Formaldehyde preparation methods for pressure and temperature dependent laser-induced fluorescence measurements

Area of Science:

• Combustion Science
• Chemical Physics

Background:

• Formaldehyde is crucial for studying hydrocarbon fuel ignition.
• Laser-induced fluorescence (LIF) is vital for measuring formaldehyde concentrations.
• High temperatures and pressures cause formaldehyde's rapid decomposition, complicating LIF measurements.

Purpose of the Study:

• To develop and evaluate calibration cell setups for improved formaldehyde LIF measurements.
• To investigate formaldehyde behavior under various conditions relevant to combustion.
• To overcome challenges associated with formaldehyde's thermal instability during measurements.

Main Methods:

• Evaporation of paraformaldehyde to create formaldehyde.
• Three distinct calibration cell setups were designed and tested: a basic resist heater setup, a constant flow system with preheated air, and a novel laser-based rapid heating system using SF6 and CO2.
• Laser-induced fluorescence (LIF) and Raman scattering were employed for spectral analysis and temperature measurement.

Main Results:

• The constant flow system reduced gas heating time.
• The laser-based rapid heating system minimized gas heating time and thermal decomposition.
• New pressure-dependent LIF excitation spectra of formaldehyde were obtained in the 343 nm region.
• The laser heating system's applicability was demonstrated with various gas mixtures.

Conclusions:

• The developed calibration cell setups enhance the accuracy and reliability of formaldehyde LIF measurements.
• The novel laser-based rapid heating system offers a significant advancement for studying transient species like formaldehyde in combustion.
• These methods provide better characterization of formaldehyde's role in early ignition phases.