Get ready, for this highly UNREALISTIC jet engine…
Boeing has received a patent, US 9068562, which combines inertial confinement fusion, fission, and a turbine that generates electricity. Currently this kind of engine is completely unrealistic given our mastery of fusion.

But perhaps in future this might be an excellent idea.

Lets imagine our standard jet engine of commercial jetliners.Somewhere in the middle of the engine lies a fusion chamber.A very strong number of lasers are focused on a single point.The hohlraum or pellet, which is a mixture of deuterium & tritium(isotopes of hydrogen) is kept at this point.When all the lasers are turned on at the same time, it creates massive pressure.This causes the hydrogen isotopes to fuse.Now according to the patent, the hot gases produced by the fusion are pushed out of the nozzle creating very high thrust.

Also, one of the by-products of the fusion reaction is lots of fast neutrons.The patent explains that there is a shield around the fusion chamber.The shield is made of fissionable material(for eg:-Uranium-235).The neutrons moving at high speed collide with this material resulting in production of high amount of heat.This heat is then transferred to drive the turbine which generates electricity.

Finally we are done with this fusion-fission jet engine thing.

imagesource:-arstechnica.com