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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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31 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

10-kHz PLIF Thermometry for a Turbulent Jet Flame using Single Burst-mode OPO

Two-color Planar laser-induced fluorescence (TC-PLIF) thermometry techniques that employ two laser systems and two cameras face challenges when implemented in practical combustion facilities because of experimental complexity and multiple laser and camera requirements, particularly for high-speed TC-PLIF. To circumvent those problems, we developed a fast, dual-wavelength switching, burst-mode OPO technology to significantly reduce the experimental complexity of high-speed TC-PLIF thermometry and simplify its implementation in harsh combustion and flow test facilities. A fast, dual-wavelength switched seed laser enabled a high-energy, high-repetition-rate burst-mode laser to generate two 10-kHz pulse trains at wavelengths of ~354.8 nm. The injection-seeded OPO efficiently converts the burst-mode laser output to285.62 nm and 285.67 nm to excite the Q2(12) and P1(8) OH transitions. PLIF images were collected from each of the two excitation transitions with a single camera and an UV intensifier, and intensity ratios from the images were used to determine local temperatures. Ten kHz hydroxyl radical (OH) TC-PLIF for premixedCH4/Air/H2 jet flame was demonstrated.

thermometry↗
NASA NTRSDate not supplied

10-kHz PLIF Thermometry for Turbulent Jet Flame using Single Burst-mode OPO

Two-color Planar Laser-Induced Fluorescence (TC-PLIF) thermometry techniques that employ two laser systems and two cameras face challenges when implemented in practical combustion facilities because of experimental complexity and multiple laser and camera requirements, particularly for high-speed TC-PLIF. To circumvent those problems, we developed a fast, dual-wavelength switching, burst-mode OPO technology to significantly reduce the experimental complexity of high-speed TC-PLIF thermometry and simplify its implementation in harsh combustion and flow test facilities. A fast, dual-wavelength switched seed laser enabled a high-energy, high-repetition-rate burst-mode laser to generate two 10-kHz pulse trains at wavelengths of ~354.8 nm. The injection-seeded OPO efficiently converts the burst-mode laser output to 285.62 nm and 285.67 nm to excite the Q2(12) andP1(8) OH transitions. PLIF images were collected from each of the two excitation transitions with a single camera and an UV intensifier, and intensity ratios from the images were used to determine local temperatures. Ten kHz hydroxyl radical (OH) TC-PLIF for premixedCH4/Air/H2 jet flame was demonstrated.

thermometry↗
DOE OSTI2022

Noncolinear optical parametric oscillator for broadband nanosecond pulse-burst CARS diagnostics in gases

We report demonstration of broadband nanosecond coherent anti-Stokes Raman scattering (CARS) using a burst-mode-pumped noncolinear optical parametric oscillator (NOPO) has been achieved at a pulse repetition rate of 40 kHz. The NOPO is pumped with the 355-nm output of a burst-mode Nd:YAG laser at 50 mJ/pulse for 45 pulses and produces an output centered near 607 nm, with a bandwidth of 370 cm –1 at energies of 5 mJ/pulse. A planar BOXCARS phase matching scheme uses the broadband NOPO output as the Stokes beam and the narrowband 532-nm burst-mode output for the two CARS pump beams for single-laser-shot nitrogen thermometry in near adiabatic H 2 /air flames at temperatures up to 2200 K.

47 OTHER INSTRUMENTATION↗
NASA NTRSDate not supplied

Investigation of Liquid Fuel Injection Processes in a Rotating Detonation Combustor using Megahertz Planar Laser-Induced Fluorescence Imaging

Direct imaging of liquid fuel injection is performed within an optically accessible rotating detonation combustor (RDC) using planar laser-induced fluorescence (PLIF) to spatio-temporally resolve the highly dynamic spray characteristics at rates up to 1 MHz. The RDC is operated on air and hydrogen to sustain a stable, cyclically propagating detonation wave with cycle periods of up to ∼250 μs. One of the hydrogen fuel injection sites is replaced with a liquid jet to introduce a diesel spray as a fuel surrogate to enable tracer-free fluorescence excitation using the 355 nm third-harmonic output of a burst-mode Nd:YAG laser. The time-resolved PLIF measurements reveal the evolution of the highly unsteady spray, including the dwell period after the arrival of the detonation wave, the jet recovery, breakup and entrainment into the supersonic crossflow of air, propagation into the detonation chamber, and interaction with the detonation wave. Following passage of the detonation wave, the spray characteristics reveal significant changes in the momentum flux ratio between the liquid and air streams, altering the jet trajectory and temporarily halting fuel delivery to the detonation channel. This temporary cessation of fuel spray injection into the combustor is quantified, along with the fill rate as a function of time. As the injection system recovers, the fuel spray eventually returns to a quasi-steady position prior to the arrival of the detonation wave, allowing qualitative comparisons with theoretical jet trajectories for a range of air mass-flux conditions. These data, enabled by ultra-high-speed PLIF imaging, represent some of the first detailed measurements for characterizing and quantifying the interactions of liquid jets and detonations in an operating RDC.

Propulsion↗
NASA NTRSDate not supplied

Investigation of Liquid Fuel Refill Dynamics in a Rotating Detonation Combustor using Megahertz Planar Laser-Induced Fluorescence

Direct imaging of liquid fuel injection is performed within an optically accessible rotating detonation combustor (RDC) using planar laser-induced fluorescence (PLIF) to spatio-temporally resolve the highly dynamic spray characteristics at rates up to 1 MHz. The RDC is operated on air and hydrogen to sustain a stable, cyclically propagating detonation wave with cycle periods of up to ∼250 μs. One of the hydrogen fuel injection sites is replaced with a liquid jet to introduce a diesel spray as a fuel surrogate to enable tracer-free fluorescence excitation using the 355 nm third-harmonic output of a burst-mode Nd:YAG laser. The time-resolved PLIF measurements reveal the evolution of the highly unsteady spray, including the dwell period after the arrival of the detonation wave, the jet recovery, breakup and entrainment into the supersonic crossflow of air, propagation into the detonation chamber, and interaction with the detonation wave. Following passage of the detonation wave, the spray characteristics reveal significant changes in the momentum flux ratio between the liquid and air streams, altering the jet trajectory and temporarily halting fuel delivery to the detonation channel. This temporary cessation of fuel spray injection into the combustor is quantified, along with the fill rate as a function of time. As the injection system recovers, the fuel spray eventually returns to a quasi-steady position prior to the arrival of the detonation wave, allowing qualitative comparisons with theoretical jet trajectories for a range of air mass-flux conditions. These data, enabled by ultra-high-speed PLIF imaging, represent some of the first detailed measurements for characterizing and quantifying the interactions of liquid jets and detonations in an operating RDC.

Propulsion↗
NASA NTRSDate not supplied

Time Resolved Visualization of A Liquid Jet in an RDE Using MHz Rate Diesel PLIF

The characterization of the dynamic response of liquid jets to transient detonation wave passage is critical for optimization and modeling of liquid fueled rotating detonation combustors. In this work, a rotating detonation combustor (RDC) is operated on hydrogen and air to sustain stable detonation waves that acts as a detonation driver and interact in a one-way coupled manner with a single liquid fuel jet that propagates into the combustion chamber with cycle periods of ~ 250 μs. Diesel is utilized as a realistic fuel surrogate with higher aromatic compounds to enable fluorescence excitation, using the 355 nm third harmonic output of a burst-mode Nd:YAG laser, imaged at rates up to 1 MHz. By optimizing the technique to accommodate orders of magnitude variations in the fuel density throughout the injection process, the PLIF data enable quantitative measurements including the refill time, the relative recovery between liquid and gaseous jets and jet trajectory across various momentum flux ratio. As the passage of the detonation wave imparts significant changes in the momentum flux ratio, the qualitative liquid break-up process and spatial distribution varies significantly in time. As the injection system recovers ~ 70% of the cycle period and return to a quasi-steady position and allow comparisons with theoretical jet trajectories. These data, enabled by ultra-high-speed PLIF imaging, represent some of the first detailed measurements for quantifying the dynamic response and recovery of liquid jets exposed to periodic detonations in an operating RDC.

Propulsion↗
NASA NTRSDate not supplied

Time Resolved Visualization of Liquid Jet Interaction With H2-Air Rotating Detonations Using MHz Rate Diesel PLIF

The characterization of the dynamic response of liquid jets to transient detonation wave passage is critical for optimization and modeling of liquid fueled rotating detonation combustors. In this work, a rotating detonation combustor (RDC) is operated on hydrogen and air to sustain stable detonation waves that acts as a detonation driver and interact in a one-way coupled manner with a single liquid fuel jet that propagates into the combustion chamber with cycle periods of ~ 250 μs. Diesel is utilized as a realistic fuel surrogate with higher aromatic compounds to enable fluorescence excitation, using the 355 nm thirdharmonic output of a burst-mode Nd:YAG laser, imaged at rates up to 1 MHz. By optimizing the technique to accommodate orders of magnitude variations in the fuel density throughout the injection process, the PLIF data enable quantitative measurements including the refill time, the relative recovery between liquid and gaseous jets and jet trajectory across various momentum flux ratio. As the passage of the detonation wave imparts significant changes in the momentum flux ratio, the qualitative liquid break-up process and spatial distribution varies significantly in time. As the injection system recovers ~ 70% of the cycle period and return to a quasi-steady position and allow comparisons with theoretical jet trajectories. These data, enabled by ultra-high-speed PLIF imaging, represent some of the first detailed measurements for quantifying the dynamic response and recovery of liquid jets exposed to periodic detonations in an operating RDC.

Propulsion↗
DOE OSTI2024

High-efficiency narrow-bandwidth KTP optical parametric oscillator for kHz–MHz planar laser-induced fluorescence

The electronic excitation of key combustion species or flow tagging of chemical species requires a narrowband tunable UV source. In this work, a potassium titanyl phosphate (KTP) burst-mode optical parametric oscillator (OPO) pumped by a 532 nm laser is developed to generate a spectrally narrow signal and an idler output with 1.48 ± 0.19 cm −1 bandwidth without the need for injection seeding. The idler (1410–1550 nm range) is further mixed with 355 or 266 nm to generate 284 or 226 nm for OH or NO planar laser-induced fluorescence (PLIF), respectively, with up to 1.9% conversion efficiency from 1064 nm to the UV. MHz-rate burst profiles are reported, and OH and NO PLIF are demonstrated in a rotating detonation combustor at rates up to 200 kHz.

Webb, Austin M. (ORCID:0000000155897474)↗
DOE OSTI2024

Controlled molecule injector for cold, dense, and pure molecular beams at the European x-ray free-electron laser

A permanently available molecular-beam injection setup for controlled molecules (COMO) was installed and commissioned at the small quantum systems (SQS) instrument at the European x-ray free-electron laser (EuXFEL). A b-type electrostatic deflector allows for pure state-, size-, and isomer-selected samples of polar molecules and clusters. The source provides a rotationally cold (T ≈ 1 K) and dense (ρ ≈ 10 8 cm −3 ) molecular beam with pulse durations up to 100 µs generated by a new version of the Even-Lavie valve. Here, a performance overview of the COMO setup is presented along with characterization experiments performed both with an optical laser at the Center for Free-Electron-Laser Science and with x rays at EuXFEL under burst-mode operation. COMO was designed to be attached to different instruments at the EuXFEL, in particular, the SQS and single particles, clusters, and biomolecules (SPB) instruments. This advanced controlled-molecules injection setup enables x-ray free-electron laser studies using highly defined samples with soft and hard x-ray FEL radiation for applications ranging from atomic, molecular, and cluster physics to elementary processes in chemistry and biology.

He, Lanhai↗
DOE OSTI2025

Flow visualization in high-energy-density laboratory plasmas

Flow visualization is often essential for evaluating high-energy-density (HED) laboratory plasmas, examining their dynamics, and assessing design strategies. However, imaging at fine phenomenological flow scales is a major challenge. Here, a zone-plate–based radiography system tailored for applications in HED physics is demonstrated. The burst-mode radiography system combines a dual-flash laser-generated x-ray source, a high-magnification zone plate optic, and a multiple frame hybrid complementary metal-oxide-semiconductor (hCMOS) sensor for image detection. Operating at a magnification of 42 x⁠, a pair of radiographs is measured in rapid succession, each time gated by a 4.75 keV flash of x rays lasting 100 ps. The system achieves a spatial resolution below 3 μm. The potential of this approach for applications in HED physics is exemplified by observing small-scale spike morphologies at a pusher-foam interface impacted by a strong, laser-driven blast wave.

Flow instabilities↗
DOE OSTI2022

Burst-mode chirped pulse amplification method

A method for increasing the MeV hot electron yield and secondary radiation produced by short-pulse laser-target interactions with an appropriately high or low atomic number (Z) target. Secondary radiation, such as MeV x-rays, gamma-rays, protons, ions, neutrons, positrons and electromagnetic radiation in the microwave to sub-mm region, can be used, e.g., for the flash radiography of dense objects.

Bude, Jeffrey D.↗
DOE OSTI2021

Burst-mode dual-comb spectroscopy

We introduce a new modality of dual-comb spectroscopy that enables a simplified and powerful new approach for time-resolved measurements with increased acquisition rates. This "burst mode" form of dual-comb spectroscopy (BM-DCS) relies on the multiplexing of each probe pulse into a short train of pulses. With this approach we demonstrate a time-resolved series of absorption-based spectroscopic measurements of a laser-induced plasma using only a single laser ablation shot and identify 22 Nd lines not previously reported in the literature. The transmission spectra spanned 3.1 THz and were acquired at an effective acquisition rate of 25 kHz with 40 ms time-resolution. This simple modification to 100 MHz level dual-comb systems provides a flexible approach for studying transient and low duty-cycle events such as laser-induced plasmas, combustion, and explosive reactions.

(280.5395) Plasma Diagnostics, broadband laser spe↗