Analysis and control of a spark ignition free-piston engine generator

Abstract

In this research, the performance analysis and control strategy of a spark-ignited free-piston engine generator were presented. A literature review of the free-piston engine fundamental information and the recent research development on the free-piston engine generator (FPEG) was provided, mainly focussing on previous work on numerical modelling, prototype design as well as the control strategy. The design and simulation of a dual-piston spark-ignited FPEG suitable for operation using either a two-stroke or four-stroke thermodynamic cycle were presented. Model validation and the general engine performance of the system were discussed. For the first time, this research demonstrated the potential advantages and disadvantages of the FPEG on using different thermodynamic gas-exchange cycles. A fast response real time model of the FPEG was designed and validated. The simplicity and flexibility of the proposed model make it feasible to be implemented and coupled with real-time hardware in the loop control system development. In addition, since it revealed how an FPEG operates according to a resonant principle, the model is useful for parameter selection in the design process. For the first time, cascade control was proposed and investigated for the piston stable operation control, using both the measured piston top dead centre of the previous stroke and the measured piston velocity at the current stroke as feedbacks, with the injected fuel mass as the control variable. The system performance was improved by implementing the cascade control compared with single loop control in terms of the controller response time, peak error and settling time.