Papers by Nicolas Pinkowski
SAE International Journal of Engines
Proceedings of the 32nd International Symposium on Shock Waves (ISSW32 2019), 2019
A collection of high-temperature absorption cross-sections for hydrocarbon in the mid-infrared.
Proceedings of the 32nd International Symposium on Shock Waves (ISSW32 2019), 2019
International Journal of Chemical Kinetics, 2020
The pyrolysis of propane plays an important role in determining the combustion properties of natu... more The pyrolysis of propane plays an important role in determining the combustion properties of natural gas mixtures and offers insight into the cracking patterns of larger fuels. This work investigates propane pyrolysis behind reflected shock waves with a multi-wavelength laserabsorption speciation technique. Nine laser wavelengths, sensitive to key pyrolysis species, were used to measure absorbance time-histories during the decomposition of 2% propane in argon between 1022-1467 K, 3.7-4.3 atm. Absorbance models were developed at each diagnostic wavelength to interrogate common initial conditions, and time-histories of all major species are reported at 1250 K, 1290 K, 1330 K, 1370 K, and 1410 K. Nearly complete carbon recovery observed at lower temperatures enabled the inference of hydrogen formation from atomic conservation, while decaying carbon recovery at high temperatures suggests the formation of allene and 1-butene. The results show systematically faster pyrolysis than predicted by kinetic modeling and motivate further study into the kinetics of propane pyrolysis.
Measurement Science and Technology, 2021
Quantum-cascade-laser dual-comb spectroscopy (QCL-DCS) is a promising technology with ultra-fast ... more Quantum-cascade-laser dual-comb spectroscopy (QCL-DCS) is a promising technology with ultra-fast time resolution capabilities for chemical kinetics, atmospheric gas sensing, and combustion applications. A pair of quantum-cascade frequency combs were used to measure absorbance from methane’s ν4 band between 1270 and 1315 cm−1 at high-temperature and -pressure conditions that were generated using a high-pressure shock tube. Results here mark a major improvement over previous QCL-DCS measurements in shock tubes. Improvements came from a unique spectral-filtering strategy to correct for a bimodal power-spectral density of QCL frequency combs and careful optimization of the laser setup and experimental conditions. Our modified QCL-DCS was ultimately used to measure temperature within 2% and methane mole fraction within 5% by fitting HITEMP spectral simulations to spectra recorded at 4 μs temporal resolution. We measure temperature and species time-histories during methane pyrolysis at conditions between 1212–1980 K, and 12–17 atm, all at 4 μs resolution. Good agreement is observed with kinetic models, illustrating the potential of future applications of DCS in kinetics and combustion research.
Measurement Science and Technology, 2020
This work presents a methodology for using spectroscopic models to fit absorption-spectrum measur... more This work presents a methodology for using spectroscopic models to fit absorption-spectrum measurements made by a quantum-cascade-laser-based dual-comb spectrometer (QCL-DCS) for high-temperature kinetics research. A pair of quantum-cascade frequency combs was employed to detect methane’s ν 4 absorption features between 1270 and 1320 cm−1 in high-temperature shock-tube environments and extract methane mole fraction and gas temperature from the results. The methodology was first validated by comparing DCS measurements against modeled methane spectra at room temperature in a static cell, followed by assessing the fitting procedure in shock-heated mixtures of 2% methane in Ar at 1000 K. In both validation experiments, the tradeoffs between time resolution and measurement precision were explored. Measurements were achieved at a 4 µs measurement rate with 5% uncertainty for temperature and 4% uncertainty for mole fraction at 1000 K. Higher accuracy was achieved with longer measurement av...
Fuel, 2020
Abstract Ethane pyrolysis chemistry plays a critical role in the combustion behavior of natural g... more Abstract Ethane pyrolysis chemistry plays a critical role in the combustion behavior of natural gas and gives insight into the decomposition patterns of larger alkanes. In this work, ethane pyrolysis was studied behind reflected shock waves with a convex optimization-based laser absorption speciation technique. Species time-histories of ethane, ethylene, methane, and acetylene were quantified in the decomposition of 1% and 2% ethane in argon at conditions between 1178 and 1527 K and 3.1–4.2 atm. Six laser wavelengths, simultaneously probing sensitive regions of each species’ spectra, enabled the sensitive detection of all major pyrolysis products and confirmed the negligible formation of other species. The time-history data presented in this work paint a coherent picture of ethane decomposition that motivates specific refinements to state-of-the-art detailed kinetic models.
Fuel, 2020
The speciation of jet-fuel pyrolysis plays an important role in the development of predictive mod... more The speciation of jet-fuel pyrolysis plays an important role in the development of predictive models for jet-fuel combustion. In this work, a multi-wavelength speciation technique was applied to a large dataset of shock-tube laser-absorption measurements of jet-fuel pyrolysis. A novel absorbance model was developed to interpret the measurements at common conditions, and pyrolysis product time-histories and early-time yields are reported for three jet fuels at five high-temperature conditions. Specifically, methane, ethylene, and lumped vinyl-group time-histories, in addition to aromatics (benzene and toluene) yields, were quantified using eight wavelengths over conditions 1040-1480 K, 1-3 atm, for jet fuels JP8, Jet-A, and JP5. Results are presented at 1150 K, 1200 K, 1250 K, 1300 K, and 1350 K. Additional relationships between vinyl-group-containing species, namely propene, 1-butene, and 1,3-butadiene, are explored. The mole fraction time-histories exhibit good agreement with the literature and extend the speciation of these jet fuels to the limits of current spectroscopic techniques.
Measurement Science and Technology, 2020
In the current study, a quantum-cascade-laser-based dual-comb spectrometer (DCS) was used to pain... more In the current study, a quantum-cascade-laser-based dual-comb spectrometer (DCS) was used to paint a detailed picture of a 1.0 ms high-temperature reaction between propyne and oxygen. The DCS interfaced with a shock tube to provide pre-ignition conditions of 1225 K, 2.8 atm, and 2% p-C3H4/18% O2/Ar. The spectrometer consisted of two free-running, non-stabilized frequency combs each emitting at 179 wavelengths between 1174 and 1233 cm-1. A free spectral range, , of 9.86 GHz and a difference in comb spacing, Δ , of 5 MHz, enabled a theoretical time resolution of 0.2 µs but the data was time-integrated to 4 µs to improve SNR. The accuracy of the spectrometer was monitored using a suite of independent laser diagnostics and good agreement observed. Key challenges remain in the fitting of available high-temperature spectroscopic models to the observed spectra of a post-ignition environment.
Combustion and Flame, 2019
The development of renewable, alternative jet fuels presents an exigent challenge to the aviation... more The development of renewable, alternative jet fuels presents an exigent challenge to the aviation community. In this work, a streamlined methodology for building computationally efficient kinetic models of real fuels from shock tube experiments is developed and applied to a low cetane-number, broad-boiling alternative jet fuel (termed C-4). A multi-wavelength laser absorption spectroscopy technique was used to determine species time-histories during the high-temperature pyrolysis of C-4, and a batch gradient descent optimization routine built a hybrid-chemistry (HyChem) kinetic model from the measured data. The model was evaluated using combustor-relevant, high-pressure ignition delay time measurements with satisfactory agreement. The present model enables predictive simulations of C-4 in practical environments, while the underlying methodology described here can be readily extended to build kinetic models for a broad range of real fuels of interest.
Journal of Quantitative Spectroscopy and Radiative Transfer, 2018
The development of kinetics mechanisms to model jet fuel combustion requires detailed information... more The development of kinetics mechanisms to model jet fuel combustion requires detailed information about the high-temperature pyrolysis products of these fuels. This study presents a method to measure the mole fractions of the important decompositions products, i.e. CH4, C2H4, C3H6, i-C4H8, 1-C4H8, C6H6, C7H8, and fuel that form during thermal decomposition (pyrolysis) of conventional and alternative jet fuels. This method combines the use of shock tubes, laser absorption spectroscopy, and a mathematical method commonly employed in machine learning (convex optimization) to determine species mole fractions during pyrolysis experiments. This approach is possible because of the development of a large spectroscopic database of absorption cross sections measured for 8 species at 8 wavelengths that has recently been compiled from over 1200 shock tube measurements. Using this spectral database in conjunction with laser absorption measurements in a shock tube at 8 wavelengths, species time-h...
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Papers by Nicolas Pinkowski