The structure and working principle of a two-cylinder four-stroke single-piston hydraulic free piston engine(HFPE) were introduced. The basic vibration equation of free piston assembly(FPA) was established based upon ...The structure and working principle of a two-cylinder four-stroke single-piston hydraulic free piston engine(HFPE) were introduced. The basic vibration equation of free piston assembly(FPA) was established based upon the energy conversion between the injected fuel and the friction together with the load. Both the theoretical and numerical results show that the vibration system of FPA is a nonlinear conservative autonomous system in one cycle. The FPA vibration is symmetric with constant amplitude when FPA is only driven by the compression pressure in the compression accumulator and that in the combustion chamber. When considering the friction and load, FPA could still achieve a stable vibration after a few cycles' adjustment whether the input energy is equal to the consumed energy or not. The vibration characteristics are different when FPA vibrates in the compression stroke and the expansion stroke, which is the unique feature of the single-piston HFPE.展开更多
We proposed the flat-type permanent magnet linear alternator (LA) for free piston linear alternators (FPLAs) instead of the tubular one. Using the finite element method (FEM), we compare these two kinds of LAs. The FE...We proposed the flat-type permanent magnet linear alternator (LA) for free piston linear alternators (FPLAs) instead of the tubular one. Using the finite element method (FEM), we compare these two kinds of LAs. The FEM result shows that the flat-type permanent magnet LA has higher efficiency and larger output specific power than the tubular one, therefore more suitable for FPLAs, and that the alternator design can be optimized with respect to the permanent magnet length as well as the air gap.展开更多
The free piston shock tunnel is a type of shock tunnel with high performance. For this type of tunnel, the influence mechanism of shock wave attenuation on tailored operation is explored by numerical simulation and th...The free piston shock tunnel is a type of shock tunnel with high performance. For this type of tunnel, the influence mechanism of shock wave attenuation on tailored operation is explored by numerical simulation and theoretical analysis. By introducing the normalized velocity, the simple constraint equation for shock wave under the tailored operation is deduced. Moreover, the real gas effect is also taken into account in this equation. Based on the equation, the tailored operation of shock tunnels can be predicted with very few calculations. The present study shows that the change rate of the thermodynamic state of the gas behind the shock wave is inconsistent with the attenuation rate of the shock wave, which is the fundamental reason why the wind tunnel achieves tailored operation at a lower Mach number of shock waves. This lower Mach number of shock waves differs from the corresponding ideal value by a factor, which is about the square root of shock attenuation rate.展开更多
In order to clarify the mechanism and main influencing factors of the vibration energy coupling transmission with a dual-piston structure,a thermodynamic and dynamic coupling model of the free piston linear generator(...In order to clarify the mechanism and main influencing factors of the vibration energy coupling transmission with a dual-piston structure,a thermodynamic and dynamic coupling model of the free piston linear generator(FPLG)was established.The system energy conversion,vibration energy coupling transmission,and influencing factors were studied in detail.The coupling transmission paths and the secondary influence mechanism from in-cylinder combustion on vibration energy transmission were obtained.In addition,the influence of the movement characteristics of the dual-piston on the vibration energy transmission was studied,and the typical parameter variation law was obtained,which provides theoretical guidance for the subsequent vibration reduction design of the FPLG.展开更多
Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this paper.The properties,particularly the properties of gas seals of ...Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this paper.The properties,particularly the properties of gas seals of the engine are simulated using a simulation program developed for this case,and the results are utilized in preliminary main design parameter selection.The engine simulation program was developed by combining and modifying the source codes of the simulation and calculation programs obtained from Helsinki University of Technology,Tampere University of Technology,and Lappeenranta University of Technology.Because of the contact-free labyrinth seal used in the piston,the efficiency of the motor is lower than the efficiency of a conventional motor with oil lubricated piston rings.On the other hand,the lack of bearing losses,and the lack of losses associated with a crankshaft system and a gearbox,as well as the lack of lubrication oil expenses,compensates this effect.As a net result,this new motor would perform slightly better than the conventional one.Being completely oil-free,it is very environmentally friendly,and its exhaust gases are completely free of oil residuals which are causing problems in normal gas motors.展开更多
The free-piston engine generator(FPEG)is regarded as the next generation of energy conversion system which may replace traditional engines in the future.The effect of key operational parameters like excess air ratio o...The free-piston engine generator(FPEG)is regarded as the next generation of energy conversion system which may replace traditional engines in the future.The effect of key operational parameters like excess air ratio of input mixture and ignition position on the engine performance of a dual-cylinder FPEG was investigated,and their sensitivity was analyzed in this paper.The operating compression ratio of the system is susceptible to changes in excess air ratio and ignition position.At the same time,it decreases from 15.8 to 6.6 when excess air ratio increases from 0.85 to 1.15,but it increases from 6.1 to 13.3 as ignition position increases from 15 mm to 20 mm.The operating frequency and indicated power are more sensitive to changes in excess air ratio than ignition position.But it is the opposite for the indicated thermal efficiency and friction loss.Excess air ratio and ignition position have a quite similar influence on heat transfer.Therefore,from the perspective of system operation and performance,it is preferable to keep excess air coefficient slightly below 1.0.In contrast,when selecting ignition position,it is of great importance to comprehensively consider the risk of structural damage caused by the increase in the compression ratio and in-cylinder gas pressure.展开更多
This study presents a free piston expander-linear generator (FPE-LG) for engine waste heat recovery.The control strategies based on displacement (control strategy A) and valve timings (control strategy B) are proposed...This study presents a free piston expander-linear generator (FPE-LG) for engine waste heat recovery.The control strategies based on displacement (control strategy A) and valve timings (control strategy B) are proposed.The operation and output characteristics with different control strategies are conducted.The results show that control strategy has significant effect on the FPE-LG performance.When FPE-LG operates with control strategy A,the operation frequency is determined by the intake pressure,advanced exhaust duration,fixed position point and external load resistance,whereas it is only related with the intake/exhaust time and advanced exhaust duration (ta) for control strategy B.The external load resistance has slight influence on the stroke length for these two control strategies.For control strategy A,when advanced exhaust duration is more than 40 ms,the stroke length rises with the intake pressure,whereas it first rises and then reduces when advanced exhaust duration is less than 40 ms.There exist the optimal external load resistance and advanced exhaust duration to achieve the maximum power output with control strategy A,whereas the average power output reduces with the increasing advanced exhaust duration when using control strategy B.Stable operation and high power output can be obtained by using different control strategies and adjusting relevant operation parameters.展开更多
Free piston linear generator(FPLG)is a promising range extender for the electrical vehicle with unparallel advantages,such as compact structure,higher system efficiency,and reduced maintenance cost.However,due to the ...Free piston linear generator(FPLG)is a promising range extender for the electrical vehicle with unparallel advantages,such as compact structure,higher system efficiency,and reduced maintenance cost.However,due to the lack of the mechanic crankshaft,the related piston motion control is a challenge for the FPLG which causes problems such as misfire and crash and limits its widespread commercialization.Aimed at resolving the problems as misfire,a single-piston FPLG prototype has been designed and manufactured at Shanghai Jiao Tong University(SJTU).In this paper,the development process and experimental validation of the related control strategies were detailed.From the experimental studies,significant misfires were observed at first,while the FPLG operated in natural-aspiration conditions.The root cause of this misfire was then identified as the poor scavenging process,and a compressed air source was leveraged to enhance the related scavenging pressure.Afterward,optimal control parameters,in terms of scavenging pressure,air-fuel equivalence ratio,and ignition position,were then calibrated in this charged-scavenging condition.Eventually,the FPLG prototype has achieved a continuous stable operation of over 1000 cycles with an ignition rate of 100%and a cycle-to-cycle variation of less than 0.8%,produced an indicated power of 2.8 kW with an indicated thermal efficiency of 26%and an electrical power of 2.5 kW with an overall efficiency of 23.2%.展开更多
A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equatio...A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equations that are solved simultaneously to predict the performances of the engines. The dynamic analysis performed consists of an evaluation of the frictional force and load force introduced by the generator. The thermodynamic analysis used a single zone model to describe the engine＇ s working cycle which includes intake, scavenging, compression, combustion and expansion, and to evaluate the effect of heat transfer based on the first law of thermodynamics and the ideal gas state equation. Because there is no crankshaft, a time based Wiebe equation was used to express the fraction of fuel burned in the combustion. The calculated results were validated by using the experimental data from another research group. The results indicate that the free-piston generator has some advantages over conventional engines.展开更多
The micro free-piston swing engine （MFPSE） is a new structure, free-piston internal combustion engine. The dynamic model integrated MFPSE with a power generator and thermodynamic models in compression, power and sca...The micro free-piston swing engine （MFPSE） is a new structure, free-piston internal combustion engine. The dynamic model integrated MFPSE with a power generator and thermodynamic models in compression, power and scavenge processes based on the open thermodynamic systems were presented. A simulation was executed at given geometric parameters and initial conditions. The results manifest that the working principle of MFPSE is feasible.展开更多
The compression stroke characteristics of free-piston engine generator were studied. The numerical model of the compression stroke was established based on thermodynamics and dynamics equation,and the leak loss,heat l...The compression stroke characteristics of free-piston engine generator were studied. The numerical model of the compression stroke was established based on thermodynamics and dynamics equation,and the leak loss,heat loss and friction loss were considered. Through solving numerical equations,the in-cylinder pressure of compression stroke under different compression ratios was calculated,energy transfer and conversion process was analyzed,and the calculated results were experimentally verified. The results showed that the actual effective output of electronic energy and the compression energy stored in the com-pressed gas accounted for about 70%. The compression energy gradually increased with the increasing com-pression ratio. When the compression ratio was more than 7. 5,the actual compression energy increased slowly and the energy error between simulation and test decreased.展开更多
为减小重载升沉补偿绞车的体积和转动惯量,提出一种壳动双排柱塞多作用内曲线径向柱塞马达。首先,基于无脉动副角分配方法对马达导轨曲线进行设计;随后,利用Simcenter 3D Motion与AMESim软件构建双马达机械-液压联合仿真模型。仿真结果...为减小重载升沉补偿绞车的体积和转动惯量,提出一种壳动双排柱塞多作用内曲线径向柱塞马达。首先,基于无脉动副角分配方法对马达导轨曲线进行设计;随后,利用Simcenter 3D Motion与AMESim软件构建双马达机械-液压联合仿真模型。仿真结果与理论分析基本吻合,表明马达输出特性符合预期设计目标,同时有效减小了绞车体积和转动惯量。最后,进一步针对相邻马达轴向错位安装角度及柱塞泄漏间隙对输出性能的影响开展仿真分析。相关结论可为升沉补偿绞车的工程设计与优化提供参考。展开更多
针对1 k W以上高功率自由活塞斯特林发电机,本文提出了一种适用于熔融盐、液态金属等外部流体传热的高温换热器结构,并对以液态钠为载热流体、耦合发电机的换热特征进行了仿真和优化。基于发电机氦气侧换热特性,利用计算流体动力学(CFD...针对1 k W以上高功率自由活塞斯特林发电机,本文提出了一种适用于熔融盐、液态金属等外部流体传热的高温换热器结构,并对以液态钠为载热流体、耦合发电机的换热特征进行了仿真和优化。基于发电机氦气侧换热特性,利用计算流体动力学(CFD)仿真考察了槽道结构、进出口管以及载热流体类型等对高温换热器外部载热流体的流动换热特性以及周向流率均匀性的影响。并探究了换热器轴向温度梯度对发电机输出性能的影响。计算结果表明:当液态钠的进口流率为0.7 kg/s(对应换热槽道内的雷诺数为6697)时,结构优化使液态钠的压降由10.32 kPa降低至4.18 kPa,对流换热系数由32.41 k W/(m^(2)·K)增加至34.46 k W/(m^(2)·K),高温换热器内换热槽道的质量流率分布更均匀,0.01∼0.02 kg/s范围内的换热槽道数占总槽道数的75%。高温换热器在轴向上会存在温度梯度,与负温度梯度相比,正温度梯度可将发电机热电效率从28.01%提升至28.15%。展开更多
基金Project(51275451)supported by the National Natural Science Foundation of ChinaProject(51221004)supported by the Science Fund for Creative Research Groups of National Natural Science Foundation of China+1 种基金Project(2013CB035400)supported by the National Basic Research Program of ChinaProject(2011BAK03B09)supported by the National Key Technology R&D Program of China
文摘The structure and working principle of a two-cylinder four-stroke single-piston hydraulic free piston engine(HFPE) were introduced. The basic vibration equation of free piston assembly(FPA) was established based upon the energy conversion between the injected fuel and the friction together with the load. Both the theoretical and numerical results show that the vibration system of FPA is a nonlinear conservative autonomous system in one cycle. The FPA vibration is symmetric with constant amplitude when FPA is only driven by the compression pressure in the compression accumulator and that in the combustion chamber. When considering the friction and load, FPA could still achieve a stable vibration after a few cycles' adjustment whether the input energy is equal to the consumed energy or not. The vibration characteristics are different when FPA vibrates in the compression stroke and the expansion stroke, which is the unique feature of the single-piston HFPE.
基金Project (No. 50806046) supported by the National Natural Science Foundation of China
文摘We proposed the flat-type permanent magnet linear alternator (LA) for free piston linear alternators (FPLAs) instead of the tubular one. Using the finite element method (FEM), we compare these two kinds of LAs. The FEM result shows that the flat-type permanent magnet LA has higher efficiency and larger output specific power than the tubular one, therefore more suitable for FPLAs, and that the alternator design can be optimized with respect to the permanent magnet length as well as the air gap.
基金supported by the National Natural Science Foundation of China (No. 11572303)。
文摘The free piston shock tunnel is a type of shock tunnel with high performance. For this type of tunnel, the influence mechanism of shock wave attenuation on tailored operation is explored by numerical simulation and theoretical analysis. By introducing the normalized velocity, the simple constraint equation for shock wave under the tailored operation is deduced. Moreover, the real gas effect is also taken into account in this equation. Based on the equation, the tailored operation of shock tunnels can be predicted with very few calculations. The present study shows that the change rate of the thermodynamic state of the gas behind the shock wave is inconsistent with the attenuation rate of the shock wave, which is the fundamental reason why the wind tunnel achieves tailored operation at a lower Mach number of shock waves. This lower Mach number of shock waves differs from the corresponding ideal value by a factor, which is about the square root of shock attenuation rate.
文摘In order to clarify the mechanism and main influencing factors of the vibration energy coupling transmission with a dual-piston structure,a thermodynamic and dynamic coupling model of the free piston linear generator(FPLG)was established.The system energy conversion,vibration energy coupling transmission,and influencing factors were studied in detail.The coupling transmission paths and the secondary influence mechanism from in-cylinder combustion on vibration energy transmission were obtained.In addition,the influence of the movement characteristics of the dual-piston on the vibration energy transmission was studied,and the typical parameter variation law was obtained,which provides theoretical guidance for the subsequent vibration reduction design of the FPLG.
基金Project is financed by the Technology Development Center of Finland (Tekes)
文摘Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this paper.The properties,particularly the properties of gas seals of the engine are simulated using a simulation program developed for this case,and the results are utilized in preliminary main design parameter selection.The engine simulation program was developed by combining and modifying the source codes of the simulation and calculation programs obtained from Helsinki University of Technology,Tampere University of Technology,and Lappeenranta University of Technology.Because of the contact-free labyrinth seal used in the piston,the efficiency of the motor is lower than the efficiency of a conventional motor with oil lubricated piston rings.On the other hand,the lack of bearing losses,and the lack of losses associated with a crankshaft system and a gearbox,as well as the lack of lubrication oil expenses,compensates this effect.As a net result,this new motor would perform slightly better than the conventional one.Being completely oil-free,it is very environmentally friendly,and its exhaust gases are completely free of oil residuals which are causing problems in normal gas motors.
基金Projects(51675043,52005038)supported by the National Natural Science Foundation of China。
文摘The free-piston engine generator(FPEG)is regarded as the next generation of energy conversion system which may replace traditional engines in the future.The effect of key operational parameters like excess air ratio of input mixture and ignition position on the engine performance of a dual-cylinder FPEG was investigated,and their sensitivity was analyzed in this paper.The operating compression ratio of the system is susceptible to changes in excess air ratio and ignition position.At the same time,it decreases from 15.8 to 6.6 when excess air ratio increases from 0.85 to 1.15,but it increases from 6.1 to 13.3 as ignition position increases from 15 mm to 20 mm.The operating frequency and indicated power are more sensitive to changes in excess air ratio than ignition position.But it is the opposite for the indicated thermal efficiency and friction loss.Excess air ratio and ignition position have a quite similar influence on heat transfer.Therefore,from the perspective of system operation and performance,it is preferable to keep excess air coefficient slightly below 1.0.In contrast,when selecting ignition position,it is of great importance to comprehensively consider the risk of structural damage caused by the increase in the compression ratio and in-cylinder gas pressure.
文摘This study presents a free piston expander-linear generator (FPE-LG) for engine waste heat recovery.The control strategies based on displacement (control strategy A) and valve timings (control strategy B) are proposed.The operation and output characteristics with different control strategies are conducted.The results show that control strategy has significant effect on the FPE-LG performance.When FPE-LG operates with control strategy A,the operation frequency is determined by the intake pressure,advanced exhaust duration,fixed position point and external load resistance,whereas it is only related with the intake/exhaust time and advanced exhaust duration (ta) for control strategy B.The external load resistance has slight influence on the stroke length for these two control strategies.For control strategy A,when advanced exhaust duration is more than 40 ms,the stroke length rises with the intake pressure,whereas it first rises and then reduces when advanced exhaust duration is less than 40 ms.There exist the optimal external load resistance and advanced exhaust duration to achieve the maximum power output with control strategy A,whereas the average power output reduces with the increasing advanced exhaust duration when using control strategy B.Stable operation and high power output can be obtained by using different control strategies and adjusting relevant operation parameters.
基金supported by the project of Shanghai Science and Technology Commission(No.19511108500).
文摘Free piston linear generator(FPLG)is a promising range extender for the electrical vehicle with unparallel advantages,such as compact structure,higher system efficiency,and reduced maintenance cost.However,due to the lack of the mechanic crankshaft,the related piston motion control is a challenge for the FPLG which causes problems such as misfire and crash and limits its widespread commercialization.Aimed at resolving the problems as misfire,a single-piston FPLG prototype has been designed and manufactured at Shanghai Jiao Tong University(SJTU).In this paper,the development process and experimental validation of the related control strategies were detailed.From the experimental studies,significant misfires were observed at first,while the FPLG operated in natural-aspiration conditions.The root cause of this misfire was then identified as the poor scavenging process,and a compressed air source was leveraged to enhance the related scavenging pressure.Afterward,optimal control parameters,in terms of scavenging pressure,air-fuel equivalence ratio,and ignition position,were then calibrated in this charged-scavenging condition.Eventually,the FPLG prototype has achieved a continuous stable operation of over 1000 cycles with an ignition rate of 100%and a cycle-to-cycle variation of less than 0.8%,produced an indicated power of 2.8 kW with an indicated thermal efficiency of 26%and an electrical power of 2.5 kW with an overall efficiency of 23.2%.
文摘A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equations that are solved simultaneously to predict the performances of the engines. The dynamic analysis performed consists of an evaluation of the frictional force and load force introduced by the generator. The thermodynamic analysis used a single zone model to describe the engine＇ s working cycle which includes intake, scavenging, compression, combustion and expansion, and to evaluate the effect of heat transfer based on the first law of thermodynamics and the ideal gas state equation. Because there is no crankshaft, a time based Wiebe equation was used to express the fraction of fuel burned in the combustion. The calculated results were validated by using the experimental data from another research group. The results indicate that the free-piston generator has some advantages over conventional engines.
基金National Natural Science Foundation(50375078)Key Discipline Construction Program of Beijing.
文摘The micro free-piston swing engine （MFPSE） is a new structure, free-piston internal combustion engine. The dynamic model integrated MFPSE with a power generator and thermodynamic models in compression, power and scavenge processes based on the open thermodynamic systems were presented. A simulation was executed at given geometric parameters and initial conditions. The results manifest that the working principle of MFPSE is feasible.
基金Supported by the National Natural Science Foundation of China(51006010)the Program of Introducing Talents of Discipline to Universities(B12022)
文摘The compression stroke characteristics of free-piston engine generator were studied. The numerical model of the compression stroke was established based on thermodynamics and dynamics equation,and the leak loss,heat loss and friction loss were considered. Through solving numerical equations,the in-cylinder pressure of compression stroke under different compression ratios was calculated,energy transfer and conversion process was analyzed,and the calculated results were experimentally verified. The results showed that the actual effective output of electronic energy and the compression energy stored in the com-pressed gas accounted for about 70%. The compression energy gradually increased with the increasing com-pression ratio. When the compression ratio was more than 7. 5,the actual compression energy increased slowly and the energy error between simulation and test decreased.
文摘为减小重载升沉补偿绞车的体积和转动惯量,提出一种壳动双排柱塞多作用内曲线径向柱塞马达。首先,基于无脉动副角分配方法对马达导轨曲线进行设计;随后,利用Simcenter 3D Motion与AMESim软件构建双马达机械-液压联合仿真模型。仿真结果与理论分析基本吻合,表明马达输出特性符合预期设计目标,同时有效减小了绞车体积和转动惯量。最后,进一步针对相邻马达轴向错位安装角度及柱塞泄漏间隙对输出性能的影响开展仿真分析。相关结论可为升沉补偿绞车的工程设计与优化提供参考。
文摘针对1 k W以上高功率自由活塞斯特林发电机,本文提出了一种适用于熔融盐、液态金属等外部流体传热的高温换热器结构,并对以液态钠为载热流体、耦合发电机的换热特征进行了仿真和优化。基于发电机氦气侧换热特性,利用计算流体动力学(CFD)仿真考察了槽道结构、进出口管以及载热流体类型等对高温换热器外部载热流体的流动换热特性以及周向流率均匀性的影响。并探究了换热器轴向温度梯度对发电机输出性能的影响。计算结果表明:当液态钠的进口流率为0.7 kg/s(对应换热槽道内的雷诺数为6697)时,结构优化使液态钠的压降由10.32 kPa降低至4.18 kPa,对流换热系数由32.41 k W/(m^(2)·K)增加至34.46 k W/(m^(2)·K),高温换热器内换热槽道的质量流率分布更均匀,0.01∼0.02 kg/s范围内的换热槽道数占总槽道数的75%。高温换热器在轴向上会存在温度梯度,与负温度梯度相比,正温度梯度可将发电机热电效率从28.01%提升至28.15%。
