Ammonia Pyrolysis behind Reflected Shock Waves: Multispecies Measurements and Modeling

Area of Science:

• Chemical Kinetics
• Combustion Science
• Spectroscopy

Background:

• Ammonia (NH3) pyrolysis significantly impacts ignition and NOx production, but current chemical kinetic models are inadequate.
• Lack of simultaneous, multispecies data hinders refinement of NH3 pyrolysis models.

Purpose of the Study:

• To obtain simultaneous measurements of NH, NH2, and NH3 during NH3 pyrolysis.
• To refine existing chemical kinetic models for NH3 pyrolysis.
• To provide data for improving predictions of NH3 oxidation.

Main Methods:

• Pyrolysis of dilute NH3 in argon behind reflected shock waves (2100-3500 K).
• Laser absorption diagnostics to measure NH, NH2, and NH3 concentrations.
• Enabled refined measurements of the NH2 absorption feature's oscillator strength.

Main Results:

• First simultaneous measurements of NH, NH2, and NH3 during NH3 pyrolysis achieved.
• Developed a refined NH3 pyrolysis model, improving predictions of species time-histories.
• Significantly improved predictions for late-time NH2 consumption and early-time NH formation.

Conclusions:

• Simultaneous multispecies data are crucial for refining NH3 pyrolysis models.
• The refined model shows improved accuracy in predicting key reaction pathways.
• Further research with hydrazine and hydrazoic acid precursors is needed for comprehensive NH3-relevant species data.