Experimental and numerical analysis of stable performance of dual cylinder linear range extender with auxiliary spring

The free-piston linear range extender (LRE) is a new power system that converts chemical energy directly into electrical energy, providing an efficient and clean energy conversion solution for hybrid power systems. Here, we innovatively propose a spring-assisted LRE (SLRE) system, which introduces a spring mechanism into the configuration of the dual-cylinder reciprocating rebound for the first time. It significantly improves the dynamics of the conventional LRE system, and its effectiveness is experimentally verified. The system achieves dynamic regulation of the piston trajectory through a phase-matching mechanism between the elastic potential energy and the combustion kinetic energy, resulting in significant stability and output performance optimization. The experimental results show that the cylinder pressure fluctuation of the SLRE system is reduced by 38.69 %, the dead center concentration is increased by 30 %, the indicated work fluctuation is reduced by 49.85 %, and the operating frequency is improved by 0.99 Hz compared with the conventional LRE system. Further, the matching of spring stiffness and compression ratio is a key factor for system stability, which provides a theoretical framework for multi-parameter co-optimization and an innovative solution for designing high-performance and high-stability LRE systems.