Experimental investigation of the effects of different internal surface features on additive-manufactured resonant igniters performance

Resonant igniters are attractive for liquid rocket engines using non-hypergolic green propellants (envisaged to replace hydrazine and its compounds) especially when multiple restarts are required. They exploit the interaction of an under-expanded jet flow with a downstream cavity to obtain a significant temperature rise. Compared to other ignition systems, they do not require any external energy source or the use of any auxiliary fluid or catalyst, and result to be low-weight, reliable, and simple. Nevertheless, a fine-tuning of many design parameters is required to grant proper igniter performance. In order to assess the potentiality of these igniters, an experimental campaign has been carried out at Politecnico di Torino. Additive manufacturing was used to produce complex internal geometry of the resonance cavity to investigate the effects of different internal surface features on igniter performance. Inconel 625 was used as a material. Cold tests have been carried out using compressed air, with a Nozzle Pressure Ratio ranging from 3 to 9 and a normalized distance between the cavity and nozzle exit in the range from 2 to 4. Complex internal surface features of the walls inside the cavity appear to improve the operative range of the Nozzle Pressure Ratio where high temperatures are obtained, without significantly affecting the temperature increase due to resonance. A maximum temperature of 952 K was measured.