Research Of Miller Cycle And Sequential Turbocharging System On Diesel Engine

The technical development of marine diesel engines have always been focused on low emissions,low energy consumption,and high power.Miller cycle technology and sequential turbocharging technology are one of the solutions.The Miller cycle is applied to reduce fuel consumption and NOx emissions.The sequential turbocharging system can supply the engine with sufficient charge air at different loads and make up the insufficient air with Miller cycle.In this paper,the 16 V diesel is set as the research engine,and the simulation model is established with AVL-Boost.Keeping the fuel injection quantity per cycle unchanged,the influence of the Miller cycle of late intake valve closing on engine performance with partial load is studied.The simplified turbocharger model is applied in the simulation.The trapped intake air mass is adjusted constant with different load of the original engine.The influence of intake valve late closing angle on energy balance is analyzed,which includes pumping loss,mechanical friction loss,heat transfer loss and exhaust heat dissipation.The results show that the appropriate late closing angle of the intake valve can reduce the pumping loss,heat transfer loss and exhaust heat dissipation of the diesel engine,improve the power and economy of the diesel engine.The lower the load,the more obvious the improvement.The sequential turbocharging system is easy to cause surge and fluctuate the engine speed when switching,and it is necessary to design a control strategy to ensure the switching process smoothly.In this paper,the 16 V diesel engine is taken as the research object,the steady-state matching of the sequential turbocharging system is carried out through GT-Power,and the switching point of the sequential turbocharging system is determined to be 1600 r/min.The transient simulation model of the diesel engine is used to simulate the cut-in and cut-out process of the controlled turbocharger.The research results show that when the controlled turbocharger is switched in,the air valve is opened 1.5s later than the gas valve,which can effectively avoid the surge of the turbocharger;when the controlled turbocharger is switched out,the air valve and the gas valve are closed at the same time,the turbocharger will not surge.