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Lighting a Regeneratively-Cooled Liquid Bipropellant Rocket Engine
Space Enterprise at Berkeley | September 2023 - November 2024
Space Enterprise at Berkeley | September 2023 - November 2024
Project Overview
Project Overview
As a part of SEB's goal to reach space with a liquid bipropellant rocket, our team designed a new regeneratively-cooled rocket engine, HeavyBulb, with a predicted thrust of over 3 times that of our previous ablative engine, and switched propellants to nitrous oxide and isopropanol (IPA). With a scaled-up engine and new propellant feed system, there comes a need for a more energetic ignitor.
As with any other liquid bipropellant system, the ignitor must impart sufficient heat flux into the stream of mixed propellants coming from the injector to begin a combustion reaction in the chamber of the engine. Ignition must occur within small window; if propellants are not lit at the right time, the high flow velocities and pressures inside the engine could result in a cold flow or hard start from chamber overpressure, both coming with their respective catastrophic consequences.
Although SEB had successfully ignited a liquid oxygen/propane ablative engine in the past, our team had no experience with igniting nitrous and IPA. Nitrous has been known to be difficult to ignite, and with the higher flow rates in our new regen engine, ignition proved to be a much more difficult task than expected.
Design Overview
Design Overview
To reduce design and integration complexity, solid rocket motor propellant was fixtured up the throat of the engine to ignite propellants.
The shaft of the ignitor is designed to hold 38 mm solid rocket propellant, and holes were placed at the base of the shaft to allow for e-match wires to pass through and connect to the wire for the pad key box. A mounting plate is fixtured to the manifold of the engine, and an outer plate is bolted to the mounting plate using nylon shear pins at the widest points of the two outer plates. The shaft is then fixtured to the outer plate, and during a burn, the nylon shear pins should shear at the head, causing the shaft and outer plate to fly off, leaving the mounting plate still attached to the engine.
The final assembly of the ignitor included six e-matches wired in series to light the exposed solid propellant retained in the shaft. The e-matches were placed in two radial patterns of three e-matches on the outside of the exposed propellant.
Testing
Testing
Testing of the ignitor was extensive and essential to ensuring the performance of the ignitor during a static fire. Both DMS (single-use) and RMS (reusable) solid motors of various sizes were tested, in addition to testing different types of commercial-off-the-shelf (COTS) propellants.
In the final ignitor, a long stick of 38mm Propellant X was used, as it burned for sufficiently long at higher temperatures compared to other COTS propellants, and the flame produced by the solid propellant was large enough that we believed it would not get extinguished by the flow of liquid propellants coming from the injector.
The ignitor was also integrated on to the engine for cold flows to determine how the mount would perform during a hotfire. Because the thrust produced by a cold flow is significantly less than that of a real static fire, we wanted to discern whether the ignitor fixture would blow off after being lit based on the thrust produced during a cold flow. If the ignitor fixture blew off, it would indicate that the ignitor would not be held inside the engine long enough to light propellants.
Ignitor set off via six e-matches, flame becomes visible from outside the chamber, command sent to begin flow of propellants
Flow begins and thrust from the engine shoots the ignitor fixture out of the chamber
Flow expands to nominal state, burn continues
Photos: Ian Leifer
Remnants of the Ignitor Assembly Post-Hotfire:
Remnants of the Ignitor Assembly Post-Hotfire:
Heavybulb Hotfire 2.movVideo: Ian Leifer
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