Tuesday, September 7, 2010
Jet Engine Design Advance
This looks like a project for GE who brought in the last revolution that gave us long haul jet travel. No one is excited yet because they cannot deliver an engine yet. And yes its arrival will see every aircraft been refitted as soon as possible.
The jet engine will be with us for a long time even with long distance vacuum tube trains that will connect hubs. Distribution from hubs will still need air travel at least until even denser train grids are justified.
So we have something else for the technology mavens to track.
A new way to build a greener jet engine
Jun 28th 2010
IN A world worried about global warming, improving the cleanliness and efficiency of jet engines is a priority for airlines and aircraft manufacturers. It is not just altruism: greener engines also use less fuel, so boost profit margins. Incremental improvements over the years have made a difference. Modern jets burn only half as much fuel per unit of thrust as their 1960s counterparts. But some people think it is time for a radical redesign. One of those people is David Lior, the boss of a small Israeli firm called R-Jet Engineering.
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 OCN engines could be used first as generators to produce electricity or to power an unmanned drone. With operating experience, the engines could then migrate to airliners.
The big aircraft-engine makers are exploring new ideas for jet engines. The most obvious change has been to their shape. Whereas in the 1960s, jet engines were long and slim, today they have a vast opening at the front containing a giant fan. This fan is used to blow up to 90% of the air around the outside of the compressor and combustion chamber. This air is slower-moving than that going through the jet, but its greater mass also means it provides plenty of thrust—and more efficiently too, which is why modern “high-bypass” jets burn only half as much fuel as their 1960s counterparts. They are also some 80% quieter because the mass of slower-moving air shrouds the noisy hot gases coming from the rear of the jet.
One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades. Rolls-Royce and General Electric are looking at this approach. Pratt & Whitney is exploring putting a gearbox between the fan and the turbine, because fans run more efficiently at low speeds and turbines operate better at high speeds.
However high-bypass engines are built in the future, at their core they will still have a basic jet engine. So if R-Jet’s technology can prove itself, it might provide another leap forward.