Working characteristics of two types of compressed air engine

To avoid environment pollution caused by internal combustion engine vehicles, compressed air engines (CAEs) have attracted much attention over the past decade. Two kinds of compressed air engines, single cylinder piston-type CAE (SCAE) and double crank link CAE (DCAE), have been investigated. However, SCAEs have low energy efficiency and output power; particularly, when rotational speed is high. To solve these shortcomings, the DCAE is proposed, which can obtain higher output power at higher rotational speeds. Using co-simulation technology, the average output power, energy efficiency, and cylinder pressure of the two kinds of CAEs were obtained. The average output power and efficiency characteristics of the SCAE were obtained by simulation and experiment; the simulation results were consistent with the experimental results, which verified that the united simulation model is accurate and effective. The results show that the pressure inside the DCAE cylinder is barely influenced by the rotational speed, and the output torque remains generally stable with an increase in the rotational speed. The average energy efficiency of both kinds of CAE declines with an increase in the rotational speed when the supply pressure is set at 2 MPa. The air power efficiency of the DCAE is about 1.86-2.86 times that of the SCAE. When the rotational speed is 800 rpm, the air power efficiency of the DCAE is 2.86 times than that of the SCAE. It is clear that the DCAE can improve the CAE performance under high rotational speeds.