Study On Phenomenological Combustion Model For Transient Process Of Marine Diesel Engine

In recent years,increasingly stringent carbon emission regulations have placed high requirements on the energy efficiency of ships.The digital twin technology of marine diesel engines has attracted people’s attention because of its characteristics of improving the energy efficiency of diesel engines.The digital twin technology puts forward requirements for the transient process of the diesel engine combustion model,but most of the transient combustion models in the existing research do not consider the detail combustion process,and cannot reflect the combustion characteristics of the transient process,which is not conducive to the development based on the transient combustion model.Therefore,this article analyzed the combustion phenomenon during transient process,and simplified the partition and mechanism of the combustion model while retaining the core factors that affect combustion.Then a phenomenological combustion model for the transient process of marine diesel engines was established.First,according to the characteristics of the diesel engine combustion process under the transient process,a phenomenological combustion model scheme for the transient process under simplified assumptions was proposed and corresponding model was established.The transient process phenomenological combustion model was based on the one-dimensional discrete spray model which predicted the concentration distribution of fuel in the cylinder,ignoring the process of break-up and atomization,and focusing on the penetration of liquid fuel and air entrainment;an independent simplified turbulence model was built to consider the microscopic effect of turbulent kinetic energy caused by spray on combustion;the average evaporation model and ignition delay model was used to simulate the formation of mixtures.The characteristic time model was used to consider the effect of chemical reaction kinetics and turbulent diffusion on the combustion process and calculate the fuel combustion rate.Then the Fortran language was used to design the program of the transient phenomenological combustion model.The experimental data of constant-volume bomb spray was used to verify the calculation results of the one-dimensional discrete spray model.The phenomenological combustion model was calibrated with the experimental data of 75% load condition of 270 marine medium-speed engine,and the calculation results of cylinder pressure and heat release rate are compared with the experimental data of 50% load condition and 100% load condition.The comparison results show that the average relative error of the cylinder pressure calculation result is less than 3%,and the average relative error of the heat release rate calculation result is less than 5%,which verifies the accuracy of the phenomenological combustion model.The combustion parameters in the phenomenological combustion model were analyzed,and the physical meanings of combustion represented by each part of the sub-models were discussed.The function of the phenomenological combustion model in revealing combustion phenomena is clarified.Finally,a 270 marine turbocharged multi-cylinder diesel engine model was built in GT-Power,and the transient phenomenological combustion model was embedded into the multi-cylinder engine model by co-simulation with Fortran.Then the transient state was set,the simulation results verify that the phenomenological combustion model built in this paper has the ability to reflect the combustion phenomenon in the cylinder during the transient process.