Why is cooler air mixed with combustion gases before they enter a jet engine turbine?

In a jet engine, cooler air is mixed with combustion gases before they enter the turbine primarily to reduce the overall gas temperature to a level that the turbine components can safely withstand.1

While thermodynamics dictates that higher temperatures increase engine efficiency, the materials used in turbine blades face significant structural limitations. At the extreme temperatures produced during combustion, metallic alloys lose strength and become susceptible to excessive plastic flow under the high centrifugal stresses generated by the turbine's rapid rotation.23

To manage this, air from the compressor is diverted into the combustion chamber through holes in the combustion liner to dilute the hot gases. Additionally, because modern engines often operate at temperatures exceeding 1,370° C, engineers must employ advanced cooling techniques, such as circulating cooler air through internal passages in hollow turbine blades or creating a protective cooling blanket over the blade surfaces. These measures are essential to prevent material failure and ensure the mechanical integrity of the engine.124