Numerical investigation on the vertical jet fire impinging on the horizontal cylindrical obstacle in a ship engine room: Characteristics and new prediction models of flame length

Liquefied natural gas (LNG) serves as a crucial alternative fuel for ships, yet the potential for jet fires arises when compressed natural gas (CNG) is accidently released in a ship engine room. Taking the pipe as the typical cylindrical obstacle, this study conducted a numerical investigation on flame shape characteristics resulting from a vertical jet fire impinging on a horizontal pipe. It is found that both the vertical flame length above the pipe and the horizontal extension flame length underneath it increases with a higher gas leakage velocity. Additionally, a larger pipe diameter was found to suppress the vertical flame length above the pipe while contributing to the horizontal extension length underneath it. Moreover, as increase in the nozzle-pipe distance led to a decrease in both the vertical flame length above the pipe and the horizontal extension flame length. With smaller pipe-nozzle distances and higher gas leakage velocities, more flame spikes were observed above the pipe. To quantify these phenomena, new dimensionless models were developed for the vertical flame length above pipe and the horizontal extension flame length. These models were validated against experimental results, demonstrating deviations within 12.5%. The outcomes of this research can offer an essential reference for fire prevention design, fire risk assessment and fire science research in the engine room of LNG-powered ships.