| Modern high power diesel engine have high speed and large fuel injection mass,so it is necessary to complete the fuel injection,crushing,atomization,evaporation and mixing process in a very short time.In order to speed up the formation rate of the mixed gas in the cylinder of the high power diesel engine,improve the uniformity of the mixed gas formation,and improve the combustion process,on the one hand,the fuel injection pressure can be increased and the fuel atomization degree can be increased.On the other hand,it is necessary to reasonably match the shape of the combustion chamber and the fuel injection parameters of the high power diesel engine.This paper takes the high power single-cylinder diesel engine as the research object,improves its power performance based on the improvement of the combustion process,In this paper,AVL-FIRE is used for numerical simulation calculation to study the influence of combustion chamber shape and fuel injection parameters on the performance of high power diesel engines.The main research contents are as follows:(1)This paper first established a simulation calculation model of a single-cylinder high power diesel engine,the initial conditions were obtained through experiment,and the boundary temperature was empirically valued.The simulation cylinder pressure curve is compared with the test cylinder pressure curve,and the maximum error is less than 3%.(2)With the premise of a constant compression ratio,by changing the combustion chamber structure parameters(diameter of the throat,the height of the center-crown,and the depth of the throat),the combustion chambers with different shapes are obtained,and the simulation calculations for each combustion chamber are carried out to analyze the influence of various structural parameters on the combustion process in the cylinder..The results show that appropriately reducing the diameter of the throat and increasing the height of the center-crown can enhance the turbulent motion in the cylinder,improve the combustion,and enhance the power performance.By changing the structure of the combustion chamber,the maximum increase in indicated power compared with the original machine has reached 1.8%.(3)Choose different fuel injection advance angles to simulate in-cylinder combustion,the results show that: As the injection timing advances,the indicated power first increases and then decreases.When the injection advance angle is 14°CA BTDC,the indicated power is the largest,which is 2.2% higher than the original machine.Choosing a suitable fuel injection advance angle can realize the adjustment of the combustion phase,so that the combustion process can be carried out within a reasonable range of crankshaft angle,thereby improving thermal efficiency and power performance.(4)Respectively adjust the nozzle extension height and the angle of the spray to perform simulation calculations.The results show that as the nozzle extension height increases,the power is improved.When the 1.5mm nozzle extension height is used,the power performance is increased by 2.72% compared to the original machine.In general,the change of the nozzle extension height does not greatly improve the power performance;the change of the angle of the spray will lead to the change of the spray axial distribution and the movement trend of the fuel after the wall is hit.The power performance is reduced when the spray angle is too large or too small.When the spray angle is 153°,the indicated power is the largest,which is 2.72%higher than the original machine.(5)When the total flow area of the nozzle holes is constant,the number of nozzle holes is changed for simulation.The results show that the change of the number of nozzle holes will cause the change of the spray circumferential distribution,the penetration distance and the average diameter of Sauter.Too many or too few nozzle holes are not conducive to the improvement of power.When the number of nozzle holes is 12,the indicated power is the maximum,which is 2.72% higher than the original machine. |
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