Study Of Exhaust Manifold Flow Field And Engine Performance On A Turbocharged Gasoline Engine

The stringent emission regulations have been accelerating the evolution of vehicle engine technology.Boosting intake pressure is a technology that is adopted to improve fuel economy by all automobile manufactures,such as the exhaust gas turbocharging technique.Increasing compression ratio is an important approach to enhance engine power,the compression ratio has been increased around 14:1 for gasoline engine in recent years.Although the higher compression ratio can improve the thermal efficiency of gasoline engine,some problem will be arisen because of higher compression ratio,such as knock.For downsizing displacement turbocharged gasoline engine,higher compression ratio would be beneficial to compensate the power loss of engine,because the volume of cylinder was reduced.Generally,the intake temperature and exhaust back pressure of turbocharging engine is higher than that of the natural aspirated engine,which will lead to increase the in-cylinder residual gas fraction(RGF).Undoubtedly,the proper in-cylinder RGF can act as internal EGR that will be beneficial to improve the burn quality,but the excessive RGF maybe deteriorate the combustion and lead to knock.Furthermore,the engine thermal efficiency,mechanical strength will deteriorate due to the excessive in-cylinder RGF.In this paper,it has been focused that the influence of different exhaust manifold characteristic impacted on in-cylinder RGF.In addition,the pulse interference of engine was explained through the flow filed of the exhaust manifold.Firstly,a four-cylinder turbocharged gasoline engine model was built according to the parameters of the 2.0L turbocharged gasoline engine in GT-Power and validated the simulation engine model by bench test dates over 1400-2400r/min,and the difference around 5%.Secondly,the original engine model with one-dimensional exhaust manifold performance was calculated,it was founded that the one-dimensional 4-2-1 exhaust manifold cannot reflect the pulse interference.Based on the conclusion,the coupled model of engine was built(GT-Power coupling FLUENT,the one-dimensional exhaust manifold was displaced by three-dimensional fluid domain)to simulate the engine performance and the flow field of exhaust manifold.It was founded that the coupled simulation can reflect the pulse interference.Theresults reveal the RGF in coupling model is higher than original one-dimensional model.In addition,the 4-2-1 exhaust manifold is more effective in relieving the pulse interference.Meanwhile,there is a phenomenon that is the RGF difference between four cylinders is significant different,the RGF of the first and forth cylinder was very closed,and the others is similar.By analyzing the exhaust manifold flow field,the eddy area is smaller in 4-2-1exhaust manifold and the eddy position is close to the outlet of exhaust manifold.In contrast,in the 4-1 exhaust manifold,the exhaust obstruction is more serious.Lastly,add a bulkhead in 4-2-1exhaust manifold can further reduce the in-cylinder RGF and the RGF between four cylinders is more meaner.Based on this advantage,the spark advance can be further increased to obtain the higher thermal efficiency meanwhile improve the emission.The 1D-3D co-simulation was adopted to explore the in-cylinder RGF,and obtained the RGF tendency of turbocharged engine with different geometry exhaust manifold,and it is presented that the RGF of each cylinder may be not consistent.