ATREX

The ATREX engine developed in Japan is an experimental precooled jet engine that works as a turbojet at low speeds and a ramjet up to mach 6.0.

It uses liquid hydrogen fuel in a fairly exotic single-fan arrangement. The liquid hydrogen fuel is pumped through a heat exchanger in the air-intake, simultaneously heating the liquid hydrogen, and cooling the incoming air. This cooling of the incoming air is critical in achieving a reasonable efficiency. The hydrogen then continues through a second heat exchanger positions after the combustion section, where the hot exhaust is used to further heat the hydrogen, turning it in a very high pressure gas. This gas is then passed through the tips of the fan providing driving power to the fan at sub-sonic speeds. After mixing with the air, it's then combusted in the combustion chamber.

Intended applications for the engine are for launching vehicles in to space.