A supercharging method for a free piston internal combustion generator

Abstract

The present invention relates to a supercharging method for a free-piston internal combustion generator. By constructing a simulation model of the free-piston internal combustion generator and changing the intake and exhaust pressure values according to different supercharging methods, relationship data one between the intake pressure, exhaust back pressure and the performance parameters of the free-piston internal combustion generator is obtained to determine a matching supercharger. Then, by changing the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe, relationship data two between the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe and the performance parameters of the free-piston internal combustion generator is obtained; the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe of the free-piston internal combustion generator are adjusted. Finally, the adjusted free-piston internal combustion generator is supercharged by using the matching supercharger. Through the supercharging method of the present invention, precise matching between the free-piston internal combustion generator and the supercharger can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system supercharging, and more particularly to a supercharging method for a free piston internal combustion generator. Background Art

[0002] A free piston internal combustion generator is a new type of power device that couples an internal combustion engine with a generator, eliminates the crank - connecting rod mechanism of a traditional internal combustion engine, connects the piston to the mover of a linear generator, and the gas pushes the piston to reciprocate to cut the magnetic induction line, directly converting the chemical energy of the fuel into electrical energy output, greatly shortening the energy transfer chain.

[0003] The free piston internal combustion generator has advantages such as a compact structure, low friction loss, and high energy conversion efficiency, and has good application prospects. However, most of the existing free piston internal combustion engine generators currently adopt the natural aspiration method, resulting in a low power density. While using supercharging technology can effectively improve the power output of the free piston internal combustion generator, randomly selecting a supercharger usually cannot work efficiently, and sometimes it even cannot work, and it is also impossible to ensure that the performance of the free piston internal combustion generator meets the target requirements.

[0004] Therefore, how to provide a supercharging technology for a free piston internal combustion generator to achieve a good match between the free piston internal combustion generator and the supercharger is an urgent problem for researchers in this field. Summary of the Invention

[0005] In view of this, in order to accurately determine the supercharging matching parameters and select a supercharger with a good match for the free piston internal combustion generator to effectively improve the power output of the free piston internal combustion generator, the present invention provides a supercharging method for a free piston internal combustion generator.

[0006] To achieve the above - mentioned purpose, the present invention adopts the following technical solutions:

[0007] A supercharging method for a free piston internal combustion generator includes the following steps:

[0008] S1. Establish a one - dimensional simulation model based on the free piston internal combustion generator and calibrate it;

[0009] S2. According to different supercharging methods, change the boundary pressure values of the intake pressure and the exhaust back - pressure of the one - dimensional simulation model to obtain the performance parameters of the free piston internal combustion generator under different pressures, and determine the relationship data one between the intake pressure, the exhaust back - pressure and the performance parameters of the free piston internal combustion generator;

[0010] S3. Obtain the required intake pressure, exhaust back pressure, and intake air flow according to the target operating conditions of the free piston internal combustion generator and the first set of relationship data. Determine the matching parameters of the supercharger based on the required intake pressure, exhaust back pressure, and intake air flow, and obtain a matched supercharger.

[0011] S4. Change the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe to obtain the second set of relationship data between the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe, and the performance parameters of the free piston internal combustion generator.

[0012] S5. Adjust the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe of the free piston internal combustion generator according to the second set of relationship data to obtain an adjusted free piston internal combustion generator.

[0013] S6. Supercharge the adjusted free piston internal combustion generator using the matched supercharger.

[0014] Preferably, in step S2, different supercharging methods include an electric supercharging method and an exhaust gas turbocharging method.

[0015] In the electric supercharging method, the exhaust back pressure is maintained at a constant value while the intake pressure is changed.

[0016] In the exhaust gas turbocharging method, the air supply ratio and the exhaust gas temperature are kept constant while the exhaust back pressure is changed within a reasonable range.

[0017] Preferably, the performance parameters include effective power, air supply ratio, charge coefficient, fuel consumption rate, and intake and exhaust pressure difference.

[0018] Through the above technical solutions, compared with the prior art, the present invention discloses a supercharging method for a free piston internal combustion generator. By constructing a simulation model of the free piston internal combustion generator, different supercharging methods are simulated to change the intake and exhaust back pressure values, and the relationship data between the intake pressure, exhaust back pressure, and the performance parameters of the free piston internal combustion generator are obtained. Then, in combination with the target operating conditions of the free piston internal combustion generator, the supercharging matching parameters are determined, and a matched supercharger is determined.

[0019] Then, the valve timing, the lengths and diameters of the intake and exhaust pipes are changed to obtain the relationship data between the valve timing, the lengths and diameters of the intake and exhaust pipes, and the performance parameters of the free piston internal combustion generator, which is used to determine the improvement direction of the free piston internal combustion generator after adopting the supercharging technology. Through the supercharging method of the present invention, the precise matching of the free piston internal combustion generator and the supercharger can be achieved. While the performance of the free piston internal combustion generator meets the target requirements, the supercharger can work with a high working efficiency, thereby effectively improving the output power of the generator and achieving a better matching effect between the free piston internal combustion generator and the supercharger. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on the provided accompanying drawings.

[0021] Figure 1 The accompanying drawing is a schematic flow chart of the supercharging method of the free piston internal combustion generator of the present invention;

[0022] Figure 2 The accompanying drawing is a comparison chart of the simulation results and test data of the free piston internal combustion generator prototype of the present invention;

[0023] Figure 3 The accompanying drawing is a change curve graph of the intake pressure of the present invention on the effective power, air supply ratio and charge coefficient of the free piston internal combustion generator;

[0024] Figure 4 The accompanying drawing is a change curve graph of the exhaust back pressure of the present invention on the effective power, fuel consumption rate and intake and exhaust pressure difference of the free piston internal combustion generator;

[0025] Figure 5 The accompanying drawing is a change curve graph of the valve timing of the present invention on the effective power, thermal efficiency, air supply ratio and charge coefficient of the free piston internal combustion generator;

[0026] Figure 6 The accompanying drawing is a change curve graph of the length of the intake and exhaust pipes of the present invention on the charge coefficient of the free piston internal combustion generator;

[0027] Figure 7 The accompanying drawing is a change curve graph of the diameter of the intake pipe of the present invention on the effective power and charge coefficient of the free piston internal combustion generator;

[0028] Figure 8 The accompanying drawing is a matching result graph of the supercharger and the adjusted free piston internal combustion generator of the present invention. Detailed implementation manners

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0030] An embodiment of the present invention discloses a supercharging method for a free piston internal combustion generator. To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with specific embodiments.

[0031] A supercharging method for a free piston internal combustion generator disclosed in this application, as Figure 1 shown, includes the following steps:

[0032] S1. Establish a one-dimensional simulation model according to the free piston internal combustion generator, and calibrate the simulation model based on the test data of the prototype;

[0033] S2. According to different supercharging methods, change the boundary pressure values of the intake pressure and exhaust back pressure of the one-dimensional simulation model to obtain the performance parameters of the free piston internal combustion generator under different pressures, and determine the relationship data one between the intake pressure, exhaust back pressure and the performance parameters of the free piston internal combustion generator;

[0034] S3. According to the target working conditions of the free piston internal combustion generator and the relationship data one, obtain the required intake pressure, exhaust back pressure and intake air flow rate. According to the required intake pressure, exhaust back pressure and intake air flow rate, determine the matching parameters of the supercharger to obtain a matched supercharger;

[0035] S4. Change the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe to obtain the relationship data two between the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe and the performance parameters of the free piston internal combustion generator;

[0036] S5. According to the relationship data two, adjust the valve timing, the lengths and / or diameters of the intake pipe and the exhaust pipe of the free piston internal combustion generator to obtain an adjusted free piston internal combustion generator;

[0037] S6. Use the matched supercharger to supercharge the adjusted free piston internal combustion generator.

[0038] First, in the field of generators, the use of supercharging technology to improve performance has been widely applied. However, if the supercharger used does not match the free-piston internal combustion generator, it will not only fail to improve performance but may even lead to a deterioration in performance. In response to this, the present invention proposes a method for accurately matching the supercharger. Since there is no directly available physical model for the free-piston internal combustion generator, equivalent assumptions need to be made. That is, based on the technical parameters of the free-piston internal combustion generator test prototype and the equivalent assumptions, a one-dimensional simulation model of the free-piston internal combustion generator prototype is built in a one-dimensional simulation software, and the simulation model is calibrated based on the test data of the prototype. Among them, the simulation model includes the intake and exhaust systems, the in-cylinder combustion system, and the piston assembly. The calibration process is as follows: The piston position curve data obtained from the test is imported into the simulation model to simulate the reciprocating motion of the piston assembly in the linear motor, where the mass of the piston assembly includes the mass of the magnetic rod driven by the piston;

[0039] Equivalent assumptions: Since the free-piston internal combustion generator does not have a crank connecting rod mechanism, that is, there is no crank angle in the traditional sense, the time measured in terms of crankshaft angle needs to be converted when establishing the simulation model in the simulation software. The time taken for each cycle of the free-piston internal combustion generator is compared with the 360° of each cycle of a traditional two-stroke engine, and the equivalent crank angle degrees are obtained according to the time ratio. Finally, the operating frequency of the free-piston internal combustion generator needs to be converted into an equivalent rotational speed through Equation (1):

[0040] f = 1 / T = n / 60 (1)

[0041] In Equation (1), f is the operating frequency, with the unit of Hz; T is the cycle time, with the unit of s; n is the equivalent rotational speed, with the unit of r / min.

[0042] Secondly, by changing the boundary pressure values of the intake pressure and the exhaust back pressure, the effects of different supercharging methods on the performance of the free-piston internal combustion generator are simulated, and the performance parameters of the free-piston internal combustion generator under different pressures are obtained.

[0043] Specifically, keeping the exhaust back pressure constant and changing the intake pressure is used to simulate the electric supercharging method;

[0044] When using exhaust gas turbocharging, the presence of the turbine will increase the exhaust back pressure of the free-piston internal combustion generator. Therefore, by keeping the air supply ratio and the exhaust temperature constant and changing the exhaust back pressure within a reasonable range, the exhaust gas turbocharging method is simulated.

[0045] Furthermore, relationship data one between the intake pressure and the exhaust back pressure and the performance parameters of the free-piston internal combustion generator is determined. Among them, the performance parameters of the free-piston internal combustion generator include effective power, air supply ratio, charge coefficient, fuel consumption rate, and intake and exhaust pressure difference.

[0046] Then, based on the target operating conditions of the free piston internal combustion generator and the first set of relationship data, the required intake and exhaust pressures are obtained. According to the required intake and exhaust pressures and the intake air flow rate output by the simulation model, the matching parameters of the supercharger are determined to obtain a matched supercharger. In one embodiment, the geometric dimensions of the supercharger are first determined according to the matching parameters, and then the final matched supercharger is determined.

[0047] It should be noted that directly connecting the matched supercharger to the original free piston internal combustion generator cannot optimize the performance of the free piston internal combustion generator. Because the supercharger is not only an embodiment of supercharging technology but also a component and a machine. Only when the supercharger operates properly can it provide the intake air pressure and intake air flow rate required by the free piston internal combustion generator. Therefore, the original free piston internal combustion generator needs to be adjusted accordingly to match the selected supercharger product.

[0048] The generalized supercharging system not only includes the supercharger itself but also the intake and exhaust pipe lines of the free piston internal combustion generator. It can be seen that the parameters of the intake and exhaust pipe lines have a great impact on the supercharger, and the valve timing controls the intake and exhaust, so it also needs to be considered. In summary, the present invention adjusts the valve timing and the geometric parameters of the intake and exhaust pipes of the free piston internal combustion generator.

[0049] Specifically, by changing the valve timing, the lengths and diameters of the intake and exhaust pipes, the second set of relationship data between the valve timing, the lengths and diameters of the intake and exhaust pipes and the performance parameters of the free piston internal combustion generator is obtained.

[0050] Furthermore, according to the second set of relationship data, the parameters of the free piston internal combustion generator are adjusted, including: according to the second set of relationship data, adjusting the valve timing, the lengths and diameters of the intake and exhaust pipes of the free piston internal combustion generator to better match the selected supercharger and further improve the output power of the generator.

[0051] Finally, the adjusted free piston internal combustion generator is supercharged using the matched supercharger.

[0052] The supercharging method for the free piston internal combustion generator provided by the embodiment of the present invention has simple steps and reasonable setting conditions. It is not necessary to build a supercharger model. Through the simulation supercharging method, both the matching parameters between the free piston internal combustion generator and the supercharger and the transformation direction of the free piston internal combustion generator system after adopting the supercharging technology can be determined, so as to achieve the precise matching between the free piston internal combustion generator and the supercharger.

[0053] In one embodiment, a spark-ignition two-stroke two-cylinder free piston internal combustion generator test prototype is selected as an example for illustration, and its specific technical parameters are shown in Table 1:

[0054] Table 1

[0055] Prototype Features Specific Forms and Parameters Engine Type Two-stroke, Spark Ignition Single-cylinder Engine Displacement / L 0.136 Rated Power Generation / kW 5 Rated Operating Frequency / Hz 30 Design Operating Compression Ratio 8 Scavenging Form Port-Port Type Fuel Supply Form Inlet Manifold Injection

[0056] In the embodiment of the present invention, the test data of the free-piston internal combustion generator prototype at a running frequency of 25 Hz are used to calibrate the established simulation model, and the verification results are referred to Figure 2 , and it can be seen that the simulation model is consistent with the test data during the combustion process, and the maximum error does not exceed 1%. The simulation model can be used for the next step of research.

[0057] Based on this model, different supercharging methods are simulated to change the intake pressure and exhaust back pressure, so as to obtain the performance parameters of the free-piston internal combustion generator under different pressure conditions. Specifically, in this embodiment, at three different running frequencies (25 Hz, 30 Hz, 35 Hz) of the free-piston internal combustion generator, the exhaust back pressure at the outlet environment of the free-piston internal combustion generator is always maintained at 0.108 MPa, the inlet and outlet ambient temperatures are always maintained at 298 K, and the intake pressure changes within the range of 0.12 - 0.19 MPa to simulate the electric supercharging method; the air supply ratio and exhaust temperature are kept constant, and the exhaust back pressure changes within the range of 0.135 - 0.185 MPa to simulate the exhaust gas turbocharging method.

[0058] Furthermore, according to the set intake and exhaust back pressures and the corresponding performance parameters of the free-piston internal combustion generator, the relationship data one between the intake and exhaust back pressures and the performance parameters of the free-piston internal combustion generator is obtained. In this embodiment, the relationship data one, such as Figures 3-4 ,

[0059] First, as Figure 3 , it can be seen that as the intake pressure increases, the effective power of the free-piston internal combustion generator climbs linearly. At a running frequency of 30 Hz and an intake pressure of about 0.18 MPa, the effective power of the free-piston internal combustion generator breaks through 10 kW (target power); thus, the intake pressure can be determined according to the target power. At this time, the intake flow rate of the supercharger can be determined according to the output data of the simulation model under this working condition. In this embodiment, the determined intake flow rate is 0.078 kg / s and the intake pressure is 0.18 MPa.

[0060] As Figure 4Data on the changes in the effective power, fuel consumption rate, and intake and exhaust pressure difference of a free piston internal combustion generator due to changes in exhaust back pressure. As can be seen from the figure, when the operating frequency is 25 Hz, even when the exhaust back pressure reaches 0.185 MPa (the exhaust back pressure cannot be increased indefinitely), the effective power of the free piston internal combustion generator still does not reach the target power, and the fuel consumption rate is also much higher than that of the free piston internal combustion generator operating at 30 Hz and 35 Hz. This is because at low operating frequencies, the amount of gas lost in the short-circuit cycle of the free piston internal combustion generator increases, combustion deteriorates, and the thermal efficiency decreases. This characteristic is more significant under high exhaust back pressure conditions. Generally, the normal range of fuel consumption rate is less than 400 g / (kW·h), and the fuel consumption rate at 25 Hz significantly reaches 500 g / (kW·h). Therefore, it can be concluded that at low operating frequencies, a higher exhaust back pressure will cause the performance of the free piston internal combustion generator to deteriorate comprehensively. Therefore, in this invention, the exhaust back pressure corresponding to the intake pressure is selected as the final exhaust back pressure, and the exhaust back pressure under the target power in this embodiment is 0.108 MPa.

[0061] Furthermore, according to the determined intake pressure, exhaust back pressure, and supercharger intake air flow, determine the matching parameters of the supercharger and select the matching supercharger.

[0062] Then, change the valve timing, the length and diameter of the intake and exhaust pipes of the free piston internal combustion generator in the simulation model, and respectively obtain the second set of change data of the performance parameters of the free piston internal combustion generator due to the changes in valve timing, intake and exhaust pipe length, and diameter, including Figures 5-7 , and adjust and optimize the structure of the free piston internal combustion generator according to the above change data to better match the selected supercharger and achieve supercharging.

[0063] Specifically, in one embodiment, keep the free exhaust time in the simulation model of the free piston internal combustion generator as a fixed value, and use the opening moment of the scavenging valve to characterize the valve timing of the free piston internal combustion generator, and obtain the change data of the effective power, thermal efficiency, air supply ratio, and charge coefficient of the free piston internal combustion generator due to the change in valve timing, as Figure 5 shown. It can be seen that when the opening moment of the scavenging valve is between the two time periods A and B, the effective power and thermal efficiency are inversely proportional. A high effective power will be accompanied by a low thermal efficiency. Therefore, in application, it is necessary to take into account that while the effective power reaches the target, the thermal efficiency cannot be too low, for example, less than 10%. The standard for the high or low thermal efficiency is related to the operating conditions of the free piston internal combustion generator, and specific selection should be based on the actual situation. In this embodiment, the opening moment of the scavenging valve is taken as 29 ms, at which time the thermal efficiency and effective power of the free piston internal combustion generator meet the target requirements while having a suitable air supply ratio and charge coefficient.

[0064] The variation data of the charge coefficient of the free piston internal combustion generator with the change of the intake and exhaust pipe lengths are as follows Figure 6 As shown, it can be seen that there is an optimal intake and exhaust pipe length that enables the free piston internal combustion generator to have a relatively high charge coefficient, and the sensitivity of the charge coefficient to the intake pipe length is higher than that of the exhaust pipe (because the variation range of the charge coefficient with the change of the intake pipe length is greater than that with the change of the exhaust pipe length). The charge coefficient fluctuates greatly with the change of the intake pipe length. With the increase of the exhaust pipe length, the charge coefficient generally shows a downward trend, with small fluctuations in a certain range (500 - 600 mm), but the change amount of the charge coefficient does not exceed 1.4%. Therefore, according to the charge coefficient, the length of the intake and exhaust pipes corresponding to the high charge coefficient is selected as the optimal length. In this embodiment, the optimal length of the intake pipe is 200 mm, and the optimal length of the exhaust pipe is 100 mm;

[0065] The variation data of the effective power and charge coefficient of the free piston internal combustion generator with the change of the intake pipe diameter are as follows. Refer to Figure 7 As can be seen, with the increase of the intake pipe volume, the charge coefficient first increases and then gradually decreases, with a peak value. In the range of pipe diameters from 30 to 50 mm, the charge coefficient decreases by 7.4%, while the power of the free piston internal combustion generator increases by 7.3%. This shows that a high charge coefficient does not necessarily lead to an increase in power. It is necessary to reasonably select the intake pipe diameter. That is to say, while achieving the target power, it is necessary to ensure a relatively high charge coefficient. In this embodiment, the diameter corresponding to the intersection point of the charge coefficient and the effective power is selected as the optimal diameter, that is, the optimal diameter of the intake pipe is 40 mm.

[0066] According to the above analysis, adjust the valve timing, the lengths and diameters of the intake and exhaust pipes of the free piston internal combustion generator

[0067] Finally, use a matched supercharger to supercharge the adjusted free piston internal combustion generator, so that while the performance of the free piston internal combustion generator meets the target requirements, the supercharger can work with a relatively high working efficiency, thereby achieving a better matching effect between the free piston internal combustion generator and the supercharger.

[0068] The matching results of the supercharger and the adjusted free piston internal combustion generator are as follows. Refer to Figure 8 As can be seen, the efficiency of the supercharger exceeds 73% under the rated operating conditions of the free piston internal combustion generator. Under the other operating conditions of the free piston internal combustion generator, the supercharger can work normally and has good surge margin and choke margin (both are greater than 15%). That is to say, the matching between the two is good.

[0069] In the present specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts among the various embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0070] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A supercharging method for a free piston internal combustion generator, characterized in that, It includes the following steps: S1. Establish a simulation model based on the free piston internal combustion generator and calibrate it. The calibration process is as follows: Import the piston position curve data obtained from the test into the simulation model to simulate the reciprocating motion of the piston assembly in the linear motor, where the mass of the piston assembly includes the mass of the magnetic rod driven by the piston; S2. According to different supercharging methods, change the boundary pressure values of the intake pressure and exhaust back pressure of the simulation model, obtain the performance parameters of the free piston internal combustion generator under different pressures, and determine the relationship data one between the intake pressure and exhaust back pressure and the performance parameters of the free piston internal combustion generator; S3. According to the target operating conditions of the free piston internal combustion generator and the relationship data one, obtain the required intake pressure and exhaust back pressure. According to the required intake pressure, the exhaust back pressure, and the intake air flow output by the simulation model, determine the matching parameters of the supercharger and obtain a matched supercharger; S4. Change the valve timing, as well as the length and / or diameter of the intake pipe and exhaust pipe, and obtain the relationship data two between the valve timing, as well as the length and / or diameter of the intake pipe and exhaust pipe and the performance parameters of the free piston internal combustion generator; S5. According to the relationship data two, adjust the valve timing of the free piston internal combustion generator, as well as the length and / or diameter of the intake pipe and exhaust pipe, and obtain an adjusted free piston internal combustion generator; S6. Use the matched supercharger to supercharge the adjusted free piston internal combustion generator.

2. The supercharging method of a free piston internal combustion generator according to claim 1, wherein In step S2, different supercharging methods include electric supercharging method and exhaust gas turbocharging method; The electric supercharging method is to keep the exhaust back pressure constant and change the intake pressure; The exhaust gas turbocharging method is to keep the air supply ratio and exhaust temperature constant and change the exhaust back pressure within a reasonable range.

3. A supercharging method for a free piston internal combustion generator according to claim 1, characterized in that, The performance parameters include effective power, air supply ratio, charge coefficient, fuel consumption rate, and intake and exhaust pressure difference.

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