自由活塞发动机的活塞运动规律优化与试验

林继铭; 徐照平; 闫皓

doi:10.3969/j.issn.1002-6819.2015.06.012

自由活塞发动机的活塞运动规律优化与试验

1.
华侨大学机电及自动化学院，厦门 361021
2.
南京理工大学机械工程学院，南京 210094

基金项目: 国家自然科学基金资助项目（51207071）；中国博士后科学基金特别资助（2012T50476）；华侨大学科研基金资助项目（15BS103）。

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出版历程
- 收稿日期: 2014-12-15
- 修回日期: 2015-03-03
- 发布日期: 2015-03-14

Optimization and experiment on piston motion law of four-stroke free-piston engine

1.
College of Mechanical Engineering and Automation, Huaqiao University, Xiamen 361021, China
2.
School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China

摘要

摘要: 为了提高四冲程、点燃式自由活塞发动机系统的输出效率，该文在分析其工作原理的基础上，设定边界约束和路径约束，建立了活塞运动规律优化模型。基于系统工作过程中活塞分阶段运行的特性，采用高斯伪谱法离散状态与控制变量，将活塞运动规律优化问题离散化为非线性规划问题，并结合序列二次规划算法求解最优化问题。仿真结果表明：采用分阶段的电磁力作用规律，优化活塞位移与速度曲线，可提高缸内气体对外做功能力与降低传热损失，使系统指示效率由41.0%增加到45.3%。同时由试验验证了所提出方案的可行性与有效性，试验中系统发电效率由28.8%提升到31.2%，系统性能明显提升。该文对此类动力装置的后续研究提供了参考。
- 发动机 /
- 优化 /
- 模型 /
- 自由活塞 /
- 运动规律 /
- 高斯伪谱法
Abstract: Abstract: The free-piston engine has an advantage of changeable piston motion trajectory because of its lack of mechanical constraint. The motion law of a four-stroke ignited free-piston engine was studied in order to improve the efficiency of the system. Based on analyzing the working principle of the system and setting boundary constraints and path constraints of the system, an optimized model of the piston motion was established. The working cycle of the free-piston engine was composed of intake, compression, combustion, expansion and exhaust phases. Based on the characteristics of separate phase of the piston motion, a trajectory optimal method called gauss pseudospectral method (GPM) was used to separate the states and control variables. In this method, the piston position, the piston velocity, the in-cylinder gas pressure and the in-cylinder gas temperature were set as the state variables and the electromagnetic forces were set as the control variables. Then the optimal problem of piston motion was discretized to nonlinear programming problem. Then the nonlinear programming problem was solved by the sequential quadratic programming method (SQP). Furthermore, the parameters of the 462 engines were taken as the computing parameters. The fuel used in the simulation was gasoline. The simulation results showed that by adjusting the separate electromagnetic force and optimizing the piston position and velocity curves, the output work increased while the heat-transfer loss reduced with the rapid piston motion. It indicated that the efficiency reached as high as 45.3% in the simulation. During the compression process, the applied time of the optimized electromagnetic force was delayed compared with the original. And the time spent in the optimized compression process was shorter than the original. During the early expansion process，the optimized amplitude of the electromagnetic force was bigger than the original, which made the in-cylinder combustion close to constant volume combustion and the gas pressure and temperature increase quickly. During the middle expansion process, the electromagnetic force was not applied, which made the piston move fast and avoid more losses of heat transfer under the condition of high temperature and high pressure. During the late expansion process, the big electromagnetic force was applied in order to meet the target expansion length. Then comparison experiments of different piston trajectories were studied under the natural aspirate. The intake air pressure was 0.1 MPa, the temperature was 303 K and the excess air coefficient was 1.05. The results were derived from repeat experiments, which validated that the optimal method was feasible and valid. The in-cylinder peak pressure had a notable increase when the electromagnetic forces were applied by separate phase. The output electrical efficiency reached 31.2% and the system performance was remarkably improved. The output electric power had a small increase, because the cycle period was extended. As a result, the proposed optimization method of the piston motion law has an important significance for the system development.
- engines /
- optimization /
- models /
- free-piston /
- motion law /
- gauss pseudospectral method

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参考文献(22)

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