In order to prevent marine diesel engine from a damage caused by the water pouring back into the diesel from the exhaust pipe

a numerical simulation study was performed on effects of fluctuations in exhaust temperature and exhaust back pressure on the counter current flow limitation in horizontal exhaust pipes. The result indicates that

under the condition of the same exhaust mass flow rate

the increase in exhaust temperature can weaken water backflow in exhaust pipes while the increase in exhaust back pressure can enhance water backflow. In other words

an increased exhaust back pressure can increase the risk of water intrusion accident while an increased exhaust temperature can not. Meanwhile

the result reveales that

in addition to the gas velocity

the properties of exhaust gas

such as the density and viscosity

have a significant influence on the occurrence of water backflow in exhaust pipes. Therefore

it is suggested to consider the effect of exhaust parameter fluctuation on the prevention of water backflow intrusion in the design of exhaust system

and to consider the effect of gas viscosity on the zero liquid penetration point into the prediction model which is often based on a Wallis number that does not include the viscosity of gas.