柴油机水下排气管倒流极限试验

Experiment on Zero Liquid Penetration Limits of an Underwater Exhaust Pipe for Marine Diesel Engines

为防止水下排气柴油机发生海水倒灌事故,需弄清水下排气管内海水倒流发生的物理机制与发生条件.通过管内径为90,mm、长度为1.8,m的水平玻璃管在1、2及3,m不同水深下排气的试验,获得了水下排气管倒流极限以及排气口水深变化对其影响.结果表明:在一定排气量范围内水相会在排气管出口端下部稳定地滞留一定长度,但不会形成实质的水倒流;随管内滞留水长度由0增至1.8,m,对应的极限表观气速由24,m/s降至8,m/s,极限Wallis参数由0.95降至0.55,倒流极限呈现出先快速减小后趋于定值的趋势;在相同管内滞留水长度随排气口水深增大,极限表观气速略有减小,而极限Wallis参数基本不变,表明Wallis参数较好地表征了排气密度和排气速度对水下排气管倒流极限的综合影响.

To prevent the seawater backflow accident, it is necessary to clarify the physical mechanism and occurrence condition of the water backflow phenomena in an underwater exhaust pipe for marine diesel engines. By conducting an experiment on the zero liquid penetration （ZLP） limits of an exhaust pipe with the inner diameter of 90 mm and pipe length of 1.8 m under the underwater depths of the gas vent of 1, 2 and 3 m, respectively, the ZLP limits and effect of underwater depth of gas vent on it were obtained. The findings are, under a certain range of gas fows, water phase would stably remain a certain length at the bottom of exhaust pipe near the gas vent in a shape of wedge without the occurrence of real water backflow. As the remaining water lengths in exhaust pipe increase from 0 to 1.8 m, the critical superficial gas velocities and critical gas phase Wallis parameters of the ZLP conditions decrease from 24 m/s to 8 m/s, and from 0.95 to 0.55, respectively, while ZLP limits show the trend of decreasing rapidly at first and then decreasing slowly with the increase of remaining water length. Under the condition of same remaining water length, the critical superficial gas velocity decreases slightly, while the critical gas phase Wallis parameter remains almost unchanged with the increase of underwater depth of gas vent, indicating that the Wallis parameter can well predict the integrated effect of the velocity and density of exhaust gas on the ZLP limit.