Numerical simulation and experimental study of gas diffusion in a ship engine room

Research on the engine room's natural gas leakage and diffusion has great significance for the LNG Powered ships' design, the fire risk assessment and explosion. In this paper, a model experiment system with a scale ratio of 1:10 was established. Helium gas was used instead of natural gas to study the evolution law of light gas concentration distribution in the model engine room over time. The CFD model of light gas diffusion in the indoor thermal environment is verified by experimental data and used to simulate the natural gas diffusion behavior in a full-size ship's engine room. The influence of leakage amount, cabin temperature, ventilation conditions, leakage location and other factors on the distribution of natural gas concentration was analyzed. The results show that the established CFD model has good predictive power for the diffusion behavior of light gas in the ship's engine room, and the numerical simulation results of the trend of leakage gas concentration with time are consistent with the experiment, and the maximum error is not more than 20%. The amount of leakage has a great influence on the concentration near the leakage location. The larger the initial volume flow and the higher the temperature of the leakage, the larger the dangerous area in the ship's engine room. Increasing ventilation flow is an effective way to reduce the diffusion area and control the concentration of natural gas in the engine room. When the ventilation flow is doubled, the diffusion area of natural gas reduces to 1/3. The leaked natural gas will gather at the location nearing the obstacles which block the jet flow and the upper layer of the engine room. The research results provide a basis for accurately predicting the spatial and temporal distribution model and method of gas diffusion concentration in the engine room environment.