From this weeks Economist

Jet engines rely on Isaac Newton’s third law of motion: for every action there is an equal and opposite reaction. When a jet is running, a compressor at the front draws in air and compresses it (see illustration). This air is guided and diffused by static blades to allow for easier ignition when it is mixed with fuel and ignited in a combustion chamber. The reaction comes in the form of rapidly expanding hot gases, which blast out of the rear of the jet and thus drive the aircraft forward. As they do so, they pass through another set of static blades which direct and accelerate the hot gases to turn a turbine. The turbine is connected by a shaft to the compressor at the front, thus turning it and keeping the whole process running.

The approach taken by R-Jet involves having the air and hot gases in the combustor rotate with the compressor and turbine. To achieve this, the company uses what it calls an orbiting combustion nozzle (OCN), which turns with the compressor to inject the air into the combustion chamber as a vortex. The vortex is maintained by blades that rotate on the inner casing of the combustor. This swirling action helps mix the air and fuel for a more complete and much quicker combustion. The hot gases then exit, also in a vortex, to drive the turbine.

This, says Dr Lior, eliminates the need for the two sets of static blades. That means an OCN engine can be built more cheaply with fewer components. It would also need to be only half the size of a conventional jet of similar power, says Dr Lior. The engine would use at least 25% less fuel and, he claims, its emissions of carbon dioxide and nitrogen oxide would be cut by three-quarters because of its unique ignition properties.

So why are airlines not beating their way to R-Jet’s door? The company, founded by a group of Israeli military officials and jet-turbine experts from the former Soviet Union, has built a technology demonstrator but needs a bigger partner to take the concept further. As with any radical change to an existing technology, especially a jet engine, a large installed base of expertise together with lots of regulation mean it can be hard for a newcomer to make headway. To ease its entry into the market, R-Jet reckons that OCN engines could be used first as generators to produce electricity, or to power unmanned drone aircraft. Having established a track record for themselves in this way, the engines could then migrate to their intended use on airliners.