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
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
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 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
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
This study investigates the direct impact of heat transfer on the thermodynamic performance of Micro Swing Rotor Engines(MSRE)through numerical analysis.To comprehensively address the influence of heat transfer,we emp...This study investigates the direct impact of heat transfer on the thermodynamic performance of Micro Swing Rotor Engines(MSRE)through numerical analysis.To comprehensively address the influence of heat transfer,we employ a refined thermodynamic simulation model,incorporating a regressive correlation formula,and introduce a fluid-thermal weak coupling method to yield practical solutions.The numerical analysis reveals that heat transfer has profound effects on the performance of MSRE.Specifically,the temperature cycling curve experiences significant alterations,resulting in an increase in cycle-residual mass by 72.6%and a decrease in intake mass by 10.55%at a working frequency of 100 Hz.The pressure cycling curve is primarily affected during the compression and expansion processes,leading to a substantial rise in pressure during compression(reaching1.055 MPa)while the contribution of combustion becomes less noticeable.Consequently,these changes increase engine power consumption during compression by 46.41%and reduce overall engine thermal efficiency by30.23%.Additionally,an increase of the inner wall temperature by 100 K leads to a linear reduction in engine power by 0.1 kW and thermal efficiency by 0.5%.To mitigate these challenges,we propose practical heat management strategies,such as applying heat insulating coatings.The study underscores the critical roles of heat transfer in MSRE operation and provides insights for optimizing its thermodynamic performance,achieving a potential improvement of up to 54.68%in power output and 12.79%in efficiency.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
In this paper,the operation characteristics of a microscale internal combustion swing engine(MICSE)were investigated experimentally and numerically.The energy flow path of MICSE was comprehensively analyzed based on t...In this paper,the operation characteristics of a microscale internal combustion swing engine(MICSE)were investigated experimentally and numerically.The energy flow path of MICSE was comprehensively analyzed based on the first law of thermodynamics.The accuracy of zero-dimensional model was verified by experiments.The indicative thermal efficiency of the engine increases first and then decreases with the increase of equivalent ratio or ignition advance angle.The results show that there exists an optimum equivalent ratio and ignition advance angle during operation.The maximum efficiency of the engine reaches 12.5%when the equivalent ratio and ignition advance angle are 0.8 and−0.553,respectively.MICSE can operate normally when the equivalent ratio is greater than 0.6.The peak value of net heat release rate lags behind that of pressure change,which is different from the conventional crank engine.Experimental and simulation results show that the leakage of MICSE is serious,and it is the main loss of MICSE.The order of energy terms is as follows:leakage loss>exhaust loss>heat loss>indicative work.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
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 (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.
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).
基金supported by the National Basic Research Program of China(Grant No.2014CB239602)the National Natural Science Foundation of China(Grant No.51176072)。
文摘This study investigates the direct impact of heat transfer on the thermodynamic performance of Micro Swing Rotor Engines(MSRE)through numerical analysis.To comprehensively address the influence of heat transfer,we employ a refined thermodynamic simulation model,incorporating a regressive correlation formula,and introduce a fluid-thermal weak coupling method to yield practical solutions.The numerical analysis reveals that heat transfer has profound effects on the performance of MSRE.Specifically,the temperature cycling curve experiences significant alterations,resulting in an increase in cycle-residual mass by 72.6%and a decrease in intake mass by 10.55%at a working frequency of 100 Hz.The pressure cycling curve is primarily affected during the compression and expansion processes,leading to a substantial rise in pressure during compression(reaching1.055 MPa)while the contribution of combustion becomes less noticeable.Consequently,these changes increase engine power consumption during compression by 46.41%and reduce overall engine thermal efficiency by30.23%.Additionally,an increase of the inner wall temperature by 100 K leads to a linear reduction in engine power by 0.1 kW and thermal efficiency by 0.5%.To mitigate these challenges,we propose practical heat management strategies,such as applying heat insulating coatings.The study underscores the critical roles of heat transfer in MSRE operation and provides insights for optimizing its thermodynamic performance,achieving a potential improvement of up to 54.68%in power output and 12.79%in efficiency.
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This project is funded by the National Natural Science Foundation of China(No.52076007)the National Key Basic Research Program of China(No.2014CB239603).
文摘In this paper,the operation characteristics of a microscale internal combustion swing engine(MICSE)were investigated experimentally and numerically.The energy flow path of MICSE was comprehensively analyzed based on the first law of thermodynamics.The accuracy of zero-dimensional model was verified by experiments.The indicative thermal efficiency of the engine increases first and then decreases with the increase of equivalent ratio or ignition advance angle.The results show that there exists an optimum equivalent ratio and ignition advance angle during operation.The maximum efficiency of the engine reaches 12.5%when the equivalent ratio and ignition advance angle are 0.8 and−0.553,respectively.MICSE can operate normally when the equivalent ratio is greater than 0.6.The peak value of net heat release rate lags behind that of pressure change,which is different from the conventional crank engine.Experimental and simulation results show that the leakage of MICSE is serious,and it is the main loss of MICSE.The order of energy terms is as follows:leakage loss>exhaust loss>heat loss>indicative work.
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.
