| With the increasing enhancement of diesel engines,the accompanying sealing problems such as in-cylinder gas leakage and lubricant consumption of piston-ring packcylinder liner friction subsets are becoming more and more significant,and the sealing performance has become one of the serious problems faced by the development of efficient and clean diesel engines.To this end,a high-pressure common rail diesel engine is used as the research object,and a simulation model of piston assembly dynamics is established by combining the temperature field test study.By combining simulation and experiment,the influence of piston assembly structural parameters on the sealing performance of piston-ring set-cylinder liner frictional pair is investigated in depth.The main research contents and conclusions are as follows.(1)A piston assembly dynamics simulation model was established,and the study of the piston dynamics characteristics and sealing performance under the calibration conditions of diesel engine was carried out.The research shows that the piston will change direction and knock several times in one working cycle,thus affecting the sealing performance of the piston assembly,and the peak of knocking energy occurs at 8℃A after the upper stop,which is 0.13N-m.The main peak value of the air fraction exists between 60℃A and 90℃A,and there are two sub-peaks at-60℃A ～-30℃A,and the air fraction of a single cylinder in one working cycle is 15.7L/min.In the in-cylinder lubricating oil consumption path,the wall evaporation accounts for 75.6% and the top ring oil dumping accounts for 22.5%.The friction loss work of the piston reached 54.8k Pa,among which the friction loss work between the main thrust side of the piston and the cylinder liner reached 22.0 kPa.(2)The effects of piston skirt structure,ring bank structure,mating cylinder gap and ellipticity on the sealing performance were investigated.The results show that the change of piston skirt structure changes the inertia force of piston reciprocating motion,which affects the knocking phenomenon between piston and cylinder liner,thus affecting the sealing performance of diesel engine.The change of piston ring bank structure affects the contact state between piston ring and ring groove and changes the gas flow channel in the cylinder,which has a greater impact on the sealing performance of the piston assembly and needs to be considered in the design;among them,when the ring bank chamfer is increased from 0mm to 0.5mm,the maximum increase of gas fraction is 14.9%and the lubricant consumption is increased by 25.7 times.The change of the mating cylinder gap affects the movement of the piston.When the mating cylinder gap increases from 0.065 mm to 0.105 mm,the peak piston knock energy increases by 6.2 times and the lubricant consumption increases by 7.5%.The increase of piston ellipticity will reduce the contact area between piston and cylinder liner,which will increase the second order motion of piston,but the effect on the amount of air movement and lubricating oil consumption is relatively weak.(3)The influence of the structural parameters of the piston ring set on the sealing performance of the diesel engine was studied,and the results showed that: the variation of the structural parameters of the piston ring set has a greater influence on the sealing performance of the diesel engine.Among them: the change of top ring structure greatly affects the amount of oil dumped by the top ring,and the lubricating oil consumption decreases by 24.1% in the process of increasing the reduction of top ring upper end from0.015 mm to 0.035 mm,and the increase of lubricating oil consumption is 53.9% when the trapezoidal angle of top ring increases from 14° to 16°.The change of the second ring structure affects the second ring bank pressure,which has an effect on the amount of air fugitive and lubricant consumption.As the taper angle of the second ring increases,both the amount of air fugitive and the lubricating oil consumption tend to decrease first and then increase;when the thickness of the scraping edge of the second ring increases from 0 to 0.5 mm,the increase of air fugitive and lubricating oil consumption are 6.6%and 17.2% respectively.The change of oil ring structure will affect the movement state of the ring group and have an impact on the sealing performance of the piston assembly,which needs to be taken reasonably in practical engineering applications and should not be too large or too small.The change of piston ring group opening clearance has a significant effect on the air flicking volume,and the top ring and second ring opening clearance have a linear relationship on the air flicking volume of diesel engine,and the oil flicking volume of opening clearance increases when the ring group opening clearance increases.(4)The effect of the structural parameters of the piston assembly on the sealing performance of the diesel engine was analyzed by the response surface method,and the results showed that: among the three factors of piston head clearance,cylinder clearance and ellipticity,the piston head clearance had the greatest effect on the amount of air flick,and the cylinder clearance had the greatest effect on the lubricating oil consumption;among the three factors of top ring upper end reduction,second ring scraping edge thickness and oil ring scraping edge thickness,the second ring scraping edge thickness had the greatest effect on the amount of air flick,and the oil ring scraping edge thickness had the greatest effect on the amount of oil flick.Among the three factors,the thickness of the second ring scraper blade has the greatest influence on the air volume,and the thickness of the oil ring scraper blade has the greatest influence on the lubricating oil consumption. |
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