Time-resolved temperature measurements in a rapid compression machine using quantum cascade laser absorption in the intrapulse mode

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 mu m and 4.89 mu m were operated in pulsed mode, causing a frequency "downchirp" across two ro-vibrational transitions of carbon monoxide. The down-chirp phenomenon resulted in large spectral tuning (Delta nu similar to 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-N-2 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. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.