Design and experimental study of an ultrasonic assisted igniter for enclosed environments

Ultrasound technology, as a versatile activation method, offers notable advantages in accelerating oxidative combustion, improving flow fields, and reducing emissions. Yet ultrasonic-assisted combustion currently faces two major limitations: first, the understanding of ultrasonic ignition and combustion mechanisms remains incomplete; second, existing applications predominantly rely on generic piezoelectric transducers, which are not tailored to the constrained environments of combustion chambers, where spatial limitations and fuel properties pose specific challenges, resulting in a lack of specialized transducers. This study integrated theoretical modeling with experimental validation to systematically design and optimize ultrasonic-assisted combustion igniters. A 35-kHz high-efficiency device was designed, and its impedance characteristics and dynamic resistance were optimized through an iterative optimization strategy based on impedance feedback. The piezoelectric stack topology was upgraded from a dual-plate configuration to a four-plate configuration, increasing the power-handling capacity by a factor of 3.7 relative to the original system. A focusing amplitude-rod acoustic architecture was introduced, markedly enhancing the flame development rate. Finite element simulations validated that the theoretical target frequency aligned with the longitudinal resonant mode, with an error of 0.03%. Experiments were conducted in a rarefied hydrogen environment, using a hydrogen-air mixture as the fuel on a constant-volume combustion bomb platform. Three ultrasonic-assisted combustion igniters exhibited different influences on flame development, but all promoted flame propagation, with more pronounced effects observed near the lean-burn limit. The results provide theoretical support and optimization strategies for practical applications of ultrasonic-assisted combustion technology.