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
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
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
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
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
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
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%。
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.
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.
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.
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。
