"Everyman's Jet Engine" - Why Valveless Pulsejets? No ignition system needed after startup Once our pulsejet is started and running, there is no need for electric ignition. Many people assume that this is because of the red hot shell of the combustion chamber, but this has been proven false. The real source of ignition in a running engine is the fact that the combustion chamber pulls hot gas back in from the tailpipe during the final phase of the engine cycle. There are sufficient free radicals in this gas (as well as explosion gas residue in the chamber) to cause ignition of the next air-fuel charge that is breathed in, once the pressure comes back up to a certain threshold level. This completely relieves us of the need to carry the weight of an ignition system and battery in the vehicle.