Ehson F. Nasir

Ultra-fast and calibration-free temperature sensing in the intrapulse mode

A simultaneously time-resolved and calibration-free sensor has been demonstrated to measure temperature at the nanosecond timescale at repetition rates of 1.0 MHz. The sensor benefits from relying on a single laser, is intuitive and straightforward to implement, and can sweep across spectral ranges in excess of 1  cm⁻¹. The sensor can fully resolve rovibrational features of the CO molecule, native to combustion environments, in the mid-infrared range near λ=4.85  μm at typical combustion temperatures (800-2500 K) and pressures (1-3 atm). All of this is possible through the exploitation of chirp in a quantum cascade laser, operating at a duty cycle of 50%, and by using high bandwidth (500 MHz) photodetection. Here, we showcase uncluttered, spectrally-pure Voigt profile fitting with accompanying peak SNRs of 150, resulting in a typical temperature precision of 0.9% (1σ) at an effective time-resolution of 1.0 MHz. Our sensor is applicable to other species, and can be integrated into commercial technologies.

A Shock-Tube Study of the CO + OH Reaction Near the Low-Pressure Limit

Rate coefficients for the reaction between carbon monoxide and hydroxyl radical were measured behind reflected shock waves over 700-1230 K and 1.2-9.8 bar. The temperature/pressure conditions correspond to the predicted low-pressure limit of this reaction, where the channel leading to carbon dioxide formation is dominant. The reaction rate coefficients were inferred by measuring the formation of carbon dioxide using quantum cascade laser absorption near 4.2 μm. Experiments were performed under pseudo-first-order conditions with tert-butyl hydroperoxide (TBHP) as the OH precursor. Using ultraviolet laser absorption by OH radicals, the TBHP decomposition rate was measured to quantify potential facility effects under extremely dilute conditions used here. The measured CO + OH rate coefficients are provided in Arrhenius form for three different pressure ranges: kCO+OH(1.2-1.6 bar) = (9.14 ± 2.17) × 10(-13) exp(-(1265 ± 190)/T) cm(3) molecule(-1) s(-1); kCO+OH(4.3-5.1 bar) = (8.70 ± 0.84) × 10(-13) exp(-(1156 ± 83)/T) cm(3) molecule(-1) s(-1); and kCO+OH(9.6-9.8 bar) = (7.48 ± 1.92) × 10(-13) exp(-(929 ± 192)/T) cm(3) molecule(-1) s(-1). The measured rate coefficients are found to be lower than the master equation modeling results by Weston et al. [J. Phys. Chem. A, 2013, 117, 821] at 819 K and in closer agreement with the expression provided by Joshi and Wang [Int. J. Chem. Kinet., 2006, 38, 57].

Calibration-Free and Ultra-Fast Sensing of Temperature and Species in the Intrapulse Mode

A new approach to measuring temperature, in which calibration-free and high timeresolution character are simultaneously achieved, is exploited through the use of intrapulse spectroscopy. The method promises to overcome uncertainties resulting from laser instability in using conventional fixed wavelength techniques.

Temperature Sensor for RCM Studies Based on Intrapulse Absorption Spectroscopy

A temperature sensor has been developed using two-line thermometry with QCLs in the intrapulse mode. The sensor has been demonstrated in high pressure environments at high bandwidth (100 kHz) in a Rapid Compression Machine (RCM).