Simulation Study On Injection Strategy And Scavenging Process Of High Pe Low Speed Diesel Engine

In recent years,ships are becoming larger and larger,and the design value of tonnage and load capacity is greatly improved,which puts forward higher requirements on the power capacity of low-speed diesel engines as the main propulsion device.Therefore,diesel engine manufacturers begin to make the design to enhance the power capacity of original low-speed diesel engines.At present,the most commonly used reinforcement method is to increase the amount of oil injected per cycle and increase the inlet pressure.Since the fuel injection volume and intake pressure of the enhanced low-speed diesel engine are significantly increased,the fuel injection strategy and scavenging process of the original model are no longer applicable,so the fuel injection strategy and scavenging process need to be redesigned.In this paper,through a combination of one-dimensional simulation and three-dimensional simulation,a clear and systematic study of the fuel injection strategy and scavenging process of a enhanced high-Pe low-speed diesel engine is conducted to determine the suitable fuel injection,exhaust timing and three-dimensional structure of the scavenging port.First,using GT-Power software to establish and verify one-dimensional simulation models of injector and diesel engine,and flexibly apply the injector model to simulate different injection models.Study the injection strategy of the target model under rated condition and determine the injection parameters.Secondly,the mathematical method is used to reasonably derive the time-surface value formula of the ideal scavenging port and fit the actual time-surface value curve.Then combined with the determined fuel injection strategy,a one-dimensional simulation study is performed on the area of the scavenging port and the timing of the exhaust valve to determine the relevant parameters.After that,the single-cylinder three-dimensional model was established by UG software,and the one-dimensional simulation calculation results were used as the three-dimensional simulation boundary conditions.The full-cylinder simulation of low-speed diesel engine scavenging port structure was studied using CONVERGE software.The influence of the flow field state finally determines the appropriate structure parameters.Through comparison of the simulation results,it was found that double injection can better improve emissions at the expense of smaller economic performance.It is more suitable for the target engine.The parameters of the double injection has a certain impact on the diesel engine.The orthogonal scheme was used to determine3.5°CA BTDC fuel injection,10%pre-injection rate,4.5°CA pre-main injection interval.After one-dimensional simulation of the scavenging process,it is determined that the area of a single scavenging port is 6465.5mm~2,the height of the scavenging port is 198mm,and the exhaust valve opened at 130°CA ATDC and closed at 295°CA ATDC.Three-dimensional simulations have found that a certain scavenging port elevation angle or radial angle can improve the scavenging and exhausting process,but when the elevation angle or the radial angle is too large,a blind zone of the intake flow will be formed in the cylinder.Finally,the combination of 30°elevation and 0°radial angle of the scavenging port is determined to be suitable for the target diesel engine.