| Hydraulic free piston engine (HFPE), which converts combustion engine directly to hydraulic energy, represents a viable long-term alternative for an IC engine-hydraulic pump combination. It is such a power unit that perfectly fits hydraulic hybrid drive. HFPE has a simple structure and a variable compression ratio, which makes it suitable for multi-fuel applications. Moreover, hydraulic system is good at energy recovery, thus HFPE particularly suits frequently stop and start walking machines.Based on the four-stroke single piston hydraulic free piston engine test results, the asymmetric motion of the of free piston assembly (FPA) is analyzed. A simulation model is established to study the performance of HFPE. A method of optimization is proposed, which can solve the existing problems. The thesis can be divided into six chapters as follows:In chapter 1, the background and the status of hydraulic free piston engine is introduced. Especially the importance of piston motion and the significance of this study is discussed.In chapter 2, the principle of a four-stroke single-piston hydraulic free piston engine is introduced. Base on the experiment results tested on the test rig, the major research work is proposed.In chapter 3, the dynamics equation of FPA is established to study the asymmetric motion of a single-piston hydraulic free piston engine. The stability of the engine is analyzed.In chapter 4, the simulation model of HFPE is established. The kinematics characteristics, pressure characteristics of the hydraulic chambers are analyzed. External parameters on engine performance are studied.In chapter 5, a method of optimization is obtained. A rack and pinion structure is used to eliminate the overturning moment of FPA, the structure of compression chamber is optimized and the parameters of HFPE are calculated based on energy balance theory.In chapter 6, some conclusions of the research are summarized and future research proposals are suggested. |
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