New laser-based instrument designed to advance hydrogen research

Optics Express (2022). doi: 10.1364/OE.465817″ width=”800″ height=”469″/>

(a) Power and Feynman plots for the resonant (left) and non-resonant (right) paths. (b) Polarization angles of the resonant (blue line) and non-resonant (red line) CRS signals, and, represented by the elevation angle on the unit sphere as a function of the relative polarization angle (azimuthal angle) of the pump/Stokes and probe fields, α. (C) Schematic of a polarization-sensitive coherent imaging spectrometer. OW, optical window; SL, spherical lenses; m, BPF mirror, band-pass filter; PBS, polarizing beam splitter; FR, Fresnel rhomb; BS, beam stop. Inset: probe size. The probe crosses the high-speed pump/Stokes beam ∼2mm past the end of the filament. Increasing the input power causes the filament to elongate towards the focusing optics (arrow direction) (d) Measurements points across the air/H2 flame interface, and the red dashed line marks the location of the burner edge at y = 9.5 mm. attributed to him: Optix Express (2022). doi: 10.1364/OE.465817

Researchers have developed an analytical instrument that uses a high-speed laser for precise measurements of temperature and hydrogen concentration. Their new approach could advance the study of greener hydrogen-based fuels for use in spacecraft and aircraft.

“This tool will provide powerful capabilities for probing dynamic processes such as diffusion and mixing The transfer of energy And the chimical interaction“Understanding these processes is key to developing more environmentally friendly propulsion engines,” said research team leader Alexis Bohlin from Luleå University of Technology in Sweden.

in Optix ExpressBohlin and colleagues from Delft University of Technology and Vrije Universiteit Amsterdam, both in the Netherlands, describe a new, coherent Raman spectroscopic instrument for the study. hydrogen. This is made possible because of a setup that converts broadband light from a laser with short pulses (femtoseconds) into ultrashort pulses, which have a wide range of wavelengths.

The researchers showed that this super-vacuum generation could be performed behind the same type of thick optical windows found in hyperbaric chambers used to study a hydrogen-based structure. engine. This is important because other methods of generating ultra-wideband excitation do not work when these types of optical windows are present.

Hydrogen-rich fuel, when made from renewable resourcescan have a significant impact on emissions reduction and make a significant contribution to mitigation anthropogenic climate change“Our new method can be used to study these fuels under conditions very similar to those found in rocket and aviation engines,” Bohlin said.

get light

There is great interest in developing space engines that run on hydrogen-rich renewable fuels. In addition to their sustainability appeal, these fuels have the highest achievable specific thrust—a measure of how efficiently a chemical reaction in an engine is creating thrust. However, it has been very difficult to make hydrogen-based chemical propulsion systems reliable. This is because the increased reactivity of hydrogen-rich fuels significantly changes the combustion properties of the fuel mixture, increasing the flame temperature and reducing ignition delay times. Also, combustion in rocket engines in general is very difficult to control due to the extremely high pressures and high temperatures that are encountered when space travel.

“The progress of technology for sustainable launch and propulsion systems in space depends on a coherent interaction between experiments and modelling,” Bohlin said. “However, many challenges remain in terms of producing reliable quantitative data to validate models.”

One obstacle is that experiments are usually conducted in an enclosed space with limited transmission of light signals in and out through optical windows. This window can cause the supercontinuity pulses needed for coherent Raman spectroscopy to stretch as they pass through the glass. To get around this problem, the researchers developed a method for transmitting a femtosecond pulsed laser through a thick optical window and then used a process called laser-induced filament to convert it into ultra-continuous pulses that stay coherent on the other side.

Hydrogen flame study

To demonstrate the new tool, the researchers created a femtosecond laser beam with optimal properties for supercurrent generation. Then they used it to perform coherent Raman spectroscopy by means of exciting hydrogen molecules and to measure their spin shifts. They were able to demonstrate robust measurements of hydrogen gas over a wide range of temperatures and concentrations, and also analyzed hydrogen/air diffusion flames similar to what can be seen when it is hydrogen-rich. fuel Burnt.

The researchers are now using their instruments to perform a detailed analysis of turbulent hydrogen flames in the hope of making new discoveries about the combustion process. With the aim of adopting a research and testing method for rocket engines, scientists are exploring the limits of this technology and would like to test it using hydrogen flames in a closed, slightly pressurized shell.


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more information:
Francesco Mazza et al., Coherent Raman spectroscopy on hydrogen with in situ generation, in situ use, and in situ signaling for ultra-wideband excitation, Optix Express (2022). doi: 10.1364/OE.465817

the quote: New laser-based instrument designed to boost hydrogen research (2022, September 13) Retrieved September 15, 2022 from

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