Coil-On-Plug Igniter for Reliable Engine Starts - Tech Briefs

Johnson Space Center, Houston, TX

Innovators at NASA Johnson Space Center have developed a coil-on-plug ignition system for integrated liquid oxygen (LOX)/liquid methane (LCH4) thermal-vacuum environment propulsion systems operating in a thermal vacuum environment. The innovation will help quell corona discharge issues and reduce overall mass.

Spark-ignition devices have proven to be a high-reliability option for LOX/LCH4 ignition during development of the Integrated Cryogenic Propulsion Test Article (ICPTA) main and reaction control engines (RCEs); however, issues including spark plug durability (ceramic cracking) and corona discharge during simulated altitude testing have been observed, contributing to degraded spark output and no-light engine-start conditions.

Innovators discovered that ignition system reliability could be improved and weight reduced by eliminating the traditional coil and spark plug wire. To achieve this result, engineers made the innovation by modifying an automotive coil-on-plug igniter to provide new high sparking energies at the point of combustion using low supply voltages.

The coil was modified by vacuum-potting it into a threaded interface that mounts into existing spark plug ports on the ICPTA main engine and the RCEs. Engineers fabricated custom electrode tips that were thread-mounted into the potted coil body. Epoxy insulation was chosen with high dielectric strength to maintain insulation between the electrode and threaded adapter.

Vacuum potting successfully prevented pressure or vacuum leakage into the coil body and maintained spark energy and location at the electrode tip. Successful hot-fire ignition was observed at sea-level, altitude, and thermal-vacuum for both ICPTA RCE and main engine igniters down to 10-3 torr, which approaches the vacuum of cislunar space.

The coil-on-plug configuration eliminates the bulky standalone coil-pack and conventional high-voltage spark plug cable by combining the coil and the spark plug into a single component. The test campaign successfully proved that coil-on-plug technology can enable integrated LOX/methane propulsion systems in future spacecraft.

NASA is actively seeking licensees to commercialize this technology. Please contact NASA’s Licensing Concierge at This email address is being protected from spambots. You need JavaScript enabled to view it. or call at 202-358-7432 to initiate licensing discussions. For more information, visit here .

This article first appeared in the December, 2023 issue of Tech Briefs Magazine.