So Gambit can you please elaborate in WVR scenario how this blue flame may effect on situation is this vulnerable for aircraft.
A blue exhaust came from a higher combustion temperature, which translate to a higher infrared signature. Am sure you can take it from here.
2ndly is this due to the mixture or composition of fuel or the engine design.
From both...
First...You should understand that a higher combustion temperature does not mean the engine is of a 'poor' design. There are many factors working together to qualify any engine as 'poor' or 'superior' when compares against each other.
Second...As a preemptive measure in case anyone tries to tell you that if China is able to design an airliner engine, China can design a military class jet engine. That is completely wrong.
In the above, you can see the great differences between an airliner jet engine (middle) and a military class jet engine (bottom). The top illustration is to show what they have in common: a combustion core.
The airliner jet engine is called a 'high bypass turbofan' type. The majority of thrust comes from the (green) fan assembly. It is this air mass and flow that we call 'bypass' air.
The military class jet engine is also a turbofan design but the bypass air is so low that the engine design is nearly a 'turbojet' type. The bulk of thrust comes from exhaust.
In terms of performance, if you want high thrust and acceleration, you want the turbojet design. If you want fuel economy and durability, very vital to the financial bottom line of an airline company, then you want the high bypass turbofan design. In the middle lies the low bypass turbofan design, which is in the bulk of jet fighters out there.
What distinguish one low bypass engine from another ? Efficiency. As in how effective does the engine burns fuel. For example...An engine that can regulate fuel flow and atomization in tenths or even hundredths of percentage points is more efficient than an engine that regulate fuel flow and atomization in single digit percentage points. There are many other factors involved that are beyond the scope of this discussion. I just want you to know that a military class jet engine is a wholly different beast than an airliner jet engine.
So while a higher combustion temperature does not mean an inferior engine design, it does mean materials will break down sooner than when under lower temperature. This is where Russia and China are behind the US and other Western companies: materials science, specifically engine blade composites. Engine hours are closely monitored and a fighter will be taken offline for engine change if the engine approaches the limit of those operating hours. In this case, an engine with a lower combustion temperature with high durability blade composites will have longer engine operating hours, therefore, can stay on the 'combat ready' status longer.
Am sure you can see where this is heading.
