Available at: https://digitalcommons.calpoly.edu/theses/3041
Date of Award
6-2025
Degree Name
MS in Mechanical Engineering
Department/Program
Mechanical Engineering
College
College of Engineering
Advisor
Patrick Lemieux
Advisor Department
Mechanical Engineering
Advisor College
College of Engineering
Abstract
The resonance igniter is a type of rocket engine ignition system that initiates spontaneous combustion without using an external ignition source. This is possible because the activation energy needed for the combustion reaction to take place is provided by the igniter as it receives propellant flow. This can simplify the igniter hardware and lends it high re-usability while enabling the use of high-efficiency propellant combinations. Its potential benefits could make it a desirable alternative to traditional approaches such as using spark igniters or hypergolic propellants. The present research strove to inaugurate the study of the resonance igniter at Cal Poly by designing, building, and testing a lab-scale prototype of the technology and attempting to achieve resonance ignition with a methane-air mixture. Within the igniter, gaseous flow travels into a sonic nozzle, creating an underexpanded jet which exits into a resonance tube closed at one end; this device is called a Hartmann-Sprenger Tube (HST). This produces a flow oscillation phenomenon that generates heat and raises the gas temperature, enabling combustion of a flammable mixture if the mixture’s autoignition temperature is reached. Ensuring choked flow in the chamber exit orifice downstream of the HST successfully stabilized the pressures within the igniter and enabled higher temperatures to be reached with increasing inlet pressure. The Hartmann-Sprenger Tube produced measured temperatures above 500°C and reached peak performance when the key test parameters NPR and S/d ratio were ∼6.2 and 2.68 respectively. Flow oscillations while at this optimal condition appeared to correspond to the Jet Regurgitant Mode, while the Jet Screech Mode produced comparatively lower temperature rise. Ultimately, the igniter was unable to produce unambiguous combustion through resonance ignition, primarily because the achieved temperatures likely failed to reach the autoignition temperature of the methane-air mixture.