Research On Transient Temperature Field Distribution Characteristics Of Marine Diesel Engine Combustion In Cylinder

In order to deal with the increasingly stringent emission regulations,improving energy utilization has become one of the most effective measures.The internal combustion engine is developing towards the direction of high power and high thermal efficiency.The research methods of internal combustion engine are also developing.The combustion process of internal combustion engine is the core of the whole working cycle,which directly determines the power,economy and emissions of the engine.The flame temperature field and soot concentration are important indexes to measure the combustion process,which have guiding significance for studying combustion mechanism,improving performance and reducing emissions.There are many methods of non-contact temperature measurement technology,but the general system is more complex,the cost is high,and the ability to adapt to the harsh environment is weak,so it is difficult to realize direct measurement in cylinder,especially continuous measurement in large space scale.Two-color method,as an advanced optical testing method,has the advantages of real-time measurement,high spatial resolution,simple optical path and less signal interference.It can realize large-scale continuous measurement of flame evolution process in time and space,and is widely used in engine combustion process research.At the same time,due to the lack of systematic flame combustion development process and data system of marine diesel engine,the related simulation research can not be carried out without the comparison of boundary condition setting parameters and result data.Therefore,it is necessary to study the transient temperature field and soot concentration field of in-cylinder flame combustion of marine diesel engine by visual method.In this paper,a test system of marine medium and high speed diesel engine is built based on endoscopic visualization technology.The temporal and spatial variation of transient temperature field and soot concentration field of combustion flame in large bore diesel engine under propulsion characteristics was studied.In order to ensure the accuracy of the test results,aiming at the image abnormality of endoscope,the checkerboard calibration method was used to correct it,and the quantitative analysis of the flame area in diesel engine cylinder was realized for the first time.At the same time,the brightness temperature Ta is calibrated by using ultra-high temperature blackbody furnace,and the relationship between the radiation intensity of flame image and temperature is established.It is found that the average temperature of diesel combustion flame is basically a single peak distribution.The combustion temperature of diesel oil rises rapidly to the highest temperature.After that,due to the downward movement of the piston and the vortex movement in the combustion chamber,the temperature dropped.However,because some diesel oil was atomized and burned at this time,the average flame temperature rebounded slightly,but showed a downward trend on the whole.The average flame temperature at 20%load is the highest,followed by 25%.The average flame temperature at 50%load is lower,which is due to the increase of fuel injection at 50%load,the decrease of excess air coefficient,short mixing time and incomplete combustion of diesel oil.At the same time,the higher the load is,the faster the average temperature rises in the early stage of flame combustion.50%load reaches the peak value of flame average temperature at 8.8 CA ATDC,20%and 25%load reaches the peak value of flame average temperature at 9.8 CA ATDC,and15%load rises to the highest temperature at 12.8°CA ATDC.In the early stage of combustion,a large amount of soot was generated,and KL factor increased rapidly to the peak value.After combustion to the later stage,KL factor keeps a level.The oxidation rate of newly generated soot at high temperature is basically the same as that of previously generated soot,with a slight decrease.Among them,the combustion duration of 10%load diesel flame is short,and no new soot is generated in the subsequent combustion.KL factor decreased continuously in the later stage.The KL factor of 20%load is the largest,and the most soot is generated.NO_X emission at 25%load is higher than that at 50%load.It is consistent with the calculated result that the high temperature flame area at 25%load is slightly larger than that at50%.At the same time,the SOOT of 25%load is greater than that of 50%load,which is consistent with the calculated result that the average KL factor under 25%load is greater than that under 50%load.The rationality of the full-text calculation results is proved.