Research On Gas Flow Characteristics Of Turbocharged System In Diesel Engine Plateau Environment

The plateau area of our country is vast,with the characteristics of high altitude,wide area and wide range of altitude changes.As an important source of power,diesel engines play an important role in the economic development of plateau areas,transportation and logistics,national defense construction and non-road fields.Turbocharging technology has a certain compensation effect on the increased intake of plateau diesel engines.It is one of the effective means to improve the operating characteristics of plateau diesel engines,and is beneficial to improving the overall operating performance of diesel engines at plateau.The high-altitude working performance of the compressor has an important influence on the overall operating performance of the diesel engine in the plateau environment.The compressor's gas flow efficiency in a plateau environment with a reduced Reynolds number and a lower atmospheric pressure and temperature has deteriorated,resulting in a decline in the performance of the impeller.The performance of the compressor mainly depends on the performance of the turbine.The exhaust gas vortex distribution inside the turbine is reasonable,which can reduce the frictional collision and backflow phenomenon of exhaust gas,reduce the flow loss of exhaust gas,improve the performance of the turbine,and make the compressor have good performance.Therefore,the research on the gas flow characteristics of the turbocharger system under the plateau environment of the diesel engine is carried out,and the flow conditions and flow losses of the turbocharger system at different altitudes are analyzed to provide references for exploring the control measures of the turbocharger flow field and its performance optimization.Taking an off-road two-cylinder diesel engine as the research object,analyzing the operating characteristics of the diesel engine and turbocharging system in plateau environment,obtaining the fluid calculation boundary conditions of the turbocharging system at altitudes of 0m,2000 m,3000m and 4000m;establishing a three-dimensional numerical calculation model of the turbocharging system,Analyze the influence of intake air flow and turbocharger speed on the compressor flow field.Based on the calculation boundary conditions of the supercharging system fluid,carry out the research on the flow characteristics of the supercharging system,and analyze the internal flow conditions and flow losses of the compressor and turbine.Research indicates:(1)Simulation analysis based on altitudes of 0m,2000 m,3000m and 4000 m shows that under high altitude conditions,diesel engine power and torque decrease,effective fuel consumption increases,intake air flow decreases,compressor pressure ratio increases,and efficiency decreases;Compared with 0m,as the altitude increases,the rated operating power of the diesel engine decreases by 1.41%,17.65% and 28.5%,the maximum torque is reduced by 2.99%,10.81% and 19.01%,and the minimum effective fuel consumption rate is increased by 2.23%,5.23%,and 8.08%,and the intake air flow under rated conditions is reduced by 13.25%,21.8%,and 28.3%,respectively.(2)Along the flow path,the pressure and temperature of the compressor impeller increase,and the Mach number first decreases and then increases.As the flow rate increases,the pressure,temperature and Mach number of the compressor impeller decrease,the high entropy area on the meridian surface first decreases and then increases,the low-velocity flow area at the tip clearance position gradually disappears,and supersonic flow appears locally;As the speed of the supercharger increases,the pressure,temperature and entropy from the impeller inlet to the outlet increase,and the impeller inlet Mach number increases,and the meridian surface pressure is relatively high,the high entropy area,the low-speed flow area and the volute section pressure increase.(3)As the altitude increases,the high entropy area of the compressor meridian surface increases,and the impeller outlet pressure decreases;the low-pressure area,high entropy area,and impeller exit wake area on both sides of the splitter blade with 90%blade height increase with the increase in altitude Increase.The pressure,temperature and flow velocity of the compressor impeller section from the inlet to the outlet decreases with the increase in altitude,but the entropy and flow velocity increase.The meridian average entropy increases,and the high-entropy area near the flange extends from the impeller outlet to the leading edge of the blade,and the range is expanded;the high Mach number area in the area with the largest meridian radius increases and extends to the middle of the flow channel;The range of supersonic flow increases,and the range of each blade is inconsistent,and the circumferential direction is uneven.(4)As the altitude increases,the Mach number of the leading edge of the compressor blade is larger,there is a transonic flow area and extends to the blade root,and the shock loss generated increases;the transonic flow area increases,and the pressure between the blade gaps is relatively small,The tip leakage flow is intensified,and part of the gap flow will gradually develop to the middle of the flow channel along the compressor rotation direction,forming a wake and high-entropy zone,and the secondary flow loss will increase,and flow from the impeller outlet to the bladeless diffuser.The mixing loss between the interstitial flow and the mainstream is intensified,and the compressor efficiency is reduced.(5)As the altitude increases,the pressure on the meridian surface of the turbine decreases,and the speed,entropy and temperature increase;the range of the low-velocity flow area at the inlet of the meridian surface and the supersonic flow area at the outlet increases;The entropy area increases;the high temperature area near the entrance of the meridian surface increases with the elevation and extends to the middle of the flow channel.