Research On The Influence Of Sequential Turbocharging System On The Performance Of A Yacht Engine

The matching of engine and turbocharger usually takes the rated condition as the reference standard,namely,when the engine is in the rated condition,the efficiency of the turbocharger is high and the booster effect is good.While in the low load condition,the exhaust gas flow and energy are relatively low,which makes the efficiency declined,lacking air inflow of engine and worsening in-cylinder combustion.For this purpose,using sequential turbocharging system(STC)to improve engine performance at low load and start research.The STC system in this paper has two turbochargers,one is a basic turbocharger,the other is a controlled turbocharger,the controlled turbocharger has a pneumatic butterfly valve on its each side.The STC system controls the cut-in and cut-out of the controlled turbocharger by controlling the opening and closing of the butterfly valve.The cut-in and cut-out process of the controlled turbocharger has a great influence on the operation of the engine and the two turbocharger,so the switching process of the controlled turbocharger is the key point of this study.The switching process of controlled turbocharger is studied through two methods:simulation modeling and experiment.Simulation modeling: first,simulating the whole working process of the engine;then,establishing the simulation model of original machine by the software named GT-Power and verify the model.Then,the simulation model of sequential turbocharging system is built based on this model,Then,setting up the simulation model of the STC system based on this model and finally we simulated making advantage of this simulation model.Experimental research: according to the design requirements,the turbocharging system of the original machine is transformed,and then the corresponding tests are carried out.First,the yacht engine was tested in the state of 1TC(only the basic turbocharger work)and the 2TC(both basic and controlled turbocharger work),and then the switching process of the controlled turbocharger was tested.The results show that the performance of the engine at low load can be effectively improved by the sequential turbocharging system,and the economy is improved(the maximum drop of oil consumption is 4.77%),and the emissions also have a great improvement(the maximum emission reduction of carbon smoke is 16.2%).However,the sequential turbocharging system(the STC system)has little effect on the engine when it is under the high load condition.In charge and discharge switching process of controlled turbocharger,the time differencebetween the opening and closing of the air valve and the gas valve is called switching delay time.Through the simulation,the switching point of 1TC to 2TC is 50% load,the speed is 1191r/min,the reasonable switching delay time in the cut-in process is 1 ~ 2s,and the reasonable switching delay time in the cut-out process is 0s.Through the experiment,we can draw that the best switched operating point from 1TC to 2TC is 40% load,revolving speed is 1105r/min,and the optimal switching delay time in the cut-in process is 1s,and the best switching delay time in the cut-out process is 0s.The experiment shows that the optimal switching delay time has the least influence on the yacht engine and the turbocharger in the switching process,the yacht engine has a good emission of carbon smoke,the turbocharger will not surge,the switching process is stable,and the performance indexes of the engine are good.