Heat Transfer Analysis And Optimization Of The Engine Cooling Jacket Based On Boiling Heat Transfer

The coolant flow and heat transfer affect the engine cooling efficiency,the thermal load of high temperature parts,the heat allocation and the energy utilization.For highly intensified multi-cylinder engines,the cooling uniformity,the intake efficiency,the thermal deformation and the pollution are also influenced by the coolant flow and heat transfer.At high speeds,the subcooled boiling phenomenon occurs in the water jacket,which may affect the cooling of engine.In this paper,a gas-liquid two-phase flow model of boiling heat transfer of engine water jacket is established on the basis of the Mixture multiphase flow in order to study the flow and heat transfer of coolant.According to the simulation results,the water jacket structure of inline 6-cylinder diesel engine is optimized.Mixture multiphase flow model suitable for engine boiling heat transfer is established for the subcooled boiling phenomenon in the engine water jacket under high load conditions.The interphase mass and momentum transfer are introduced into the Mixture multiphase flow model,and two drag models are considered,including the Schiller-Naumann model and the Kelbaliyev-Caylan model.The temperature on the cylinder's fire face of diesel engine is measured under rated speed.Based on the measured data,the accuracies of the single phase model and the multi-phase model are examined.The result shows the Mixture multiphase flow with the Kelbaliyev-Caylan drag model agrees with the tested data better.Based on the Mixture multiphase flow simulation,the effects of the pressure,the velocity,the temperature,the gas distribution and the porosity on the heat transfer of the cooling system are analyzed.The results show that the subcooled boiling phenomenon occurs in the water jacket.Generally,the subcooled boiling benefits the cooling of the water jacket.On the other hand,the subcooled boiling leads to excessive high temperature in the cylinder head enclosed area as well as the top of the block,which makes the coolant flow velocity very low.This may result in a massive pileup of the gas to bring adverse effect on cooling.To solve the bad cooling problem,an optimized design of the water jacket is proposed and a CFD simulation is carried out under the same condition with the initial case.Comparing with the baseline water jacket,the optimized design improves the cooling performance in the cylinder head enclosed area and the top of the block.At the same time,the cooling of other key locations such as the cylinder head nose area remain the same.