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
Methanol is a very promising clean alternative fuel with low carbon content and high octane number,and this makes it well suited to the free-piston engine generator(FPEG)with variable compression ratio characteristics...Methanol is a very promising clean alternative fuel with low carbon content and high octane number,and this makes it well suited to the free-piston engine generator(FPEG)with variable compression ratio characteristics.To the authors’knowledge there are no relevant studies on the application of methanol for FPEG in recent literatures.In this paper,the effects of methanol substitution ratios(MSR)and load ratios on the performances and combustion characteristics of a methane/methanol dual-fuel FPEG have been investigated experimentally and numerically.The results show that the under the gas-liquid two-phase combustion startup strategy,the methane/methanol dual-fuel FPEG can be successfully started and achieve steady operation.Due to higher laminar flame speed(LFS)and the oxygen content of methanol resulting in a faster burning rate,the peak pressure increases by 43.9%from 1.344 MPa for pure methane to 1.934 MPa for 15%of MSR and the corresponding cycle-to-cycle variation decreases from 3.36 to 1.62.The FPEG operating frequency and indicated power gradually increase with the increase of the MSR.Both of them reach maximum values of 34.6 Hz and 193 W at 15%of MSR,which are increased by 19.3%and 49.6%in comparison with the pure methane.However,under specific MSR,both of them decrease with the load ratio increasing because of the large electromagnetic resistance force from the linear generator.CO and CH emissions decrease with the increase of MSR because methanol addition promotes complete combustion of mixture.NOx emissions gradually decrease with MSR increasing owing to the low combustion temperature resulting from the high latent heat of methanol evaporation.The numerical results show that with the increase of MSR,the methane/methanol mixture presents faster flame propagation speed and higher combustion efficiency;while the ignition delay as well as CA10,CA50 and CA90 is significantly shortened due to the increase of active radicals such as H,OH,O and H_(2)O_(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
To develop high energy-density micro power generation systems, a novel two-stroke cycle micro free-piston swing engine (MFPSE), inspired by the concept of the micro internal combustion swing engine, is proposed to sup...To develop high energy-density micro power generation systems, a novel two-stroke cycle micro free-piston swing engine (MFPSE), inspired by the concept of the micro internal combustion swing engine, is proposed to supply mechanical power for a micro power generation system. The working principle, gas exchange and ignition timing control cycles, and structure and operation advantages of the MFPSE are dis- cussed in detail. A prototype where the timing control and geometric parameters are designed with refer- ence to a traditional two-stroke cycle internal combustion engine is fabricated. The successful ignition ex- periment shows that this new concept engine is feasible and is worthy of further study.展开更多
This paper presents a design for a novel,palm sized,high-aspect-ratio engine.To simplify fabrication and keep the device unobtrusive,a design incorporating a two-cycle engine having a flat,rectangular piston with spri...This paper presents a design for a novel,palm sized,high-aspect-ratio engine.To simplify fabrication and keep the device unobtrusive,a design incorporating a two-cycle engine having a flat,rectangular piston with spring return was selected.An experimental engine based on this concept producing a significant amount of useful work was developed.Although results were encouraging,this geometry raised many issues to be investigated and resolved,including the effects of piston sealing,scavenging,heat losses,and combustion efficiency.Due to the complex interplay between these effects,experimental investigation was time consuming and simple models were found to be inadequate.Therefore,a more complex theoretical model accounting for these effects was developed and used to evaluate the sensitivity of engine performance to each of these parameters.The predictions of this model were used to develop recommendations for improving the experimentally developed engine.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
In this paper,the effect of disturbances on the operation process of a methane-fueled free-piston engine generator(FPEG)was experimentally investigated.Four disturbance sources,namely step change of external load,mixt...In this paper,the effect of disturbances on the operation process of a methane-fueled free-piston engine generator(FPEG)was experimentally investigated.Four disturbance sources,namely step change of external load,mixture flow rate fluctuation,random misfire of a cylinder,and elastic collision,were identified and applied to the FPEG.The results showed that the FPEG successfully achieved a steady-state operation with load.The maximum instantaneous electric power of 127 W and the average effective electric power of 38.9 W were obtained.When an external load was instantaneously disconnected,the engine frequency increased from 26.7 Hz to 31.3 Hz.The fluctuation amplitudes of induced voltage,pressure and compression ratio were 18.9%,24.7%and 52.2%respectively in the disturbance.By contrast,when the external load was instantaneously connected,the corresponding values were 42.2%,31.3%and 64.3%respectively,indicating that the instantaneous external load connection had a greater disturbance impact on the FPEG operation stability.Despite encountering the step change of external load,the FPEG can still restore stable operation and show good anti-disturbance ability.Compared with increasing mixture flow rate,reducing the mixture flow rate has a greater disturbance impact on the engine operation stability.Although random misfire of a cylinder will cause remarkable fluctuations in piston displacement and cylinder pressure,the FPEG will not stop running,but continues to work as a single-piston engine.Minor collision event may adversely affect the stability of engine operation,but will not lead to the FPEG shutdown.However,serious collision event may lead to ignition failure and shutdown accident.展开更多
Free-piston engine generators (FPEGs) can be applied as decarbonized range extenders for electric vehicles because of their high thermal efficiency, low friction loss, and ultimate fuel flexibility. In this paper, a p...Free-piston engine generators (FPEGs) can be applied as decarbonized range extenders for electric vehicles because of their high thermal efficiency, low friction loss, and ultimate fuel flexibility. In this paper, a parameter-decoupling approach is proposed to model the design of an FPEG. The parameter-decoupling approach first divides the FPEG into three parts: a two-stroke engine, an integrated scavenging pump, and a linear permanent magnet synchronous machine (LPMSM). Then, each of these is designed according to predefined specifications and performance targets. Using this decoupling approach, a numerical model of the FPEG, including the three aforementioned parts, was developed. Empirical equations were adopted to design the engine and scavenging pump, while special considerations were applied for the LPMSM. A finite element model with a multi-objective genetic algorithm was adopted for its design. The finite element model results were fed back to the numerical model to update the LPMSM with increased fidelity. The designed FPEG produced 10.2 kW of electric power with an overall system efficiency of 38.5% in a stable manner. The model provides a solid foundation for the manufacturing of related FPEG prototypes.展开更多
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 Space Application System of China Manned Space Program.
文摘Methanol is a very promising clean alternative fuel with low carbon content and high octane number,and this makes it well suited to the free-piston engine generator(FPEG)with variable compression ratio characteristics.To the authors’knowledge there are no relevant studies on the application of methanol for FPEG in recent literatures.In this paper,the effects of methanol substitution ratios(MSR)and load ratios on the performances and combustion characteristics of a methane/methanol dual-fuel FPEG have been investigated experimentally and numerically.The results show that the under the gas-liquid two-phase combustion startup strategy,the methane/methanol dual-fuel FPEG can be successfully started and achieve steady operation.Due to higher laminar flame speed(LFS)and the oxygen content of methanol resulting in a faster burning rate,the peak pressure increases by 43.9%from 1.344 MPa for pure methane to 1.934 MPa for 15%of MSR and the corresponding cycle-to-cycle variation decreases from 3.36 to 1.62.The FPEG operating frequency and indicated power gradually increase with the increase of the MSR.Both of them reach maximum values of 34.6 Hz and 193 W at 15%of MSR,which are increased by 19.3%and 49.6%in comparison with the pure methane.However,under specific MSR,both of them decrease with the load ratio increasing because of the large electromagnetic resistance force from the linear generator.CO and CH emissions decrease with the increase of MSR because methanol addition promotes complete combustion of mixture.NOx emissions gradually decrease with MSR increasing owing to the low combustion temperature resulting from the high latent heat of methanol evaporation.The numerical results show that with the increase of MSR,the methane/methanol mixture presents faster flame propagation speed and higher combustion efficiency;while the ignition delay as well as CA10,CA50 and CA90 is significantly shortened due to the increase of active radicals such as H,OH,O and H_(2)O_(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。
基金Supported by the National Natural Science Foundation of China (No. 50375078)
文摘To develop high energy-density micro power generation systems, a novel two-stroke cycle micro free-piston swing engine (MFPSE), inspired by the concept of the micro internal combustion swing engine, is proposed to supply mechanical power for a micro power generation system. The working principle, gas exchange and ignition timing control cycles, and structure and operation advantages of the MFPSE are dis- cussed in detail. A prototype where the timing control and geometric parameters are designed with refer- ence to a traditional two-stroke cycle internal combustion engine is fabricated. The successful ignition ex- periment shows that this new concept engine is feasible and is worthy of further study.
文摘This paper presents a design for a novel,palm sized,high-aspect-ratio engine.To simplify fabrication and keep the device unobtrusive,a design incorporating a two-cycle engine having a flat,rectangular piston with spring return was selected.An experimental engine based on this concept producing a significant amount of useful work was developed.Although results were encouraging,this geometry raised many issues to be investigated and resolved,including the effects of piston sealing,scavenging,heat losses,and combustion efficiency.Due to the complex interplay between these effects,experimental investigation was time consuming and simple models were found to be inadequate.Therefore,a more complex theoretical model accounting for these effects was developed and used to evaluate the sensitivity of engine performance to each of these parameters.The predictions of this model were used to develop recommendations for improving the experimentally developed engine.
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。
基金supported by the National Natural Science Foundation of China(No.52076007)Project of Educational Commission of Henan Province of China(No.22A470007 and No.20A470008)。
文摘In this paper,the effect of disturbances on the operation process of a methane-fueled free-piston engine generator(FPEG)was experimentally investigated.Four disturbance sources,namely step change of external load,mixture flow rate fluctuation,random misfire of a cylinder,and elastic collision,were identified and applied to the FPEG.The results showed that the FPEG successfully achieved a steady-state operation with load.The maximum instantaneous electric power of 127 W and the average effective electric power of 38.9 W were obtained.When an external load was instantaneously disconnected,the engine frequency increased from 26.7 Hz to 31.3 Hz.The fluctuation amplitudes of induced voltage,pressure and compression ratio were 18.9%,24.7%and 52.2%respectively in the disturbance.By contrast,when the external load was instantaneously connected,the corresponding values were 42.2%,31.3%and 64.3%respectively,indicating that the instantaneous external load connection had a greater disturbance impact on the FPEG operation stability.Despite encountering the step change of external load,the FPEG can still restore stable operation and show good anti-disturbance ability.Compared with increasing mixture flow rate,reducing the mixture flow rate has a greater disturbance impact on the engine operation stability.Although random misfire of a cylinder will cause remarkable fluctuations in piston displacement and cylinder pressure,the FPEG will not stop running,but continues to work as a single-piston engine.Minor collision event may adversely affect the stability of engine operation,but will not lead to the FPEG shutdown.However,serious collision event may lead to ignition failure and shutdown accident.
基金the Shanghai Science and Technology Commission(No.19511108500).
文摘Free-piston engine generators (FPEGs) can be applied as decarbonized range extenders for electric vehicles because of their high thermal efficiency, low friction loss, and ultimate fuel flexibility. In this paper, a parameter-decoupling approach is proposed to model the design of an FPEG. The parameter-decoupling approach first divides the FPEG into three parts: a two-stroke engine, an integrated scavenging pump, and a linear permanent magnet synchronous machine (LPMSM). Then, each of these is designed according to predefined specifications and performance targets. Using this decoupling approach, a numerical model of the FPEG, including the three aforementioned parts, was developed. Empirical equations were adopted to design the engine and scavenging pump, while special considerations were applied for the LPMSM. A finite element model with a multi-objective genetic algorithm was adopted for its design. The finite element model results were fed back to the numerical model to update the LPMSM with increased fidelity. The designed FPEG produced 10.2 kW of electric power with an overall system efficiency of 38.5% in a stable manner. The model provides a solid foundation for the manufacturing of related FPEG prototypes.
