Study Of Flow Control For Turbine System Of Two-stage Turbocharging Diesel Engine

Two-stage turbocharging technology is an effective approach for diesel engine to realize high power density, energy conservation and CO2 emission reduction. Flow interaction between exhaust manifold and high/low pressure turbine of two-stage exhaust system becomes key factor deciding engine performance because high/low pressure turbine efficiency will be influenced greatly. Besides, the interaction effect is research frontiers of engine fluid mechanics nowadays. So it has significance for engineering need and discipline development that flow interaction effect and influence the effect on performance of engine and two-stage turbines were deeply studied, and flow control method for raising turbine and engine performance was investigated.Parts of two-stage exhaust system were designed respectively at present and flow interaction effect did not be considered. Aiming to the key difficulty, flow interaction mechanism and law were analyzed, based on which flow control approach for exhaust turbine system was proposed to raise performance of two-stage turbines and engine.Flow interaction between exhaust manifold and high pressure turbine was an-alyzed by CFD simulation. Based on the simulation result, changing law of flow with engine working conditions and influence flow interaction on high press-ure turbine flow state and performance were studied. Research result showed tha-t rotor leakage flow moved towards outlet because of inlet multi-swirl distortion structure which strengthened mixing of leakage flow and massage flow and dec-reased t-urbine performance. So a flow control method was proposed, which con-trolled distortion structure at exhaust manifold outlet and raised turbine efficiency further by a new exhaust manifold structure that guiding flow into main pipe t-angentially. Simulation proved that high pressure turbine efficiency can be enhenced by 3.12%.Flow interaction between high pressure turbine and low pressure turbine was analyzed by CFD simulation. Based on the simulation result, changing law of turbine flow with engine working conditions and influence flow interaction on low pressure turbine flow state and performance were studied. Research result showed that inlet swirl brought in crosswise flow in rotor massage which mixed wit-h leakage vortex and decreased turbine performance. So a flow control method was proposed, which controlled crosswise flow in rotor massage and raised low pressure turbine efficiency further by counter-direction design of volutes of two s-tage turbine. Experiment proved that low pressure turbine efficiency can be enhenced by 5.8%.Through-flow model for exhaust turbine system was built which involved flo-w interaction effect in and based on model through-flow analysis method for di esel engine matching was developed. Two-stage exhaust system was optimized aiming to two-stage turbocharged engine full working conditions. Design result pr oved that engine power can be enhanced by 13.35% and specific fuel consumption decreased by 4.6% at rated power point, meanwhile, engine performance keep constant at maximum torque point.