Is Wonder Woman's invisible jet a conventional aircraft (based on aircraft from her timeline and cloaked)? If not, what kind of power plant and fuel does it utilize?
The early version(s) of the Invisible Jet never indicated what the plane used for fuel, what kind of power source it utilized, nor fully defined what it was capable of doing. Marston was not a aeronautic type and thus used it as a plot device to allow Wonder Woman to fly, since in the early writings she could not truly fly.
Post-Crisis Wonder Woman COULD fly and thus had no need of the Invisible Jet, as such. When the Post-Crisis rewrite was done, the Invisible Jet became a piece of alien technology/sentient life form.
To ret-con this for Wonder Woman continuity, the device time travels back to the past so that Wonder Woman's mother Hippolyta who was now the Golden Age Wonder Woman, uses the Lansinarian device as a World War II era plane.
The Lansinarian device did not appear to utilize a power source recognizable to human science and acted pretty much as any good plot device should, without explanation, until it died.
In short, her first plane was a gift from the Goddess Diane to her Amazons. It initially appeared in the form of a propellor plane but then morphed into a jet plane (strongly resembling a Gloster Javelin) without any further explanation.
In a later comic we see another plotline (that contradicts the earlier one) where the plane morphs from a Pegasus into a much snappier jet plane.
The first version simply appears to run on magic. It's a gift from the gods and apparently that's all the explanation needed.
The most recent version of the plane is actually a crystalline entity that was originally capable of changing into a variety of shapes including a plane but also a bike, a train and a person called WonderDome. The fuel for this later version appears to be "Graviton Particles" which it collects from the atmosphere.
Like most comic-book questions, there's far too many inconsistencies to actually come up with a single conclusive answer. For example, why does the 1960 concept art have "external fuel cells" on it?
And why does she think there might be a "Fuel Leak"?