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
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 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
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
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
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
The power system of a free piston Stirling generator(FPSG)based on potassium heat pipes has been developed in this paper.Thanks to the advantages of long life,high reliability,and high overall thermal efficiency,the F...The power system of a free piston Stirling generator(FPSG)based on potassium heat pipes has been developed in this paper.Thanks to the advantages of long life,high reliability,and high overall thermal efficiency,the FPSG is a promising candidate for nuclear energy,especially in space exploration.In this paper,the recent progress of FPSG based on nuclear reactor for space use was briefly reviewed.A novel FPSG weighted only 4.2 kg was designed,and one dimensional thermodynamic modeling of the FPSG using Sage software was performed to estimate its performance.The experiment results indicated that this FPSG could provide 142.4 W at a thermal-to-electric efficiency of nearly 17.4%.Besides,the power system integrated with four FPSGs and potassium heat pipes was performed and the single machine failure test was conducted.The results show that this system could provide an electrical power of 300 W at an overall thermal efficiency of 7.3%.Thus,it is concluded that this power system is feasible and will have a great prospect for future applications.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
直线发电机作为自由活塞斯特林发电机中实现声–电转换的关键部件,对其开展独立详尽的研究测试具有重要意义。本文基于SAGE软件建立了适用于高温大功率直线发电机动态测试的系统模型,该系统采用对置压缩机作为驱动源,并在模型中引入声...直线发电机作为自由活塞斯特林发电机中实现声–电转换的关键部件,对其开展独立详尽的研究测试具有重要意义。本文基于SAGE软件建立了适用于高温大功率直线发电机动态测试的系统模型,该系统采用对置压缩机作为驱动源,并在模型中引入声学阻抗将压缩机与待测发电机进行高效匹配,进而探究其在不同工况下的动态工作特性。结果表明,在平均压力15 MPa、运行频率70 Hz的额定工况下,为实现待测发电机输出电功18 k W,压缩机总耗功须达到26.8 k W,其中压缩机电–声转换效率为90.5%,热缓冲管中的声功传递效率为86.4%,待测发电机的声–电转换效率为85.9%。通过与实验结果进行对比,验证了计算模型的准确性,本文对于直线发电机动态测试系统的设计工作具有一定的指导意义。展开更多
为解决自由活塞膨胀机的关键部件活塞在高温气体及机械交变载荷下存在的热应力集中、热变形不均及疲劳寿命较低等问题,通过构建几何模型与网格划分,设置流场、热场边界条件,采用热-流-固耦合方法进行有限元分析。结合名义应力法与材料应...为解决自由活塞膨胀机的关键部件活塞在高温气体及机械交变载荷下存在的热应力集中、热变形不均及疲劳寿命较低等问题,通过构建几何模型与网格划分,设置流场、热场边界条件,采用热-流-固耦合方法进行有限元分析。结合名义应力法与材料应力-循环次数(stress-number of cycles,S-N)曲线预测疲劳寿命,发现活塞缓冲区与头部问题显著;进而通过设置环槽、将活塞厚度从10 mm增至20 mm、合理去除活塞中部结构等方式进行结构优化。模拟验证结果表明,优化后活塞热应力降低,局部变形得到有效抑制,疲劳寿命提升,自由活塞膨胀机运行稳定性与可靠性增强,为其实际工程高效应用提供有力支撑。展开更多
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.
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%。
基金supported by the National Natural Science Foundation of China(Grant No.51806227).
文摘The power system of a free piston Stirling generator(FPSG)based on potassium heat pipes has been developed in this paper.Thanks to the advantages of long life,high reliability,and high overall thermal efficiency,the FPSG is a promising candidate for nuclear energy,especially in space exploration.In this paper,the recent progress of FPSG based on nuclear reactor for space use was briefly reviewed.A novel FPSG weighted only 4.2 kg was designed,and one dimensional thermodynamic modeling of the FPSG using Sage software was performed to estimate its performance.The experiment results indicated that this FPSG could provide 142.4 W at a thermal-to-electric efficiency of nearly 17.4%.Besides,the power system integrated with four FPSGs and potassium heat pipes was performed and the single machine failure test was conducted.The results show that this system could provide an electrical power of 300 W at an overall thermal efficiency of 7.3%.Thus,it is concluded that this power system is feasible and will have a great prospect for future applications.
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%.
文摘直线发电机作为自由活塞斯特林发电机中实现声–电转换的关键部件,对其开展独立详尽的研究测试具有重要意义。本文基于SAGE软件建立了适用于高温大功率直线发电机动态测试的系统模型,该系统采用对置压缩机作为驱动源,并在模型中引入声学阻抗将压缩机与待测发电机进行高效匹配,进而探究其在不同工况下的动态工作特性。结果表明,在平均压力15 MPa、运行频率70 Hz的额定工况下,为实现待测发电机输出电功18 k W,压缩机总耗功须达到26.8 k W,其中压缩机电–声转换效率为90.5%,热缓冲管中的声功传递效率为86.4%,待测发电机的声–电转换效率为85.9%。通过与实验结果进行对比,验证了计算模型的准确性,本文对于直线发电机动态测试系统的设计工作具有一定的指导意义。
文摘为解决自由活塞膨胀机的关键部件活塞在高温气体及机械交变载荷下存在的热应力集中、热变形不均及疲劳寿命较低等问题,通过构建几何模型与网格划分,设置流场、热场边界条件,采用热-流-固耦合方法进行有限元分析。结合名义应力法与材料应力-循环次数(stress-number of cycles,S-N)曲线预测疲劳寿命,发现活塞缓冲区与头部问题显著;进而通过设置环槽、将活塞厚度从10 mm增至20 mm、合理去除活塞中部结构等方式进行结构优化。模拟验证结果表明,优化后活塞热应力降低,局部变形得到有效抑制,疲劳寿命提升,自由活塞膨胀机运行稳定性与可靠性增强,为其实际工程高效应用提供有力支撑。
