Enhanced thermodynamic performance of a modified α type Stirling engine with fine-tuned piston trajectories controlled via staircase decomposed target signals

Actively controlling the thermodynamic process is an effective tool to achieve superior heat engine performances. However, conventional linkage type engines have limited abilities in actively controlling of the piston trajectories. Facing this challenge, this paper proposed new α type Stirling engine with actively tunable thermodynamic cycles. The primary innovation of this research is that the traditional fixed displacement coupler links of the engine are replaced by two micro power screws, allowing for the cycle-to-cycle active control of pistons’ trajectories. Mathematical models regarding the new engine dynamics are established, with the new process trajectory planning models derived. A new α-type Stirling engine testbed is assembled in lab, which is capable of monitoring the piston trajectories, the coupler length, and various thermal dynamic parameters to allow for the validation of the proposed engine architecture. A new cycle-wise reference tracking algorithm, contrast to the traditional time step tracking one, is presented based on finite step response functions (staircase decomposition). Results have shown that the proposed system can fine-tune the pressure-volume trajectories within a cycle. Consequently, the tuned boundary work can be increased by 17%, 22%, or 42% from the baseline counterpart at cycle times of 3.2s, 6.4s, or 9.6s, respectively.