Design and Test of an Augmented Spark Igniter With Interchangeable Flow Control Orifices

An ultra-lean, modular augmented spark igniter was developed and validated for rocket engine test stand applications requiring extreme operational flexibility. The design employed interchangeable choked orifices to achieve independent control of the mass ratio and igniter chamber pressure while sharing gaseous oxygen and methane propellant supplies with the main chamber. Three experimental campaigns validated igniter performance: ten consecutive atmospheric discharge tests established repeatability, ten consecutive tests demonstrated fuel-rich main chamber ignition capability, and systematic variation from mass ratio 11.24 to 30.74 and igniter chamber pressure 627 to 2034 kPa characterized operational limits. Combustion efficiency correlated strongly with chamber pressure (R^2 = 0.9371), ranging from 30% at 627 kPa to 95% at 2034 kPa, with the relationship arising from propellant stay time effects quantified through characteristic chamber length. Higher pressure increases gas density and extends propellant stay time for fixed chamber geometry, enabling more complete combustion. The combustion efficiency and normalized characteristic length correlation (R^2 = 0.9647) provide insight into igniter performance and design guidance for specific pressure regimes. The plasma-assisted configuration with momentum controlled flame location enabled reliable ultra-lean operation while igniting fuel-rich main chamber propellants. A low-cost commercial off-the-shelf approach provided flexible ignition capability for subscale rocket engine testing requiring variable and extreme operating conditions across wide mass ratio and pressure ranges.