Simulation Research On The Realization Ways Of Ignited Highly Strengthened Hydraulic Free Piston Engine

The free piston engine has no bearings,no piston lateral force,and the piston motion law has an adaptive relationship with the combustion process.These characteristics indicate the potential of this engine to achieve ultra-high power density.This thesis will demonstrate this potential through simulation,and explore the way to achieve a highly enhanced and efficient spark-ignition hydraulic free piston engine.The simulation establishes a hydraulic free piston engine model that couples the gas combustion gas force in the cylinder with the hydraulic pressure of the piston.It can get rid of the limitation that the piston motion law can only be obtained experimentally,and the simulation of the hydraulic free piston engine is more accurate.After establishing the model and benchmarking with the experiment,the reliability of the model is verified.The hydraulic free piston engine with different supercharging degree and different number of spark plugs is simulated.The characteristics of the piston under the action of hydraulic pressure and combustion gas force are analyzed.On the basis of this,the movement of the engine piston under the equivalence ratio condition is further analyzed.Regularity and combustion process in the cylinder,knocking law and indicating thermal efficiency characteristics.The simulation results show that the moving speed of the piston after accelerating is obviously accelerated,the dwell time is shortened near the top dead center,and the equal tolerance is reduced,so it is more suitable for the case where the ignition phase is higher.The use of multi-point ignition further accelerates the flame propagation speed,and the combustion center of gravity advances,closer to the top dead center,which promotes the improvement of the engine’s isometric capacity,indicating an increase in thermal efficiency.The adaptability of the free piston engine decreases with the increase of the boost ratio,and the multi-point ignition can improve the selfadaptation after boosting.The essence of adaptability is that the center of gravity of the combustion advances with the advance of the ignition phase.The closer the combustion center of gravity CA50 is to the top dead center,the greater the contribution of the gas force generated by the combustion to the piston commutation,and the smaller the compression ratio,which is adaptive.Stronger.Through the calculation of the compression limit compression ratio under different initial pressures,the conclusions about the knocking characteristics of the hydraulic free piston engine and the piston motion law are obtained.Increasing the boost ratio will increase the knock intensity at the same ignition phase.The range of the knock limit compression ratio decreases with the increase of the boost ratio.Under the same boost ratio,the multi-point ignition burst The earthquake tends to increase,but the knock limit compression ratio of multi-point ignition can still reach 14 at the optimal ignition phase.The final research results of this thesis: under the condition of supercharge ratio of 8,through 7-point ignition,the compression ratio is 16.Under the premise of no knocking,45% of the indicated thermal efficiency can be achieved,and the supercharging ratio is 1.In comparison,the power is increased by nearly 7 times,while the indicated thermal efficiency is not reduced.This conclusion points out the direction for the development of ultra-high power density free piston engines.