 %. Combustion analysis reveals that 41.4 % of the hydrogen undergoes Chapman–Jouguet detonation, 38.2 % undergoes deflagration and 20.4 % remains unburned. The developed high-speed diagnostic achieves temporal resolution commensurate with detonation timescales and establishes a novel framework for the in-situ qualification of chemical reaction progress in RDEs.