E. Nasir, A. Farooq
Proceedings of the Combustion Institute, 36 (3), 4453-4460, (2017)
Rapid compression machine, Quantum cascade laser, Intrapulse, Absorption spectroscopy
A temperature sensor based on the intrapulse absorption spectroscopy technique has been developed to measure in situ temperature time-histories in a rapid compression machine (RCM). Two quantum-cascade lasers (QCLs) emitting near 4.55 µm and 4.89 µm were operated in pulsed mode, causing a frequency “down-chirp” across two ro-vibrational transitions of carbon monoxide. The down-chirp phenomenon resulted in large spectral tuning (Δν ∼ 2.8 cm−1) within a single pulse of each laser at a high pulse repetition frequency (100 kHz). The wide tuning range allowed the application of the two-line thermometry technique, thus making the sensor quantitative and calibration-free. The sensor was first tested in non-reactive CO-N2 gas mixtures in the RCM and then applied to cases of n-pentane oxidation. Experiments were carried out for end of compression (EOC) pressures and temperatures ranging 9.21–15.32 bar and 745–827 K, respectively. Measured EOC temperatures agreed with isentropic calculations within 5%. Temperature rise measured during the first-stage ignition of n-pentane is over-predicted by zero-dimensional kinetic simulations. This work presents, for the first time, highly time-resolved temperature measurements in reactive and non-reactive rapid compression machine experiments.