An engine being developed by Reaction Engines which operates in two modes - air-breathing up to Mach 5, and rocket mode to orbit. The key to making it work is pre-cooling the air before it's ingested and burned with liquid hydrogen. This advanced heat exchanger is the focus of their activities, and all tests to date have shown that it works, and the problematic frost caused by the moisture in the air has also been overcome. Note - this engine is not a scramjet, and does not have anything in common with them.
The engine seems to resemble the engine used for the SR-71 blackbird, with nosecones forcing certain airmovement, and conversion of the engine into a different type of engine. It is different though by the curvature and the pre-cooling of the air.