A TDLAS Temperature Sensor Up to MHz for Fast-Varying Transient Flows

A fast tunable diode laser absorption spectroscopy (TDLAS) sensor is proposed for gas temperature measurement in transient flows of a scramjet. Two distributed feedback (DFB) lasers emitting near 7185.58 and 7444.34 cm⁻¹ for H₂O detection were sinusoidally tuned to achieve two-line thermometry. Electro-optic modulators (EOMs) were used to perform envelope modulations for frequency division multiplexing and radiation noise immunity. A quantitative gas temperature uncertainty analysis model has been established for high-speed TDLAS sensors to optimize the tradeoff between accuracy and measurement speed of the sensor. The sensor rate was optimized to 1 MHz. The uncertainty model showed that a time resolution of 1 µs produced a temperature uncertainty of 8.8%, which was acceptable for monitoring high-frequency unstable combustion. Both simulation and experiments were conducted to evaluate the performance of the proposed sensor. In case of harsh scramjet exhaust flow, the proposed TDLAS sensor with a temperature range of 300–2200 K verified that the fluctuation frequency of exhaust flow was below 150 kHz. There is consistency between the uncertainty model and the sensor, with the faster the rate, the greater the deviation.