STUDY ON THE INFLUENCE OF MULTI-FREQUENCY NOISE ON THE COMBUSTION CHARACTERISTICS OF POOL FIRES IN SHIP ENGINE ROOMS

Abstract

A large amount of low- and medium-frequency noise can be found in the engine room of a ship. However, during the development of a fire, vibrations of the air in the engine room at different frequencies can be caused by noise disturbances, and the flow field distribution in the flame zone will be changed, which will affect the combustion characteristics of the pool fire. In this paper, an n-heptane pool with a diameter of 6 cm in a confined space of 1500 mm × 1500 mm × 1000 mm is used. The effects of noise of 75 dB, 90 dB, 105 dB, and 112 dB at 250 Hz, 700 Hz, and 1000 Hz and the noise of the engine room on the combustion behavior of the pool fire are studied experimentally. The results of the analysis of the variation in fuel mass, flame height, and flame tilt show that the multi-frequency noise significantly affects the combustion characteristics of the pool fire in a confined space. Under the perturbation of noise waves, the fuel mass flux of the pool is larger than that of the pool fire when it burns freely, and the fuel mass flux is exponentially nonlinearly related to the noise pressure. In general, the flame height gradually decreases with an increasing noise pressure in the engine room. Additionally, a new coupling relationship between the flame height and the noise pressure is established based on the noise motion equation, and it is found that there is a negative exponential between the noise pressure and the flame height. In addition, the flame can tilt under the action of the air particle displacement caused by the noise of the engine room. The noise pressure field formed in the confined space has a restraining effect on the pool fire, and the flame tilt angle gradually decreases with an increasing noise pressure.