Compressed-air vehicles have the advantages of zero pollution and low cost. A compressed-air engine test bench is established in this study. The effects of rotational speed, torque, and regulated pressure on the power performance, economy, and energy conversion efficiency of the pneumatic motor are investigated. The differences in power output, compressed-air consumption rate, and energy conversion efficiency between forward and reverse rotation of the pneumatic motor are compared and analyzed. To effectively investigate the performance of a compressed-air vehicle under various road conditions, this study compares and analyzes the power performance, economy, and energy conversion efficiency of pneumatic motors under different road conditions. Experimental results show that the power output and energy conversion efficiency of the pneumatic motor in reverse rotation are less than those in forward rotation, indicating that the pneumatic motor has better power performance and higher efficiency with forward rotation than reverse rotation. The compressed-air consumption rate of the pneumatic motor with reverse rotation is higher than that with forward rotation, indicating that the pneumatic motor with forward rotation has better economic performance than with reverse rotation. The maximum power output and energy conversion efficiency of the pneumatic motor are about 1220 W and 13.23%, respectively.

The structural design and operating strategy of a free piston expander–linear generator (FPE–LG) has a major impact on performance. In this paper, the simulation model of single–piston FPE–LG was built and verified by combining the structural parameters of the existing test rig with a set of kinetic and thermodynamic equations. On this basis, the influence of the design and operating parameters of the device on the performance was studied, while keeping other parameters fixed. Then, a sensitivity analysis of power output and operating frequency was carried out. The results show that within a certain range of external load and intake beginning position, increasing the diameter of the intake and exhaust pipes, or reducing the piston rod diameter can improve the power output. Within a certain range of frictional coefficient and intake time, increasing the cylinder diameter and intake pressure, or reducing the piston assembly mass and back electromotive force (EMF) constant can increase the operating frequency. Both the power output and the operating frequency are most sensitive to the cylinder diameter among the design parameters. Among the operating parameters, power output is the most sensitive to intake pressure, and operating frequency is the most sensitive to intake beginning position. The optimization of structural design and operation strategy in expander provides important guiding significance for ORC waste heat recovery system.

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