Study On Mechanism And Performance Of Heavy Oil Combustion In Two-stroke Marine Diesel Engine

In the shipping industry,more than half of the transportation cost is generated by the engine fuel oil cost.With the continuous increase of fuel oil cost,fuel economy has become one of the main factors of the transportation operation cost.Compared with diesel,heavy oil is widely used in marine diesel engines because of its low fuel cost.However,due to the complex composition and poor quality of heavy oil,it is difficult to be fully burned,resulting in a large number of pollutants.With the increasingly strict emission regulations of marine diesel engine,the research on heavy oil combustion mechanism and combustion process has become an important technical approach and research hotspot to realize energy saving and emission reduction of two-stroke marine diesel engine.Considering the high time cycle and material cost of bench test of large marine diesel engine,this paper studies the combustion process and emission performance of heavy oil in marine two-stroke low-speed diesel engine by the method of chemical dynamics model and three-dimensional numerical simulation.Firstly,a numerical simulation alternative fuel for heavy oil is proposed,and a chemical kinetic mechanism model is formed.Then through drgep,sensitivity analysis and reaction path analysis,the simplified mechanism of ignition and combustion of n-dodecane and toluene was established.Secondly,the detailed mechanism and simplified mechanism are used to calculate the ignition delay period of two substances in shock tube and the component concentration in internal combustion engine model,and the experimental data of related literature are compared and analyzed.Finally,a three-dimensional combustion model is built by using the CFD software AVL fire,which is coupled with the simplified mechanism of heavy oil and the dynamic grid model of the combustion chamber.The combustion of heavy oil in the combustion chamber is simulated,and the effect of injection pressure on combustion process and emission is preliminarily studied.The results show that to some extent,increasing the injection pressure is conducive to fuel atomization and oil-gas mixture,making the combustion sufficient and reducing the generation of soot,but it will increase the production of no,that is,there is a contradiction between the production of soot and No.If the injection advance angle is too large,the diesel engine will work rough and no will be generated.Otherwise,if the injection advance angle is too small,the soot emissions will increase.Therefore,it is very important to choose a reasonable injection advance angle for the power and emission performance of the diesel engine.