Intracavity absorption spectroscopy of formaldehyde from 6230 to 6420 cm−1

Abstract

In combustion processes, during ignition, part of the fuel is converted to CH 2 O before substantial heat release. The complex chemical interaction of CH 2 O with oxidizer, fuel, and other intermediates determines the ignition delay time, i.e., the time between bringing the fuel/ oxidizer mixture into ignition conditions (usually by compression) and its conversion into combustion products. Fundamental understanding of the chemical and physical processes responsible for ignition is essential for efficient and safe operation of combustion equipment. Usually, experimental studies of ignition processes are performed by measuring ignition delay times. However, the amount of detailed information derived from ignition delay times is very limited, and consequently, time-resolved studies of the ignition process are required for understanding the underlying physical/chemical processes. The comparison of measured temporal profiles of intermediate species (e.g., CH 2 O) with those calculated using detailed combustion mechanisms, is capable of providing insights into ignition processes and to verify and/or improve theoretical models. Laser-diagnostic techniques with high sensitivity and high sampling rates are required for this purpose. Although laser diagnostics of CH 2 O in combustion environments are relatively well established, none of the techniques usually applied is capable of fully satisfying the requirements posed by the harsh environment, the low species concentration, and the fast reaction rates.One of the most established laser-based methods for measuring CH 2 O in combustion environments is laserinduced fluorescence (LIF). It provides high sensitivity, together with high temporal and spatial resolution. LIF was successfully implemented for combustion diagnostics of CH 2 O in laminar and turbulent flames, flow reactors, and engines [1][2][3]. Unfortunately, this method is difficult to apply for quantitative diagnostics because of substantial Abstract We apply intracavity absorption spectroscopy for measurements of the absorption spectrum of formaldehyde, CH 2 O, from 6230 to 6420 cm −1 , of which only a small fraction (6351-6362 cm −1 ) has been recorded elsewhere. The measurements are performed in the cavity of a broadband Er 3+ -doped fiber laser, with a sensitivity corresponding to the effective absorption path length of 45 m and a spectral resolution of 0.1 cm −1 . The noise-equivalent detection limit of CH 2 O achieved with the strongest absorption line at 6252.64 cm −1 is estimated to be 5 ppm. High tolerance to broadband losses and the accessible time resolution of 50 µs make it possible to apply this detection system for time-resolved monitoring of CH 2 O together with other molecules in harsh combustion environments, e.g., in combustion engines.

An improved rovibrational linelist of formaldehyde, \spec{h212c16o}

“…Range / cm −1 Reason for exclusion 17FjHeBaLe [28] 6230 -6240 700 K emission spectrum, line parameters not provided 15RuHeHeFi [105] 6547 -7051 No line assignments 09PeJaTcLa [101] 1600 -3200 Calculated line positions only 07ZhGaDeHu [98] 6351 -6362 No line assignments 06FlLaSaSh [94] 3096 -5263 Data not made available by the authors 06PeVaDa [95] 2600 -3100 No line parameters provided, data not made available by the authors 05StGaVeRu [93] 6547 -6804 No line assignments 03PeKeFl [92] 1000 -2000 Data not made available by the authors 02BaCoHaPe [90] 5600 -5700 Data analysed by 07SaBaHaRi [99] 96BoHaGrSt [88] -Dispersed fluorescence, vibrational state data only 96LuCoFrCr [89] 7800 -15200 No line parameters provided 89ReNaDaJo [83] 890 -1590 No line parameters provided 87NaDaRe [81] 1148 -1193 Lines included in 88NaReDaJo [87] 78Pine [73] 2700 -3000 No line parameters provided 75Nerf [66] 1 -10 Lines are given in 72Nerf [60] 73JoMc [64] 1707 -1767 No line parameters provided 70TuThTo [56] 0.15 -0.15 Line is given in 71TuToTh [58] 60OkHiSh [48] 0.98 Lines are given in 64OkTaMo [52] including this work, yielding 19 831 transitions, of which 16 596 are non-redundant.…”

“…Formaldehyde has been observed in different flames [26,27], most famously in cold flames, first by Sir Humphry Davy [26] in 1817. The spectrum of formaldehyde has been used for its timeresolved monitoring in combustion engines [28], for which supporting spectroscopic studies have been performed [29].…”

“…The importance of line-by-line information on formaldehyde has led to a large number of laboratory studies of its high-resolution rotational-vibrational spectra [10,28,, involving a diverse set of experimental techniques, such as SEP [10], dispersed laser-induced fluorescence [75], conventional infrared spectroscopy, with some of the oldest results contained in Refs. [54,57,65,67,68], tunable infrared difference frequency laser spectroscopy [74], and sub-Doppler laser Stark and Doppler-limited Fourier-transform spectroscopy [79].…”