Absolute absorption cross sections for two selected lines of formaldehyde around 6625cm−1

Morajkar, Pranay P.; Schoemaecker, Coralie; Fittschen, Christa

doi:10.1016/j.jms.2012.10.004

Cited by 10 publications

(17 citation statements)

References 45 publications

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“…The spectra of C 2 H 4 , H 2 O and H 2 O 2 have been obtained during this work by flowing a diluted mixture of the species via the JSR at room temperature into the cw-CRDS cell: C 2 H 4 has been taken as a pure gas from a cylinder (99.95% purity, Air Liquide) and has been diluted with a known flow of Helium prior to entering the JSR, H 2 O has been obtained by bubbling a fraction of the He-flow through liquid water, H 2 O 2 has been obtained by bubbling through a solution of 50% H 2 O 2 / H 2 O and hence consists of the sum of both spectra, H 2 O and H 2 O 2 . The spectrum of CH 2 O has been taken from Staak et al 21 , however absolute absorption cross sections used in this work have been taken from Morajkar et al 22 . The absorption spectra for the individual species are relatively dense (except for H 2 O, which has well-defined and separated lines), and hence the spectrum of the gas mixture at the exit of the JSR, a convolution of the individual spectra weighted by the concentration of each species, is also very dense.…”

Section: Resultsmentioning

confidence: 99%

Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements

Bahrini

Morajkar

Schoemaecker

et al. 2013

Phys. Chem. Chem. Phys.

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The gas-phase oxidation of n-butane has been studied in an atmospheric jet-stirred reactor (JSR) at temperatures up to 950 K. For the first time, continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared has been used, together with gas chromatography (GC), to analyze the products formed during its oxidation. In addition to the quantification of formaldehyde and water, which is always difficult by GC, cw-CRDS allowed as well the quantification of hydrogen peroxide (H2O2). A comparison of the obtained mole fraction temperature profiles with simulations using a detailed gas-phase mechanism shows a good agreement at temperatures below 750 K, but an overestimation of the overall reactivity above this temperature. Also, a strong overestimation was found for the H2O2 mole fraction at higher temperatures. In order to improve the agreement between model and experimental results, two modifications have been implemented to the model: (a) the rate constant for the decomposition of H2O2 (+M) ↔ 2OH (+M) has been updated to the value recently proposed by Troe (Combust. Flame, 2011, 158, 594-601) and (b) a temperature dependent heterogeneous destruction of H2O2 on the hot reactor walls with assumed rate parameters has been added. The improvement (a) slows down the overall reactivity at higher temperatures, but has a negligible impact on the maximal H2O2 mole fraction. Improvement (b) has also a small impact on the overall reactivity at higher temperatures, but a large effect on the maximal H2O2 mole fraction. Both modifications lead to an improved agreement between model and experiment for the oxidation of n-butane in a JSR at temperatures above 750 K.

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Section: Resultsmentioning

confidence: 99%

Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements

Bahrini

Morajkar

Schoemaecker

et al. 2013

Phys. Chem. Chem. Phys.

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“…The excitation beam entered the cell through a quartz window, located at 90° with respect to the photolysis laser, and the fluorescence was collected at 90° with respect to the plane defined by the two laser beams. The principle has been described in detail in an earlier work and will not be repeated here.…”

Section: Methodsmentioning

confidence: 99%

“…Absolute concentrations of [HO 2 ] were determined from the known cross section of this absorption. Cw‐CRDS was also employed as a spectroscopic method, independent of laser photolysis, for the measurement of absolute CH 2 O concentrations present in the photolysis cell .…”

Section: Methodsmentioning

confidence: 99%

“…The amount of CH 2 O reaching the photolysis cell strongly depended on the temperature of the water bath: concentrations between 3 and 7 × 10 15 cm −3 were obtained by varying the bath temperature between 323 and 343 K. The CH 2 O concentration within the photolysis reactor was directly monitored by cw‐CRDS. We have recently measured absolute absorption cross sections for several lines of CH 2 O in the wavelength range near the current HO 2 absorption line . These measurements were based on measuring pseudo–first‐order decays of OH radicals in the presence of different concentrations of CH 2 O: From the well‐known rate constant of the reaction between CH 2 O and OH, the absolute concentration of CH 2 O can then be deduced.…”

Section: Methodsmentioning

confidence: 99%

“…Once the CH 2 O concentration within the reactor was stable, the concentration was determined by scanning the full absorption line. The absolute CH 2 O concentration within the reactor was determined from the known absorption cross section (2.47 × 10 −22 cm 2 at 50 Torr) .…”

Section: Methodsmentioning

confidence: 99%

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Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO₂ Radicals

Morajkar

Schoemaecker

Okumura

et al. 2013

Int J of Chemical Kinetics

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Rate and equilibrium constants for the reaction of HO2 with formaldehyde trueright130.79993pt CH 2normalO+ HO 2↔ HO CH 2O22.em2.em2.em2.em2.em2.em1em(normalR1) and acetaldehyde trueright118.79993pt CH 3 CHO + HO 2↔ CH 3 CH ( OH )O22.em2.em2.em2.em1em2.em(normalR2) have been directly measured. The concentration of HO2 radicals was followed in a time‐resolved method by coupling cw‐CRDS (cavity ringdown spectroscopy) to laser photolysis. The reaction of HO2 with CH2O (R1) was measured at 50 Torr helium over the temperature range 292–306 K, whereas the reaction of CH3CHO with HO2 (R2) was measured in 50 Torr He but at only 294 K. The observed HO2 decay profiles were modeled to take into account secondary chemistry, especially that of the reaction products, hydroxyl‐peroxy radical adducts. The rate constants for forward and back reactions of (R1) at 297 K were found to be k1 = (3.3 ± 0.6) × 10−14 cm3 molecule−1 s−1 and k−1 = (55 ± 5) s−1, respectively, both roughly a factor of two slower than earlier measurements (possibly due to falloff effects), while the equilibrium constant was found to be K1 = (6.0 ± 1.8) × 10−16 molecule−1 cm3 at 297 K, in good agreement with earlier, more indirect determinations. The equilibrium constant of the reaction with CH3CHO was found to be K2 = (1.7 ± 0.5) × 10−17 molecule−1 cm3 at 294 K, with the forward rate constant k2 = (1.5 ± 0.75) × 10−14 cm3 molecule−1 s−1 and the rate constant for the back reaction k−2 = (900 ± 450) s−1.

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Characterisation of DME-HCCI combustion cycles for formaldehyde and hydroxyl UV–vis absorption

Azimov

Stylianidis

Kawahara

et al. 2017

Fuel

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We investigated time-resolved ultraviolet-visible (UV-vis) light absorbance to identify the formation behaviour of formaldehyde (HCHO) and hydroxyl (OH) within the wavelength range of 280-400 nm in a homogeneous charge compression ignition (HCCI) engine fuelled with dimethyl ether (DME). The time-resolved HCHO and OH profiles at different initial pressures showed that HCHO absorbance increased in the lowtemperature reaction (LTR) and thermal-ignition preparation (TIP) regions and decreased gradually as the combustion approached the high-temperature reaction (HTR) region. At higher intake pressures, HCHO absorbance decreased and OH absorbance increased. The time-resolved absorbance spectra of HCHO, with peaks at 316, 328, 340, and 354 nm for all combustion cycles, were evaluated and it was found that average absorption at 328 nm was slightly higher than at 316, 340, and 354 nm. For knocking combustion cycles, the absorbance of HCHO in the LTR region was high for cycles with low knock intensity and low for cycles with high knock intensity, showing a high level of OH absorbance. Chemical kinetics analyses showed that for different fuel/oxidiser ratios, initial O2 concentration and intake temperature had no effect on in-cylinder temperatures in the LTR or TIP regions. However, they did have significant effects on HTR combustion. In-cylinder temperature in the LTR region had less effect on HCHO and H2O2 formation than pressure.  HCHO absorbance increased in LTR and TIP regions and decreased in HTR region  HCHO decreased as RoHR increased and vice versa  O 2 and intake temperature did not affect in-cylinder temperature in LTR and TIP  O 2 and intake temperature had significant effects on HTR combustion  HCHO concentration was very low when knock intensity was very high, and vice versa Highlights (for review) 2

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Absolute absorption cross sections for two selected lines of formaldehyde around 6625cm−1

Cited by 10 publications

References 45 publications

Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements

Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements

Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO₂ Radicals

Characterisation of DME-HCCI combustion cycles for formaldehyde and hydroxyl UV–vis absorption

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Absolute absorption cross sections for two selected lines of formaldehyde around 6625cm−1

Cited by 10 publications

References 45 publications

Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements

Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements

Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO2 Radicals

Characterisation of DME-HCCI combustion cycles for formaldehyde and hydroxyl UV–vis absorption

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Product

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Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO₂ Radicals