In liquid propellant rocket engines, spark igniters are often used indirectly to light preburners, gas generators, and main chambers [1]. Attraction for spark igniters is strongly influenced by their ability for repeatable engine starts and high reliability. In the case of spark igniters, however, ignition is reliant upon an ignitable mixture passing near the spark tip very early in the engine start transient, prior to pressure quenching of the spark. While direct ignition of rocket engine combustion chambers is possible and has been successfully implemented in engines such as RL-10, the development time can be significant since ignition requires precise and repeatable control of the propellant mixture ratio within the very small volume and short duration of the spark plasma. Generally, the preferred method of implementing spark igniters within rocket engines - especially larger engines, is to design a smaller "augmented spark igniter" pre-chamber in which propellant injection and mixture ratio near the spark plasma can be controlled independent of the engine injector. The resultant combustion products within the small pre-chamber are directed into the larger engine chamber via a torch tube. An augmented spark igniter is advantageous because the output torch flame that is much larger and more energetic than a discrete train of small spark plasmas.
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