Study On The Process Of Scavenging And Combustion Of Single-cylinder Hydraulic Free Piston Diesel Engine

Hydraulic Free Piston Engine(HFPE)combines internal combustion engine and hydraulic pump to eliminate the plunger drive mechanism of traditional internal combustion engine and hydraulic pump.The piston of the internal combustion engine is connected directly with the plunger of the hydraulic pump through the connecting rod.The fuel chemical energy can directly convert the output to hydraulic energy,reduce the energy conversion steps,reduce energy conversion losses,help improve fuel thermal efficiency,simplify the engine structure,to achieve compact design and flexible power output on engineering machinery and military vehicles.HFPE,as a new type of special internal combustion power plant,which is a multidisciplinary field of internal combustion engine,hydraulic,microelectronics and control,is of great significance to the extensiveness of engineering application prospect and the value of academic research.It has already attracted the attention of international science and technology and achieved rapid technological progress,will bring huge economic and social benefits.HFPE is divided into single piston type,double piston type and opposed piston type according to the piston arrangement structure.In this paper,the basic configuration of single-cylinder single-piston HFPE has been studied.SHFPE has many advantages such as small volume,light weight,low cost,simple structure,few components,wide adaptable fuel,flexible power output and easy realization of PPM mode control,and has a great correlation with opposed piston type HFPE,and the experience of SHFPE can provide some reference for the opposed piston type HFPE.However,the motion and displacement of the SHFPE are susceptible to changes in the force caused by the "freedom" of the piston,and the instability of the scavenging and combustion processes causes the resultant force on the "free piston" to change and touch the piston movement so that SHFPE work stability has been greatly affected,and even lead to abnormal working conditions of the engine.SHFPE can operate stably with a high effectiveness and low emissions,the engine compression ratio,scavenging,fuel injection,combustion for precise control must be studied.Therefore,it is necessary to study the scavenging and combustion process of SHFPE in depth,and try to explore the practical scavenging and combustion methods thatSHFPE can stably work,and analyze its related influencing factors.In this paper,a single-cylinder single-piston hydraulic free piston engine is used as the research object.The main contents are as follows: one is the SHFPE prototype,the second is the SHFPE system characteristic research,and the third is the SHFPE scavenging and combustion process research.In the process of research,some research methods are used such as theoretical research,simulation and test,and apply the research strategy from the overall characteristics of the system to the local characteristics.It is expected that SHFPE system design,SHFPE system performance prediction,SHFPE scavenging structure optimization,SHFPE Combustion process analysis can be get some useful results for the guidance of SHFPE research and development.The basic concept,type and application status of the free piston internal combustion engine are briefly introduced.The development process of the free piston engine is introduced.The research status of HFPE and the key technical problems that need to be explored are introduced.The main research contents of this paper are briefly introduced.The advantages and disadvantages of HFPE with different main structure,power module structure and hydraulic module structure are analyzed by using the contrast method,and the overall technical scheme of the system is determined.The basic working principle of the engine is described.The dynamic simulation model of the system is established by AMEsim,and the dynamic characteristics of the system are simulated.The working performance of SHFPE is studied with the change of main parameters.The relevant simulation data will provide the basis for the design and simulation of scavenging and combustion system.The influence of SHFPE piston motion on the time-area ratio of value of gas port is analyzed.Based on the principle and method of structural design of scavenging system,the method of determining the structure parameters of gas flow in scavenging gas is studied.The influence of the height of the port and the volume of the scavenging chamber on the loop scavenging,the theoretical analysis and numerical simulation of the exhaust dynamic effect are carried out,and the method of comprehensive utilization of Kadenacy effect is put forward.Which laid a foundation for studying the macroscopic scavenging effect and microscopic flow field parameters of SHFPE scavenging structure.The SHFPE prototype designed by the research group is taken as the research object.Based on the special movement law of SHFPE,the CFD software AVL FIRE is used to model and calculate the whole system with inlet,outlet,scavenging passages,scavenging chamber,and combustion chamber.This paper discusses in detail the difference and connection between the hydraulic free piston engine and the traditional crankshaft engine in the scavenging,and analyzes the characteristics of the free-piston engine's loop scavenging and scavenging process,and deeply studies the gas flow parameters that influence the scavenging process and scavenging quality.The ignition delay and heat release model used in AMEsim and FIRE are introduced in detail.Then,the velocity field,concentration field and temperature field of SHFPE compression and combustion process of different combustion chambers are analyzed by AVL FIRE software.The mechanism of the combustion chamber structure on the combustion process is explored,and the microscopic characteristics and macroscopic properties of the combustion process are analyzed.The theoretical basis for the improvement and optimization of the combustion chamber structure is provided.The basic structure and the engine control system part of the hydraulic free piston diesel engine test prototype,and the engine test process work are sorted out.The research contents,main conclusions and innovation points of this paper are sorted out and summarized,and the related work of the next step is analyzed and expected.