Editing Ramjet (section)

===Precooled engines===
{{Main|Precooled jet engine}}
A variant of the ramjet is the 'combined cycle' engine, intended to overcome the ramjet's limitations. One example of this is the [[Reaction Engines SABRE|SABRE]] engine, which uses a precooler, behind which is the ramjet and turbine machinery.

The [[ATREX]] engine developed in Japan is an experimental implementation of this concept. It uses [[liquid hydrogen]] fuel in a single-fan arrangement. The liquid fuel is pumped through a [[heat exchanger]] in the air intake, simultaneously heating the fuel and cooling the incoming air. This cooling is critical to efficient operation. The hydrogen then continues through a second heat exchanger position after the combustion section, where the hot exhaust is used to further heat the hydrogen, turning it into a high pressure gas. This gas is then passed through the tips of the fan to provide driving power to the fan at subsonic speeds. After mixing with the air, it is burned in the combustion chamber.

The [[Reaction Engines Scimitar]] was proposed for the [[LAPCAT]] [[hypersonic]] airliner, and the [[Reaction Engines SABRE]] for the [[Reaction Engines Skylon]] spaceplane.