Study On Mechanism And Prediction Method Of Carbon Deposit Formation On The Fire Area Of Marine Diesel Engine Cylinder Head

As the power of the ship,marine diesel engine operation in a reliable and stable operation is a core character of it.Carbon deposits on the surface of the cylinder head is under a potentially adverse effect on diesel.Therefore,research on the deposit the cylinder head has practical application value for improving the reliability of the diesel engine.The source and formation process of carbon deposit in the fire area of the marine diesel engine cylinder head was explored.Reduction of carbon deposit on combustion surface of the cylinder head was preliminary studied.Mainly completed the following works:1)Carbon deposit was obtained through 300 hours durability test of an 8-cylinder marine diesel engine.Through comparative analysis of different types of engines,the carbon deposit distribution characteristics of cylinder head combustion area were preliminarily obtained.Carbon deposit samples were analyzed by SEM-EDX,and the composition of carbon deposit was obtained.By identifying the characteristic elements,it is shown that the current deposit on the cylinder head combustion surface mainly comes from fuel,and no correlation with lubricating oil and cooling water.2)Analyze the relationship between the spray process and deposit distribution on combustion area of the cylinder head.A spray test bench for realizing a single injection of a mechanical injector was established for the spray test.Based on the test calibration spray model,through the test and CFD in-cylinder spray flow field analysis,it shows that the current diesel engine spray process does not cause the wet wall phenomenon on the combustion surface of cylinder head,and eliminates the assumption that the cylinder head combustion surface is caused by the wet wall phenomenon.3)Study the relationship between the in-cylinder combustion process and the deposits distribution of the cylinder head.The one-dimensional thermodynamic model of the test diesel engine is used to provide the initial conditions and boundary conditions of the CFD model.The multi-dimensional full-process CFD model of the test diesel engine is established and calibrated,and the results of equivalence ratio distribution,temperature distribution and Soot field distribution in the combustion process were obtained.The analysis showed that the equivalence ratio distribution had a strong correspondence with the carbon distribution of the cylinder head fire area.4)Analysis of the reduction of the deposit area in the cylinder head.The optimized route to reduce the deposit area of the cylinder head was determined,and the nozzle parameters were selected as the research object.Through the evaluation of the carbon distribution in the combustion area of the cylinder head by multiple schemes,one scheme for reducing the deposit area of the cylinder head was selected.This article has the following main conclusions:1.The formation mechanism of the current cylinder area fire area carbon: after the end of the injection,during the post-burning period,the oil mist mixture is guided by the piston combustion chamber profile,and moves to the cylinder head fire surface,accompanied by the cylinder.The eddy current is swept over the surface of the cylinder head.At this time,the oxygen content in the combustion chamber is less,the high-temperature oil mist mixed gas is doped with exhaust gas,Soot,and moves to the cold wall surface to generate quenching effect,and at the same time,the incomplete combustion products are generated,due to the thermophoresis formed by the temperature difference between the gas and the wall surface,Deposited was formed on combustion surface of cylinder head.2.Study the current law of carbon formation in the combustion surface of the diesel engine cylinder head,and establish the current diesel engine cylinder head fire area carbon prediction base: after the end of the injection,the cylinder area fire area carbon is formed within the range of 30 ° CA after the top dead center to the crank angle of the exhaust valve opening.The range of the cylinder head fire surface greater than the equivalent ratio threshold of 0.6 is integrated to form a prediction criterion for the deposits on cylinder head combustion surface.3.Through simulation,verify the influence of multi-nozzle parameters on the charcoal area of the cylinder head.Under the condition that the nozzle outlet area is similar,when the solo factor of the nozzle hole is changed,while the angle between the nozzle orifice increases,the nozzle ofifice diameter decreases,the deposits will reduce in combustion surface of cylinder head.