High-speed 2D Raman imaging at elevated pressures.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Fluid Dynamics

Background:

• Accurate characterization of non-reacting flows is essential for understanding combustion processes.
• Previous methods often lack the speed and spatial resolution required for dynamic flow analysis.
• Optical breakdown limits laser-based diagnostic techniques in high-energy applications.

Purpose of the Study:

• To demonstrate two-dimensional (2D) Raman scattering for high-speed, single-shot imaging of non-reacting flows.
• To investigate the influence of laser pulse parameters on measurement quality.
• To apply the technique for analyzing fuel-air mixing at elevated pressures.

Main Methods:

• Utilized a burst-mode laser operating at 10 kHz with long-duration pulses (70 ns, 750 mJ at 532 nm).
• Varied laser pulse width (10-1000 ns) to prevent optical breakdown.
• Performed 2D Raman scattering measurements on methane (CH4) and hydrogen (H2) jets in nitrogen (N2) at elevated pressures.

Main Results:

• Successfully demonstrated high-speed, single-shot 2D imaging of CH4 and H2 jets.
• Analyzed the effects of pulse shape, energy, and harmonic conversion on 2D measurement accuracy.
• Determined the scalar dissipation rate of CH4 in N2 at 20 bar.

Conclusions:

• The developed 2D Raman scattering technique provides high-speed, multi-dimensional imaging capabilities for complex flows.
• This method is effective for analyzing fuel-air mixing and scalar properties in non-reacting flows at high pressures.
• The findings support advanced diagnostics for combustion and other high-pressure fluid dynamic applications.