Characteristic Analysis Of Spraying And Cooling Engine Exhaust System

Ship engines generally have the characteristics of high power and high working load.Therefore,the exhaust gas discharged from the exhaust system is not only bulky and has a high temperature.A large amount of high temperature exhaust gas carries a huge amount of heat.When the smoke enters the atmosphere,it will quickly produce a large area of plume,which will form a strong thermal radiation signal.In order to reduce the heat radiation characteristics of the ship,an exhaust gas cooling and cooling device is usually added to the exhaust system to reduce the exhaust gas temperature of the exhaust system.The addition of an exhaust cooling and cooling device not only reduces the thermal radiation characteristics,but also reduces the pulsation of the exhaust gas,which is beneficial to the reduction of exhaust noise.At present,marine engine exhaust cooling and cooling devices generally include a cold air cooling and a water spray atomizing cooling device.Compared to air cooling,spray water atomization cooling technology requires less cooling medium and higher cooling efficiency.The process and the mechanism of the atomizing-water-cooling technology is very complex,ant it is influenced by many factors.Thanks to the great progress of CFD numerical simulation technology,it provides a feasible simulation analysis method for cooling process.Atomizingwater-cooling process belongs to the gas-liquid two-phase problem with phase transformation process.In order to consider the coupling effect between high temperature flue gas and cooling water droplets,the Euler-Lagrange method is used to describe the computational domain:the flue gas is calculated with the Eulerian frame,and the cooling water droplets are calculated with the Lagrangian frame.Taking into account the turbulent flow,near-wall flow,component transport,droplet force,droplet collision and breakage,this method can reasonably describe the movement process and heat transfer phase transition process of cooling droplets affected by high temperature flue gas flow in exhaust pipe.Based on the analysis of atomizing-water-cooling mechanism,the average diameter of the water droplets is used to value the effect of the atomization.Then,this paper analyses the influence of the effect of the atomization on the cooling process.The results show that the insufficient effect of atomization reduces the heat transfer efficiency,causing the insufficient cooling effect.Compared with the practical atomization effect,a corrective-atomization method is introduced to increase the numerical accuracy.With the corrective-atomization method,the relation between the temperature of flue gas and the flow of cooling water is analysed,and the reason of lower limit temperature of the flue gas at the outlet is obtained.Based on the analysis,the method of further cooling is put forward qualitatively.A variable working condition experimental bench for atomizing-water-cooling system is set up.An external branch tube structure is used to eliminate the interference of droplets on the temperature measurement.Some corresponding experiments are carried out to validate that the numerical methods and numerical results are correct.