Simultaneous Mach number, thrust, and combustion efficiency measurement for a scramjet by using a beam-jitter-resistant TDLAS sensor

Scramjets are the optimal propulsion systems for hypersonic applications due to their air-breathing architecture. The Mach number, thrust, and combustion efficiency of a scramjet are very sensitive to parameter changes in the chamber and must be precisely measured using a non-contact experimental method, i.e., tunable diode laser absorption spectroscopy (TDLAS). The supersonic flow generated by the scramjet induces laser beam jitter in the TDLAS sensor. In this paper, a robust TDLAS sensor with beam-jitter-resistant capabilities was developed to quantify simultaneously temperature, pressure, H₂O concentration, and speed of supersonic flows in scramjets. From these four parameters, an online evaluation method for Mach number, thrust, and combustion efficiency was validated on a direct-connected scramjet platform. In supersonic flow, the signal-to-noise ratio of the proposed sensor was improved by approximately 9.28 dB. During stable operation, relative errors for average temperature, pressure, H₂O concentration, speed, Mach number, and thrust were respectively about 1.4 %, 3.4 %, 3.5 %, 0.4 %, 1.1 %, and 1.7 %. The combustion efficiency of the scramjet platform was 77.83 %. The proposed sensor enables the continuous monitoring of scramjet operation at an update rate of 5 kHz and provides an effective method for scramjet performance evaluation.