Numerical study of gas-phase interactions of phosphorus compounds with co-flow diffusion flames

Area of Science:

• Combustion Science
• Chemical Kinetics
• Flame Inhibition

Background:

• Methane-air diffusion flames are crucial in combustion research.
• Phosphorus-containing compounds (PCCs) are explored as flame retardants.
• Understanding their inhibition mechanisms is vital for safety.

Purpose of the Study:

• To computationally investigate the effects of PCCs on methane-air coflow diffusion flames.
• To analyze flame structure and inhibition processes with different PCCs.
• To compare the effectiveness of PCCs added to fuel versus oxidizer streams.

Main Methods:

• Time-dependent axisymmetric computation with full gas-phase chemistry and transport.
• Detailed chemical-kinetics model incorporating methane combustion and phosphorus inhibition.
• Incorporation of a radiation model for key combustion products.
• Calculation of Minimum Extinguishing Concentrations (MECs) for CO2 with PCCs.

Main Results:

• PCCs lower radical concentrations and heat-release rate at the flame base, promoting blow-off.
• Inhibitor effectiveness is an order of magnitude higher when added to the oxidizer stream.
• Dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP) create a two-zone flame structure and enhance trailing flames.
• Phosphoric acid does not exhibit this trailing flame enhancement.

Conclusions:

• PCCs effectively inhibit methane diffusion flames, with oxidizer stream addition being superior.
• DMMP and TMP show unique combustion-enhancing effects in the trailing flame due to their methyl groups.
• The study provides insights into flame structure modification by different phosphorus inhibitors.