Intra-pulse H2O absorption diagnostic for temperature sensing in a rapid compression machine

Abstract

An in-situ temperature diagnostic based on intra-pulse absorption spectroscopy has been developed using two pulsed quantum cascade lasers (QCLs) centered at 5.46 and 5.60 µm for rapid compression machine (RCM) experiments. Pulsed mode operation of the QCLs yielded a broad spectral tuning range (1.8-2.3 cm-1), through which spectral line-shapes of two H 2 O ro-vibrational transitions were resolved at high pressure conditions in the RCM (15-20 bar). Based on the resolved line-shapes, a calibration-free two-line thermometry method was used to determine the gas temperature. A high temporal resolution of 10 µs was achieved through a pulse repetition frequency of 100 kHz. The diagnostic was validated through measurements of temperature rise during the first-stage ignition of n-pentane/air mixtures. Thereafter, temperature rise during the first-stage ignition of iso-octane/air mixtures was quantified for the first time and compared with the calculated temperature rise using a chemical kinetic model.

Perspectives on instrumentation development for chemical species tomography in reactive-flow diagnosis

“…Assisted by bias-tee circuitry, diplexed radio frequency (RF) wavelength scan signals were imposed on continuous-wave distributed-feedback QCLs to measure line-of-sight thermodynamic and thermochemical properties at MHz rates [79][80][81][82]. When imposing long pulses on the QCLs, the down-chirp induced intrapulse spectra have been used for rapid sensing of temperature and species concentration [104][105][106][107]. The pulse repetition rates reported in the literature are generally limited to a few hundred kHz, due to spectral distortion at higher rates.…”

Laser Absorption

“…The line strength depends only on the temperature and is independent of pressure, species concentration, and path length. Therefore, gas temperature can be determined by measuring the ratio of integrated absorbance areas of a line pair as shown in the following expression [37]:…”

Stability Analysis of the Fluorescent Tracer 1-Methylnaphthalene for IC Engine Applications by Supercontinuum Laser Absorption Spectroscopy

“…Laser absorption spectroscopy is a well-established non-intrusive method for measuring mole fractions of different species (X i ), temperature (T), and pressure (p) within many applications [16][17][18]. Even under harsh conditions in combustion applications, e.g., in IC engines or Rapid Compression Machines (RCM), with rapidly changing temperature and pressure, various strategies exist for (multi-) parameter determination based on water absorption [18][19][20][21][22][23]. For the presented H 2 O mole fraction (X H2O ) measurements in the calibration cell, a broadband SCLAS high-speed NIR spectrometer is used and data analysis is performed by a Voigt line-shape absorption model that is based on the HITEMP database [24][25][26].…”