Simulation Research On The Deposit Formation In The Exhaust Pipe Of The SCR Diesel Engine

With the increasingly stringent emission regulations for heavy-duty diesel engines,the selective catalytic reduction(SCR)technology has become the optimal choice for our country to meet the stricter emission standards.And adblue is widely used as the reductant in SCR system to reduce the nitrogen oxide(NO_x)emission from the diesel engine.But the engine operation condition,exhuaust pipe structure,urea injection system characteristics and environment condition tend to cause the adblue to decompose incompletely,leading to deposits formation in the exhaust pipe,which may result in increased exhaust back pressure and decreased dynamical characteristic,fuel economic characteristic,reliability of the engine.The researches on the deposit formation in the exhaust pipe of the SCR diesel engine have been widely conducted and two kinds of models have been proposed:the deposit formation model based on the exhaust pipe flow field and the deposit reaction mechanism model based on the thermogravimetric tests.But both of the existing models can't study the deposit mass quantitatively,thus it's hard to provide accurate and effective support for reducing or avoiding deposits.In order to solve above problem,a stage IV diesel engine with 11.12 L displacement which equiped with SCR aftertreatment is used as an example to set up a model for quantitatively calculating the deposit mass in the exhaust pipe through simulations and experiments.Then based on this model simulation studies on the factors of the deposit are carried out and the impact law of the factors on the deposit mass is obtained.The main contents and conclusions are as follows:(1)Based on the AVL FIRE and BOOST software,a model is established to quantitatively calculate the deposit mass under variable boundry conditions by linking the CFD model of the exhaust pipe with the deposit reaction mechanism model.Then the model parameters are analyzed and identified by the engine bench test results,and the error of the model is limited to±10%.(2)By using the model,the impact of the factors including the engine operation conditions,exhuaust pipe structure parameters,urea injection system parameters and environment conditions on the deposit mass is analyzed.The results show that:the deposit mass is changed along with the heat conductivity of exhaust pipe in a manner of logarithmic regularity and it's changed along with exhaust temperature,convective heat transfer coefficient of the environment in a manner of parabolic regularity,and there is linear relationship between the deposit mass and other factors.