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A new method for driving the hydraulic free piston engine is proposed. This method achieves the compression stroke automatically rather than special recovery system. Principle of hydraulic differential drive free-piston engine is analyzed and the control strategy of this novel hydraulic driving engine is also introduced. Then energy balance method is used to design the main parameters of the novel engine. High pressure and secondary high pressure of the hydraulic system are constrained by the combustion parameters and therefore parameters are analyzed. In order to verify the effectiveness of energy balance method, the mathematical model is established based on the piston force analysis and engine working principle. The transient results of dynamics are obtained through simulation. In addition, the effectiveness of the simulation is proofed by dimensionless analysis. It indicates that energy balance method realizes the basic performance of hydraulic free piston engine.

In this paper, a new method for the driving of the hydraulic free piston engine (HFPE) is proposed. Hydraulic differential drive achieves the compression stroke automatically rather than special recovery system, which has a great influence on the engine dynamic performance. The purpose of this paper is to solve the key operation and control problems for HFPE to commix fuel with air. HFPE adopts two-stroke loop-scavenging and semi-direct injection. The semi-direct injection nozzle is located in the liner wall inside the main intake port, with the axes oriented towards the piston at the Bottom Dead Center (BDC). Different scavenging pressures and injection angles result in different impacts on the mixture of fuel and air in the cylinder. This study analyzes the changes of the combustion heat release rate by simulation.

In this paper, a new-type balanced opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine is developed by Beijing Institute of Technology. OP2S-GDI engine has some potential advantages such as simple structure, good balance, compact, high power density and thermal efficiency. The structural feature of OP2S-GDI engine leads to the performance difference compared with conventional engines. In order to study and verify the characteristics of this kind of engine, the dynamics characteristics and design scheme of opposed crank-connecting rod mechanism, in-cylinder scavenging process, mixture formation and combustion process are investigated. The influence of parameters on engine performance is investigated, including opposed-piston motion phase difference, intake and exhaust port timing, injection and ignition timing.

The hydraulic free piston engine is a complex mechanical-electro-liquid system, in order to simplify the complex system of the single hydraulic free piston engine, a new method for the driving of hydraulic free piston engine is proposed. Hydraulic differential drive achieves the compression stroke automatically rather than special recovery system. The structure and principle of hydraulic differential drive free-piston engine are analyzed and the mathematical model is established based on the piston force analysis and the hydraulic system working principle. In addition, the control strategy of this novel hydraulic driving engine is also introduced. Finally, the transient results of dynamics are obtained through simulation. Then we compare our results to the ones from the hydraulic free piston engine made by the company Innas.