A more efficient jet engine

Jet engines today use half the fuel their counterparts did 50 years ago to generate the same amount of thrust. That kind of improvement is impressive, but it’s just the starting point for the engineers at R-Jet Engineering Ltd., an Israeli company that assembled a team of ex-Soviet Union turbine experts. They have developed a new type of engine, dubbed the Orbiting Combustion Nozzle (OCN), that is said to reduce pollution, weight and the number of needed parts. Their design also costs less than conventional jet engines and has 15% better efficiency.

They explain that in conventional jet engines, air flow is changed from rotational (vortex), coming out of the compressor, to axial in the combustion chamber. Then it gets changed back to a vortex as it goes from the combustion chamber into the turbine. In the OCN, however, air flow remains a vortex from the compressor through the combustion chamber and out through the turbine.

To keep airflow rotating in the combustion chamber, the spinning turbine turns an inner casing inside the combustion chamber at the same rotational speed as the compressor at the front of the engine. The casing holds rotor blades made of Inconel 718, a metal commonly used in jet engines. The rotors cause the air to swirl, which improves its mixing with fuel. This also boosts flow propagation speeds from the 5m/sec of conventional engines to 30 m/sec, which reduces the burn time to less than 1 μsec, eliminating the possibility of NOx formation.

The moving air presents no problem with ignition because fuel is injected tangentially to the swirl flow, making fuel flow relatively slow compared to air flow.

With this approach, OCN engineers could eliminate the diffuser between the compressor and combustion chamber. In traditional jet engines, the diffuser reduces the axial velocity of the air flow to stabilize the flame in the combustion chamber. But in the OCN engine, axial flow is almost zero, so the flame is stabilized with no need for a diffuser.

Similarly, the OCN lacks the conventional turbine stator between the combustion chamber and turbine. Its purpose is to accelerate flow from the combustion chamber so that it spins the turbine fast enough for the compressor. But in the OCN approach, airflow remains fast throughout the engine.

The engine saves fuel by using a turbine with a convergent-divergent shape. It gives the engine a 93% adiabatic efficiency in small flows of about 1 kg/sec, compared with 85% in conventional turbines. And despite the spinning casing inside the combustion chamber, the use of fewer stators (compressors and turbines), as well as half the number of turbine stages of conventional turbines with the same cycle-pressure ratios, cuts manufacturing and maintenance costs.

An OCN engine would be half the size of a conventional jet with the same power, use 25% less fuel, and generate the same level of noise, according to David Lior, founder of R-Jet.