This writer and many of you readers are of the need for speed crowd. Lower elapsed and transit times are good for not waiting for distance to meander by. Not that meandering isn’t a worthwhile way to travel, but for economy and the reality of life its just too much time waiting for transiting and a frustration.
David Lior, general manager of a small Israeli firm called R-Jet Engineering has a speedy more efficient and maybe quieter jet engine concept in their works. Next to rockets, with both fuel and oxidizer on board – jet is as fast as this writer is willing to go. Better engines are a very exciting prospect, especially if costs can be driven down.
Today’s modern jets with bypass turbo jets nacelles burn only half as much fuel per unit of thrust as their 1960s counterparts. These engines anchored to an airframe 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- the action. The air is guided and diffused by static blades to allow for easier ignition into the combustion chamber where it is mixed with fuel and ignited. The reaction energy arrives from rapidly expanding hot gases, which blast out of the rear of the jet and thus drives the anchored engine and the aircraft forward. The ignited gases 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. As you can tell the non moving static diffuser and the non moving static stator are roadblocks in the way of free flowing air, fuel and exhaust gases.
R-Jet’s idea is to have the air and the ignited 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 more complete and much quicker combustion. The hot gases then exit, also in a vortex, to drive the turbine. No barrier to the actions with a diffuser or a block with stator. Free moving gases with little dynamic loss.
Dr Lior, says that eliminates the need for the two sets of static blades. It also 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. 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. Bold statements, indeed.
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. A technical demonstrator isn’t going to put an engineering firm into the jet business. Radical changes in highly regulated fields like air transport where the installed base is almost uniform in design is a significant barrier to entry. R-Jet is working to get its OCN engines used first as generators to produce electricity or to power unmanned drones. With operating experience, the engines could then migrate to military aircraft and eventually airliners.
The big makers such as GE and Rolls Royce are not standing still. The visual change is the large fans in front of jet engines that are pulling air like a propeller and passing the air over the jet to muffle the exhaust blast sound. It’s effective if not as efficient as possible. Pulling some 90% of the working air over the whole engine at jet engine rotating speeds is a significant problem. Slower propellers are much more efficient. Both Rolls and GE are looking at alternatives like shorter counter rotating blades, Pratt and Whitney is considering reduction gears to slow the blade speeds down. Both offer improvements and considerable additional weight and mechanical load.
Those solutions would add significant cost to an engine and many more mechanical elements for breakdown, maintenance and inspection all built around the compress, diffuse, mix and ignite, stator straightening the flow and harvest regeneration energy in a now more than half century old, and well proven design.
It will be interesting to see if human syndromes like ‘not invented here’ and other emotional barriers will stop the major engine companies from seizing the opportunity that R-Jet has developed. If someone does, it could provide a giant leap forward for air travel and those wonderful short transit times for long distance travel.
That would be a good thing. Airlines have a hard time making money and fuel is a major expense. An ignition section revolution in jet engines could set up more decades of air travel improvements and put off the much of concern that the environmental crowd will get air travel into their sites for deep and steep fuel use restrictions. If we want to go far and fast for decades to come we might wish R-Jet and other innovators well.