The Simulation Research Of High Pressure Ratio Scavenging And Exhaust System Of Marinelow-speed Diesel Engine

Establishing a state of the art prototype with independent intellectual property rights is the key to the realization of domestication of marine low-speed engines.This thesis relies on the high-tech ship research project "low-speed marine engineering" led by CSPI.The turbocharging system of two-stroke low-speed diesel engine as the target engine is researched referring to the typical engine in the project involved.One-dimensional simulation calculation model of the typical engine which is validated with experimental data is established by the simulation software GT-Power after analyzing the structure and features.The simulation calculation model of the target engine is established according to the target specification and the following simulation research was conducted based on the model:(1)The influence of different scavenging port height,scavenging port position,scavenging manifold volume,exhaust manifold volume,and maximum lift of the exhaust valve on the performance of the diesel engine.(2)The influence of different exhaust valve timings,exhaust valve opening gradients,compression ratios,fuel injection starting angles and other adjustable parameters on the performance of the diesel engine,and the exhaust timing and compression ratio were co-simulated.(3)The variable scavenging timing was realized using the sleeve mechanism,and the influence of the variable scavenging timing on the performance of the diesel engine was predicted.The simulation results show that the scavenging port height has a significant influence on the performance of the diesel engine.The scavenging port height needs to have a moderate value.When it is too small,the scavenging effect is insufficient,the residual exhaust gas coefficient is high,the maximum combustion pressure is reduced,and the fuel consumption is increased.Excessively high scavenging port height causes scavenging air to flow back,which also leads to high residual exhaust gas efficiency and high fuel consumption.From the analysis of engine performance at different loads,in the low scavenging port position within limited range,the impact on the engine is small.The one-dimensional model simulation shows that the scavenging receiver volume and the exhaust receiver volume have little effect on the performance of the diesel engine.It is harmful to the exhaust process when the maximum lift of the exhaust valve is too small,which significantly deteriorates the performance of the diesel engine.When the maximum lift of the exhaust valve is higher than a certain level,the change in the maximum lift of the exhaust valve has little effect on the performance of the diesel engine.Compared with the exhaust valve opening timing,the closing timing of the exhaust valve has a significant influence on the performance of the diesel engine.The fuel consumption can be significantly reduced by optimizing the timing of the exhaust valve.In the case of the same exhaust valve opening gradient,the slow closing of the exhaust valve can reduce fuel consumption.With the same closing gradient,the fuel consumption of the quick opening of the exhaust valve is reduced.Low compression ratios do not result in high compression pressures and maximum combustion pressures.Excessive compression ratio can lead to excessively high maximum pressure rise rate and high maximum combustion temperature.The best exhaust valve closing timing and compression ratio were selected through the joint optimization of exhaust valve closing timing and compression ratio.The begin of fuel injection indirectly determines the maximum combustion pressure,so the injection start angle should be selected according to the pressure limit in the cylinder.Diesel engines with variable scavenging timing can use different scavenge heights with different loads and the best scavenging port height is different with different loads.The fuel consumption with asymmetric scavenging timing with different loads is lower than the symmetric scavenging timing with the same scavenging port height.The effects of different scavenging port heights on the asymmetric scavenging timing,different sleeve speed asymmetric scavenging timings,and different scavenging port opening timings under different loads have different effects on the performance of the diesel engine.