LAUSR

The suppression effectiveness of an intrinsically clean hybrid fire suppressant consisting of nitrogen and water mist was experimentally studied by a cup burner method with methane/air coflowing flame. A series of hybrid agents with different weight ratios of nitrogen and water mist (Sauter mean diameter: 12.6 μm) were tested and compared with nitrogen and water mist used alone. The minimum mass‐based extinction concentration (MEC) of neat nitrogen and water mist was measured as 32.1% and 15.2%, respectively. When combined, MEC of the hybrid agents fell between the limiting values of nitrogen and water mist used alone. An approximately linear relationship was shown for the suppression behavior of nitrogen and water mist in combination. The flow field of suppressants during the flame suppression process was studied by particle imaging velocimetry (PIV) technique. A small portion of water droplets near the flame front evaporated, which contributed to flame extinction by heat absorption and oxygen dilution. The remaining bulk mist was entrained vertically with the air flow, showing little effect on the flame base.