Study On Phenomenological Modeling Of Combustion Process Of Marine Dual Fuel Engine

The main power of ocean-going ships is low-speed two-stroke engine,which mostly uses diesel as fuel.However,with the aggravation of energy shortages and environmental pollution problems in recent years,countries around the world have begun to use natural gas instead of diesel,which makes low-speed two-stroke dual-fuel engines become a research hotspot.At the same time,for large-bore dual-fuel engines,the use of pre-combustion chamber ignition has the advantage of good emission performance,but there are also problems such as knocking and low power output.Therefore,in order to further study and optimize the influence of various parameters on engine performance,it is necessary to establish a combustion model of prechamber dual-fuel engine.The main work of this paper is to establish a phenomenological combustion model in the pre-chamber and the cylinder,and analyze the dual fuel combustion process based on Matlab programming.Firstly,a two-zone phenomenological combustion model is established for the combustion of natural gas in the pre-chamber and the jet flow at the orifice of the pre-chamber.Based on the relationship of mass and energy exchange between the two zones and the established flame propagation law,the equations of mass and energy change of working medium in each zone are determined.At the same time,a phenomenological model for judging the natural shape and expansion of the jet flame based on the Reynolds number at the exit of the orifice is established to determine the jet flow variation trend under ideal conditions.Then based on the natural gas combustion model,a two-zone phenomenological combustion model of pre-chamber dieselignition natural gas engine is established.On this basis,the gas phase jet model of diesel,the expansion of diesel after combustion in the pre-chamber,and the propagation of the pilot flame in the main combustion chamber are considered.It is considered that diesel fuel injected into the pre-chamber is affected by high temperature and high pressure environment,so it expands with gas phase jet,and after a period of ignition delay and entrainment,it burns in a similar condition to the natural gas combustion expansion in the pre-chamber.When the flame is sprayed into the main combustion chamber,the turbulence effect brought by the pilot flame jet is considered.It can be considered that the flame extends outward at a certain turbulent velocity.At the same time,considering that the heat transfer during the entire working process of the actual engine is not negligible,an in-cylinder heat transfer calculation model is added.Finally,a complete calculation model of the pre-chamber dual fuel engine is established.In the process of modeling,Matlab software was used to program according to the designed calculation process.The natural gas combustion model of the pre-chamber was verified.The relative average errors of the calculated and experimental values of the two groups pre-chamber pressure were-4.57% and-0.695%,respectively.The relative average errors of the two groups orifice mass flow rate were-6.862% and-0.738%,respectively.The relative average errors of the two groups ignition flame length were-4.277% and-0.462%,respectively.The results proved the reliability of the model,and the calculation model of the natural gas combustion in the pre-chamber was initially determined.Then for a low-speed two-stroke dualfuel engine,the phenomenological combustion model of the pre-chamber and the main combustion chamber was coupled and modeled.The relative average error of the calculated and experimental value of the main combustion chamber pressure is-1.005%,and the relative average error of the heat release rate of the main combustion chamber is 4.343%.Thus,the feasibility and accuracy of the model were verified.Finally,it provides an effective tool for parametric analysis of combustion process of pre-chamber dual fuel engine.