Valveless Pulse Jet - "Jam Jar Jet" Design

"Jam Jar Jet" Design

Most of pulse jet engines use independent intake and exhaust pipe, although this is not needed. There is even simpler design where the intake and exhaust pipe (or rather just aperture) is the same. This is possible due to the oscillating behaviour of a pulse engine. One aperture can act as exhaust pipe during the high-pressure phase of the work cycle and as intake during the aspiration phase. This engine design is a bit less efficient in this primitive form due to its lack of a resonant pipe and thus a lack of reflected compressing and sucking acoustic waves. However it works fairly well with a simple instrument such as jam jar with a pierced lid and fuel inside, hence the name.

Successful versions of the jam jar jet have been run in a plastic bottle. The bottle is far more inefficient than the jam jar versions and is unable to sustain a decent jet for more than a few seconds. It is theorized that the alcohol that was used to operate the simple jet was acting as a barrier to stop the heat getting all the way through to the plastic. For the jam jar jet design to work the propellant must be vaporised to ignite which is most often done by a shaking of the jet which causes the propellant to coat the container, therefore giving the theory some validity.