Research On Working Process And Stability Of Hydraulic Free Piston Engine

The hydraulic free piston engine is a kind of novel linear internal combustion engine.The research of hydraulic free piston engine becomes flourishing for its advantages of high efficiency and simplified structure.However,the free state of engine piston brings the challenge of worse cyclic variation and operation stability while the novel idea creates potential advantage.Solving the cyclic variation problem is the precondition of engineering application.Therefore how to make the HFPE operate stably is the current focus and the obstacle in the HFPE field.This article utilizes the combination of experimental method and simulation to address the working process of HFPE.With the analysis of effect of sensitive parameters on the heate release rate,the cyclic engine variation is investigated.The characteristic parameters are obtained by mean of predicting the heat release rate.What's more,the the solution of the nonlinear vibration model is given by the generalized harmonic KBM method.Finally,the hydraulic load control strategy is given based on the stability criterion which is derived from the constant amplitude and the decentration of piston assembly.The main research efforts are following items:1.With the piston force analysis of HFPE,the influence factors of work capacity are investigated.The parameters,such as the injection parameters,scavenging parameters,who affect the work capacity are studied with experimental method and 3D CFD simulation.2.Based on the hydraulic system working principle of HFPE,the hydraulic system is improved.The coupling hydraulic parameters in the improved hydraulic system are analyzed based on the energy balance method.The effectiveness of this designed hydraulic system is verified by the simulation model.3.The effect of the parameters,such as cold starting,injection,intake pressure,working frequency,exhaust valve timing and the hydraulic load,on the heat release rate of HFPE are investigated.The sensibility of these parameters fluctuation are also analyzed.4.The heat release rate of HFPE is fitted by the single Webie function and the double Webie function.The differences of combustion heat release in different cycle are analyzed.The result is that the double Webie function is fit for the combustion heat release rate fitting.5.Support vector machine is fit for the small sample data training and predicting.We utilize this character to train and predict the combustion heat release rate related with the in-cylinder pressure and scavenging time on the special piston position in the compression stroke.Thus the predicting method of combustion heat release rate based on the detection of in-cylinder pressure.6.The forces on the piston assembly are simplified and the nolinear vibration model is established.The expressions of the constant amplitude and the eccentric distance are obtained by the solution of the model.Making use of the unsteady conditions,the relationship of the external input parameters and the stability of the HFPE is built and the parameters variations are also given.7.Taking advantage of the work map based on the in-cylinder detection,which is obtained by the SVM training and predicting,the stable conditions in the next engine cycle is judged.Then the hydraulic load is regulated and controlled.Fianally the corresponding control strategy is established and its effectiveness is also validated by simulation.This article investigates the parameters variations in the HFPE working process.The effect of these parameters on the engine performance is also analyzed.Some efforts have been addressed in the field of stability judging of HFPE.The work supplys for the direction of engine performance optimization and the stability improvement.