Low-speed Two-stroke Marine Diesel Engine Emission Control Strategy Based On Exhaust Gas Control And Injection Strategy

The globalization of economical trading has driven the vigorous development of the international transportation industry,and ship transportation has occupied an absolutely important position in international transportation.Increasingly strict environmental regulations put forward higher and higher requirements to ship pollution emissions.Therefore,the importance of achieving pollution control of ship engines is undoubted for economic development.This paper mainly takes marine engine as an example to study the impact of EGR,Miller cycle and fuel injection strategy on emission performance,how much potential of emission reduction can be achieved by combining the three technologies,and how the economic performances of engine are affected by the three technologies.This paper is based on the one-dimensional CFD simulation software GT-Power to analysis by modeling.By contracting EGR module,exhaust control module and fuel injection module to achieve the simulation of EGR,Miller cycle technology and fuel injection strategy technology.The engine Calibration,verification,and simulation are completed based on the engine’s 100% load condition.Based on the verified model,the exhaust gas recirculation module is built,and the exhaust gas in front of the exhaust gas turbine is cooled by the cooling system and then introduced into the intake port.The amount of exhaust gas entering the intake port is controlled by controlling the rotational speed of the mechanical turbine,the quality of each cycle entering the cylinder is constant by controlling the by-pass of intake air.Adopting the above strategies to evaluate the impact of EGR on engine performance,which can achieve effective control of NOx but will cause a sharp rise in soot,and power will also decline to some extent.Three Miller cycle schemes,such as delay of exhaust valve closing time,overall delay of exhaust curve and slope change of exhaust curve closing time,are set in this paper.The optimal Miller cycle scheme is obtained by changing parameters such as air pressure ratio,and the exhaust valve closing timing The comprehensive performance on emission and economy of delaying exhaust valve closing time is slightly better than the other two.The optimal Miller cycle scheme is selected to combine with EGR,which helps to achieve effective control of NOx,but at the same NOx reduction level,more power losses and more soot are generated.In order to modify the sharp increasing of soot,caused by EGR to reduce the NOx,the fuel injection strategy is selected to be combined with EGR.The fuel injection strategy is divided into two types: pilot injection and post injection,which are respectively set as single injection,two injections and four injections except the main injection.By changing the injection quantity and the injection interval angle,theeffect of fuel injection strategy on the combustion performance is realized.Therefore,better emission performance can be obtained.When pilot injection and EGR are combined,NOx and soot are simultaneous reduced,but the reduction is limited and also brings a certain power loss.Because it is started before the main combustion of engine,the internal engine environment can be changed.When post injection and EGR are combined,the soot can be effectively oxidized,which means it can realize the effective control of the soot,but it will cause a certain degree rise of NOx with a certain power loss.Because the fuel is injected after the main injection of the engine is completed.EGR technology is the most efficient means of reducing NOx,but it will lead to an increase of soot,another pollutant.By combing a certain degree of pilot injection and post injection,it is possible to effectively control the comprehensive emission performance of soot and NOx,and achieve a comprehensive improvement in emission performance.