Design and control of a controlled trajectory rapid compression and expansion machine

This paper presents the design of a controlled trajectory rapid compression and expansion machine (CTRCEM) that offers the unique capability of real-time piston trajectory control. While in a conventional rapid compression machine/rapid compression and expansion machine (RCEM), changing the operating parameters such as compression ratio and compression time requires mechanical alteration of the hardware, the same can be achieved in the CT-RCEM merely by changing the reference trajectory fed electronically to the controller. With this capability, a CT-RCEM offers higher operational flexibility, wider range of operation, and better repeatability compared to the current state-of-the-art RCEM. More interestingly, a CT-RCEM is naturally suited to investigate the coupling between the piston trajectory and the combustion kinetics-a phenomenon that is extremely difficult to investigate using conventional combustion research facilities. However, high-speed operation and high-force requirement for piston motion present a major challenge for design and control of a suitable actuation system that can provide precise motion control. For the design of the CT-RCEM, first, a dynamic model is developed to understand the impact of various design parameters on the system performance and to identify suitable control strategy for the actuation system. The design parameters in the dynamic model and the controller are tuned in-tandem using simulation studies to obtain the system specifications,which are subsequently translated into amechanical design. Experimental results obtained after commissioning of the designed CT-RCEM demonstrate that the desired functionality of real-time piston trajectory control has been achieved.