Air Humidity Influence on Combustion of R-1234yf (CF₃CFCH₂), R-1234ze(E) (trans-CF₃CHCHF) and R-134a (CH₂FCF₃)...

Area of Science:

• Combustion Science and Engineering
• Chemical Kinetics and Reaction Mechanisms

Background:

• Hydrofluorocarbons (HFCs) are used in various applications, and understanding their combustion behavior, especially in the presence of air humidity, is crucial.
• HFC flames exhibit a two-stage reaction mechanism, with a transition from a fast initial stage to a slow second stage.
• The role of water vapor as a potential additive in HFC combustion requires detailed investigation.

Purpose of the Study:

• To investigate the influence of air humidity (water vapor) on flame propagation in hydrofluorocarbon-air mixtures.
• To analyze the reaction pathways and kinetics affected by water vapor addition.
• To compare numerical simulation results with experimental data for validation.

Main Methods:

• Numerical simulations of flame propagation in hydrofluorocarbon-air mixtures.
• Analysis of reaction kinetics and radical production mechanisms.
• Comparison of calculated burning velocities with literature experimental data for R-1234yf and R-1234ze(E).

Main Results:

• Water vapor addition increases radical production (H, O, OH) and accelerates the overall reaction rate in HFC flames.
• The reaction H₂O + F = HF + OH is identified as a key pathway for radical generation and combustion enhancement.
• Simulated burning velocities, particularly the shift of maximum burning velocity to leaner mixtures with water vapor, show good agreement with experimental data.

Conclusions:

• Water vapor significantly enhances the burning velocity of HFC flames, primarily by influencing the first stage of the two-stage combustion process.
• The findings highlight the importance of considering humidity effects in HFC combustion modeling and safety assessments.
• The study validates the role of specific reaction pathways in mediating the combustion enhancement by water vapor.