Development Approach of a Spark-Ignited Free-Piston Engine Generator

The free-piston engine generator (FPEG) is a novel type of energy conversion device; it integrates a two stroke combustion engine and a linear electric machine into a single unit. As an alternative to conventional engines, the FPEG is a promising power generation system due to its simplicity and high thermal efficiency and has attracted considerable research interests recently. This paper presents the development for a spark-ignited free-piston engine generator prototype, and the design of major sub-systems is introduced. The electrical linear machine is operated as a motor to start the engine and switched to a generator after successful ignition. Ignition is one of the most crucial problems for the generating process, thus a unique control sub-system to generate ignition signals at the correct ignition timing based on the piston position was completed. Then experiments of the starting process were carried out with the prototype. The results indicate that with a fixed motor force of 110N, the maximum in-cylinder gas pressure can reach 12 bar and the compression ratio can reach 8:1. Moreover, the experiment results show a good agreement with the simulation prediction. According to the performance of the starting process, the development of the prototype is acceptable and further research on the generating process will be undertaken soon.