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Modification and Research of Electronically Controlled Compressed Air Engine Sun Peiyan, Yan Kai, Miao Yang (School of Energy and Power, Dalian University of Technology, Dalian, Liaoning 116023, China) Controlled the conversion of a 4-stroke single-cylinder gasoline engine into a compressed air-powered engine. The modified engine was used to test the engine speed change law by changing the jet pressure and jet pulse width and proposed a new fixed angle control method. The results show that the compressed air engine speed increases with increasing pressure. The jet is sprayed at the left and right positions, and the compressed air utilization is high.
0 rumors In recent years, with the development of modern industry, the energy crisis and pollution problems have become increasingly serious, and clean energy has received more and more attention. Conventional internal combustion engines have pollutant emissions, and current fuel cell technology and electric vehicles are costly and cannot produce market benefits. Therefore, the pursuit of low-pollution or even zero-polluting automotive powerplants has become the goal pursued by designers. The compressed air-powered engine we have described has no combustion process compared with the conventional internal combustion engine. The average effective pressure and pressure rise rate of the engine are low, the engine works smoothly, the noise is low, the material strength is not high, and the manufacturing cost is low. At the same time, the existing mature pneumatic technology can be used to reduce the production and use cost of the engine, which is beneficial to the application and promotion of the compressed air engine. 10. The engine that uses compressed air as the power, the air is the air, which is truly zero pollution.
The principle of the compressed air engine is to use high-pressure air to expand work in the cylinder to replace the combustion expansion process of the conventional internal combustion engine, convert the energy of the compressed air into mechanical energy, and promote the piston movement. Moreover, ordinary internal combustion engines can be converted into air engines. After calculation, the vehicle 300L compressed air with a pressure of 30MPa, under ideal conditions, thermodynamic expansion according to the variable index r=1.2, when converting the compression energy of compressed air into mechanical energy, can drive a car with a mass of 1000kg at a speed 50km/h driving 96km, basically can meet the needs of daily urban traffic. 0. 1 pneumatic engine modification program: Sun Peiyan (1963-), male, Yantai, Shandong, associate professor, this modification uses Lifan LF162MK as a prototype, the basic parameters are shown in the table 1. Usually the ordinary internal combustion engine is converted into a compressed air engine. The research direction is the electric control test of the internal combustion engine. The common method of the T machine is to connect the compressed air directly to the intake port and receive the delivery period: 2011 -03-24 The gas distribution mechanism is modified to change the engine into a two-stroke form. The disadvantage is that the jet is limited by the mechanical structure, and the jet advance angle and jet time cannot be flexibly adjusted according to the engine working conditions, and the engine cannot obtain better economy and power in the whole working condition range. We have less modifications to the original machine, and the engine working process is still 4 strokes. By adopting the method of increasing the sensor and the solenoid valve control, the single-chip microcomputer is used to control the opening and closing of the solenoid valve, and the jet process is precisely adjusted according to the change of the working condition, so that the engine works at an optimal state.
Table 1 LF162MK engine basic parameters project parameters cylinder diameter X non-quantity / mL compression ratio nin1 maximum power / kW - 1 when rated power / kW 1 when the maximum torque / (Nm) 1.1 gas supply and jet control compressed air powered engine power comes from High pressure air. The gas supply system mainly includes a high pressure gas storage tank, a pressure reducing valve and a pressure regulating chamber. The volume of the plenum chamber is designed to be 15 times of the maximum air volume of the air motor working cycle to ensure that the intake pressure is relatively stable. H. The high pressure air is reduced by the pressure of the pressure reducing valve, and then the pressure is stabilized by the tempering chamber, and finally controlled by the single chip microcomputer. The solenoid valve enters the cylinder. Since the prototype is a gasoline engine, the modification method is to process a adapter and install the solenoid valve in the position of the spark plug hole. After receiving the speed and throttle position signals, the MCU controls the working state of the engine by interpolating the calibrated MAP map and outputting control parameters (jet timing, air volume) and injection of compressed air. See the solenoid valve seat and mounting position.
1.2.1 Speed ​​and Position Sensor The prototype uses a non-contact permanent magnet type magnet with a trigger bump on the flywheel, which generates a trigger signal every time the flywheel rotates.
When the boss passes the trigger coil to generate the trigger signal, the crankshaft turns to the top dead center after the crankshaft rotates to the top dead center. After the trigger signal is generated, the crankshaft passes the 30° CA piston to the top dead center. This signal can be used to measure the speed and determine the top dead center position.
1.2.2 Camshaft Position Sensor For ordinary motorcycle engines, one revolution of the crankshaft gives a trigger signal to ignite the igniter. The time difference between the two speed signals can be used to calculate the speed. The 4-stroke gas engine needs to determine the compression top dead center signal, so it is necessary to add a camshaft position sensor to determine whether it is the compression top dead center or the exhaust top dead center. The method we use is to add a sensor to the camshaft so that we get a signal before the compression top dead center. From the above two signals, the position of the crank angle can be judged. The camshaft signal and the crankshaft speed signal are shown in the camshaft signal insertion and exhaust. 1.2.3 Throttle position sensor The throttle position sensor is used to control the duration of the change of the jet, thereby changing the output power of the engine. The voltage dividing circuit is used to change the output voltage between 0 and 5V, and the output voltage signal is filtered and input to the single chip microcomputer.
1.3 Engine Management System 1.3.1 Engine Management System Hardware Design The hardware of the engine management system includes signal processing module, logic circuit module, drive circuit module and power module, which are integrated on one circuit board. The signal processing module is responsible for receiving the signal of the sensor and processing it into a signal that can be read by the microcontroller. The single-chip microcomputer of logic circuit module selects ATmega16 developed by ATMEL as the main chip. It is a low-power, low-voltage, high-performance AVR series microprocessor H. It has rich peripheral interfaces and powerful computing power to meet this topic. Need. After receiving the signal calculation process of the sensor, the single chip microcomputer controls the opening and closing of the electromagnetic valve through the driving circuit.
1.3.2 Engine Management System The software design program adopts C language programming, including signal acquisition, working condition judgment, speed and crank angle position judgment and MAP map module.
When the engine starts, it is judged whether the engine is lower than the idle speed by the rotation speed, and the starting condition is lower than the idle speed. Otherwise, according to the pedal position, the corresponding MAP map is determined to determine the jet time.
Shown is a flow chart of the engine management system program.
2 test results and analysis After the sensor modification and program debugging are completed, enter the engine commissioning phase. At first, because the engine compression ratio is too high, the flywheel's moment of inertia is too small, and the energy generated by the compressed air is not enough to make the crankshaft turn over the compression top dead center, even if The engine cannot be started when the cylinder pressure is increased to 3 MPa. Then, by adding a cylinder head gasket between the cylinder head and the cylinder block, the compression ratio is reduced to 4.8, and the camshaft timing is postponed backward, so that the exhaust valve opens when approaching the bottom dead center, and the intake air is late. The angle of closure increases and closes approximately halfway through the compression stroke, further reducing the actual compression ratio. The engine then started smoothly at 2 MPa jet pressure.
The purpose of the test is to fix the jet advance angle and study the variation of engine performance under different jet pulse widths and jet pressures.
Test procedure: Fix the jet pulse width, adjust the pressure of the pressure reducer, and record the engine speed under different pressures.
Shown is the jet advance angle of 30 °, the jet pulse width is 25, 30, 35, 40, 45 and 50 ms, respectively, the speed changes with pressure when no-load.
At the same jet pulse width, the rotational speed decreases as the jet pressure decreases. When the jet pulse width is 45ms, the stall pressure is the lowest. Because the stop speed is about 720r/min. At this time, the time used for each stroke is 41.67ms, calculated by the jet advance angle = 30°. When the power stroke is different for the jet pulse width, the engine bottom speed changes with the jet pressure. 45ms, in the case of a jet pulse width of 45ms, the amount of compressed air injected into the cylinder is the most before the engine stops, so the engine can be started at a lower pressure.
During the test, the pressure at the outlet of the pressure reducer was adjusted to 2.6 MPa, and the rotational speed did not increase under the condition that the jet pulse width was 25 ms. The reason for the analysis is that the selected solenoid valve opening time is 5 ms. Therefore, the actual injection time is only 20 ms, and although the driving circuit has energized the solenoid valve before the top dead center, the actual opening time of the solenoid valve is already after the top dead center. At this time, the piston starts to descend, and the equal capacity is lowered. The injected high-pressure air cannot establish pressure relatively quickly but expands while spraying, and the energy utilization rate is low. Therefore, although increasing the jet pressure has a tendency to increase the rotational speed, the tendency of such rotational speed increase is offset by the lag of the opening time of the solenoid valve. At this time, if you want to increase the engine speed, increase the pressure and increase the jet advance angle. Taking the curve of the jet pressure of 2. 4MPa as an example, the reason for the analysis is that the crankshaft rotates once in a circle at a speed of 1020r/min for 58.82ms. Under the condition that the jet pulse width is 25ms, the jet process has been calculated. After the 120°CA position after the top dead center, the time for the injection gas to establish pressure and expand is too short. If the jet pulse width is increased again, this part of the gas energy is wasted, so that the jet pulse width is 25ms and 30ms, although The jet time has increased by 1/5, but the speed is basically unchanged. When the jet pulse width is increased again, since the crankshaft has turned past the bottom dead center and starts to ascend, although the exhaust valve has been opened, the injected high-pressure air will hinder the piston from going up, causing the rotation speed to decrease, so when the injection pulse width is greater than 40ms After that, the speed drops instead.
The air motor is different from the expansion process of the ordinary internal combustion engine. The energy of the internal combustion engine comes from the combustion of the fuel. The total mass in the cylinder remains unchanged. When the pneumatic engine is working, the gas carrying the pressure energy passes through the control interface of the cylinder, which is a variable mass system. S. Ordinary internal combustion engine can get more output work during adiabatic expansion. Therefore, when the internal combustion engine is relatively high speed, it is beneficial to reduce heat transfer loss and increase output work. For a pneumatic engine, isothermal expansion can achieve a greater unit mass of available energy S than adiabatic expansion, so at the same jet pressure, lowering the engine speed can increase engine output. Because the lowering of the rotating speed can increase the amount of high-pressure air injected into the engine per unit time, the expansion time increases, and more heat can be absorbed from the outside to increase the available energy. In addition, the suction stroke can introduce heat from the outside.
3 fixed angle control method based on the above test results and analysis, the working process of the air motor is very different from the internal combustion engine. The power of the air motor is determined by the energy of the compressed air entering the cylinder per cycle, while the piston is Downstream injection, due to the reduction of equal capacity, energy waste is very serious, therefore, a new type of pneumatic engine control method is proposed: a certain angle adjustment control method for the crank angle injection pressure regulation control method. The mechanical structure or electronic control is used to control the jet time within a certain angle range before and after the compression top dead center (ie, the fixed crank angle). In this crank angle range, due to the non-uniformity of the crank linkage mechanism movement, the piston stroke The amount of change is not large, and the isometric tolerance in the cylinder is high. The amount of compressed air injected is controlled by adjusting the injection pressure, that is, the load of the engine is directly adjusted by the injection pressure. Such a control method can avoid the waste of energy caused by the reduction of the equal capacity in the cylinder and can reduce the control amount of the engine control system to simplify the control system.
4 Conclusion The prototype is stable after being modified. In the case where the jet advance angle is appropriate, the engine speed increases as the pressure increases. At the top dead center jet, the compressed air utilization rate is higher due to the higher equipotential ratio in the cylinder. In the latter half of the piston, the air volume is very low and the compressed air utilization rate is very low. Therefore, jetting near the top dead center and increasing the injection pressure can improve engine efficiency.
The operation of an aerodynamic engine at low speeds allows more high-pressure air to enter the cylinder and prolongs the time it takes to absorb heat from the outside, which helps to increase the available energy.
When the exhaust valve is opened, the exhaust gas has a certain pressure. Increasing the piston stroke can make the expansion more fully and improve the utilization of the available energy of the compressed air.
In a 4-stroke aerodynamic engine, although the intake stroke and the compression stroke are regarded as completely useless two energy-consuming strokes, the intake stroke can introduce a part of heat from the outside, which is advantageous for the expansion process.
The engine output power torque is very small, there is still a long way to go from practical use, and it needs to be improved.
Chen Ying, Xu Hong, Tao Guoliang, and so on. Research on compressed aerodynamic vehicles with Liu Wei, Zhang Hao, Luo Xinfa, et al. Compressed aerodynamic vehicle integration technology, Yu Xiaoli, Cai Jinlei, and so on. Experimental study on the performance of a pneumatic engine bench. Journal of Zhejiang University, 2006, 40 (1): 135 Yu Xiaoli, Yuan Guangjie, Shen Yuming, and so on. Theoretical analysis of the working cycle of a pneumatic car engine. Journal of Mechanical Engineering, 2002, 38(9): 118-122. (Continued from page 32) 4 Conclusions The harmonic torque amplitude Mv of the small and medium-sized diesel engine is in the third power relationship with the average effective pressure. It can be represented by the corresponding fitting curve.
At present, the simple harmonic coefficient commonly used in large diesel engines is not necessarily suitable for small and medium-sized diesel engines, especially in low harmonics, there may be a large difference, such as low harmonics, and the other harmonics are relatively small.
The phase deviation of the two models is relatively small and can be used for fault diagnosis.
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