arXiv subjects

Jesse W. Streicher

Publications and source records attributed to Jesse W. Streicher.

2 recordsLinked to original sources

arXiv2026

Combined Absorption and Emission Study of Air Species in NASA EAST

A suite of tunable diode laser absorption spectroscopy (TDLAS) diagnostics targeting rovibrational states of nitric oxide (NO) in the mid-infrared (MIR) and electronic states of atomic oxygen (O) and nitrogen (N) in the near-IR (NIR) was combined with optical emission spectroscopy (OES) for overlapping wavelengths at the NASA Electric Arc Shock Tube (EAST) facility for three selected high-temperature air experiments. Absorption features were probed at rates up to 1 MHz to provide quantitative, time-resolved measurements of temperature and species number density profiles behind incident shocks, enabling comparisons to spatially-resolved emission measurements, with the two typically agreeing within their respective uncertainties. Inferred time-histories are further compared to incident shock simulations from two one-dimensional models - one leveraging the Park two-temperature rates and the other more recent rate values - as well as the Data Parallel Line Relaxation (DPLR) code. For the two low-velocity cases (3.81 and 3.98 km/s) in which NO is probed, inferred temperatures are typically well-captured by all three models, although the NO number densities show stronger variation, agreeing better for the model with updated NO formation and dissociation rates. Finally, one high-velocity case (7.03 km/s) demonstrates the simultaneous resolution of three O-atom and six N-atom electronic states, with all states showing a steady increase in number density over time - possibly due to shock trajectory effects. Together, this combined absorption and emission study demonstrates resolution of many states of nonequilibrium air species, while directly comparing ground- and excited-state populations via the combined diagnostic strategy.

physics.chem-ph↗

arXiv2026

Carbon black and hydrogen production from methane pyrolysis: measured and modeled insights from integrated gas and particle diagnostics in shock tubes

Methane (CH4) pyrolysis is a promising route to co-produce hydrogen (H2) and carbon black (CB) while avoiding emissions associated with steam-methane reforming and furnace black processes. Model development of pyrolytic CB synthesis requires experimental observations of concurrent gas chemistry, particulate formation, and morphology. This work presents a combined experimental and modeling study of CH4 pyrolysis behind reflected shock waves in 5% CH4/Argon mixtures at post-reflected shock temperatures (T5) of 1850-2450 K and P5 around 4.5 atm. Laser absorption diagnostics quantified CH4, C2H4, and C2H2 mole fractions, while multiwavelength extinction (633 and 1064 nm) resolved time-dependent particle formation and the temperature-dependent evolution of optical maturity. Simulations reproduce small-molecule speciation well, but large variations in predicted polycyclic aromatic hydrocarbons (PAHs) persist among models. Coupled gas-particle simulations capture accurate volume fraction (fv) trends and the influence of gas dynamics but underpredict induction times at high T5. Samples collected at the shock tube endwall were analyzed by transmission electron microscopy (TEM) to quantify primary particle size distributions and nanostructure arrangement. Image segmentation and manual measurements showed reduced primary particle size growth (dp) with increasing T5, while graphitic nanostructure generally increased. This study provides an integrated benchmark for improving models of CB and H2 production from CH4 pyrolysis by constraining gas-phase kinetics, PAH-driven inception, particle dynamics, and particle maturity. The results highlight that accurate partitioning of mass between particle number and particle size is an important constraint for further model development.

physics.chem-ph↗