It has been couple of decades since India embarked on a project to build a modern low bypass turbo fan jet engine, compatible with the Light Combat Aircraft Tejas at the Gas Turbine Establishment GTRE of the Defence Research & Development Organization DRDO.
The engine under development, named Kaveri, has faced multiple hurdles both technological and bureaucratic over the years. Nonetheless, the Defence Metallurgical Research Lab (DMRL), a lab under DRDO has produced a new proven thermal barrier coating material, that has a maximum surface temperature capability of 1200°C.
This development, will provide a useful baseline for the progression of jet engine technology in India.
A jet engine produces thrust not unlike an internal combustion engine. Air is drawn in and compressed by the compressor section. Fuel is then mixed with this compressed air and ignited producing a great amount of gases which are then used to rotate a turbine to extract work.
The turbine and the compressor are connected via a common shaft such that fuel ignition is utilized to drive the compressor and continue engine operation. Military as well as modern civilian use place a great premium on weight, specific fuel consumption, maximum thrust as well as low maintenance requirements and long life of components.
One of the primary limiting factors that limit thrust and fuel consumption in a jet engine is the temperature of exhaust gases. Titanium, a metal widely used in aerospace applications, readily undergoes oxidation below temperatures of exhaust gases. Hence, Nickel alloys are used for ‘hot section’ components of the jet engine.
Today, even the high pressure compressor turbine blades of the Kaveri engine utilise indigenous Ni alloy SUPERNI718A due to the high temperatures. Ni-alloys by themselves however are not robust enough to prevent heat and aero-mechanical stress related deterioration of turbine blades.
Extended exposure to high temperature and mechanical stress results in creep-fatigue that causes failure of turbine blades. Reducing thermal exposure of the turbines therefore is vital to extend their life.
Layers of oxidised material called TBCs are applied to high temperature sections of the engine such as turbine blades and vanes for this purpose. Air cooling vents are also used to provide a barrier on top of the blades and vanes to lower heat transfer.