In-situ thermochemical analysis of hybrid rocket fuel oxidation via laser absorption tomography of $$\text {CO}$$, $$\text {CO}_{2}$$, and $$\text {H}_{2}\text {O}$$

Robust cepstral analysis at variable wavelength scan depth for narrowband tunable laser absorption spectroscopy

“…The average spread for m-FID is 0.27%, also smaller than the spread of 1.95% for DAS. Since larger offsets of the measured baseline associated with background thermal emission are commonly observed in practical environments, such as in engines and rockets [18,[43][44][45], a distortion ratio of 20% was also used in I 0,1 to measure the CO 2 concentrations under similar conditions. Under conditions of such large offsets, the m-FID method yields errors of only 3% and 2% in the average values for the up-and down-scans while DAS gives errors of 6% and 3%.…”

Kinetics of methyl methacrylate (MMA) combustion assessed by time-resolved speciation behind shock waves

“…The first form is typically employed when a comprehensive line-by-line spectral database of an absorbing species is confidently known and the spectral transitions are easily separable in the absorbance measurement. This form is used in the present study to evaluate the concentration of CO and CO 2 , and is discussed at length in prior work [14,15]. The second cross-section formulation of the Beer-Lambert law is appropriate for broadly-absorbing species for which the temperature-dependent line-by-line spectroscopy is less well-known and/or the absorbance spectra are convoluted enough to preclude identification of individual spectral transitions from the absorbance measurement.…”

“…Likewise, the ICL targeting CO 2 provides a scan depth of 1.1 cm −1 over the R(0,62) line of CO 2 's (01 0 0 → 01 0 1) 3 fundamental band near 2386 cm −1 , while the QCL provides a scan depth of 1.45 cm −1 over the P(0,31) and P(2,20) lines of CO's fundamental band near 2008.5 cm −1 . These wavelength regions for CO 2 and CO have been targeted in previous investigations by the authors for temperature and concentration measurements in hybrid rocket flows [14,15] and are not detailed further here. All lasers are scanned at 40 kHz using a triangle wave; both the up-and down-scan are leveraged to increase the effective measurement rate to 80 kHz; representative scans for both the incident ( 0 ) and transmitted ( ) intensity of the 3.6 µm ICL are shown in the right of Fig.…”

“…Owing to its relatively simple depolymerization and thermal decomposition behavior, poly(methyl methacrylate) (PMMA) has been studied for several decades by both the fire science and propulsion communities [8][9][10][11][12][13][14][15][16]. Since the pyrolysis kinetics of PMMA are not complicated by charring or cross-linking behavior, its constituent monomer methyl methacrylate (MMA, C 5 H 8 O 2 ) accounts for nearly 95% of its pyrolysis products, historically providing a tractable and accessible modeling framework for PMMA combustion.…”

Localized characteristic velocity (c*) for rocket combustion analysis based on gas temperature and composition via laser absorption spectroscopy

“…LAS is an optical diagnostic technique known for its quantitative, species-specific measurement capability, which, when combined with tomographic reconstruction methods [9][10][11], can be used to characterize reacting flow-fields in harsh combustion environments [12][13][14][15]. Simultaneous multispecies measurements, in particular, provide key insights into the physiochemical mechanisms governing combustion performance and further elucidate complex combustion physics [16][17][18].…”