Numerical Simulation of Liquid-Gas/Gas-Gas Eductors for the Underwater Exhaust System

• Main Authors: Chen, Hsin-Zong, 陳馨宗
• Other Authors: Tsai, Shun-Feng
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/wh26a6

碩士 === 國立臺灣海洋大學 === 輪機工程學系 === 107 === When the exhaust back pressure of the diesel engine is too high, the gas is not smooth. The high exhaust back pressure and low intake vacuum will affect the exhaust and fresh air intake of the diesel engine cylinder, and the combustion process will worsen the diesel engine heat load. The purpose of this thesis is to analyze the diesel engine's underwater exhaustion, and use the aspirator design to simulate and analyze the effects of underwater exhaust and back pressure. Designed at the exhaust manifold or exhaust outlet, using the water jet or the ejector to cause low-pressure exhaust in the exhaust pipe, and then use the expansion effect to increase the pressure of the exhaust to resist the external seawater back pressure, Conducive to the discharge of smoke. In this thesis, the simulation software uses ANSYS Fluent® for the three-dimensional system simulation of water jet/ejective pumping numerical simulation, and the three-dimensional transient compressible flow Navier-Stokes equation, energy equation and VOF(Volume of Fluid) method for the analysis of the aspirator. The turbulence mode uses the Realizable model analogy to turbulent flow. The simulation conditions are based on the goal that the outlet pressure must exceed 1.5 bar (equivalent to 15 m deep exhaust), and the estimated exhaust pressure is 1.3 and 1.2 bar, respectively. The air is vented (6~18 bar) to analyze the exhaust flow ratio that can be taken away. The research results show that the design parameters of the gas aspirator are to be 1.5 bar, and the pressurized air is more than 6 bar. The simulated back pressure of the outlet can reach 1.5 bar or more. The air pressure and flow of the air are required to match and exceed the row. The amount of smoke air does not cause reflux. Although the pressure of the pressurized air is increased, the demand for the flow rate of the pressurized air can be reduced, and the device needs to have sufficient space for the compressed gas to be mixed with the exhaust gas. The water jet is pumped to fix the exhaust back pressure mode, adjust the pressure of the seawater and the diameter of the inflow to adjust the inlet flow. The large diameter with the high water pressure can increase the smoke flow to 1.6 bar, but the excess water required may not be realistic. Happening. Reducing the seawater inflow pipe diameter can still effectively improve the pumping efficiency. In addition to increasing the exhaust gas pressure, the water jet pumping method can be used as a smoke exhaust cooler to reduce the temperature of the smoke stream to avoid the high temperature of the outlet being easily detected.