Care to show me where I mentioned lower exhaust temps, George? You didn't . . . I did.

Oh right, you can't. I didn't mention it.

The AVERAGE temp of the exhaust for a high bypass turbofan is lower than a comparable thrust turbojet, but do you know why?

Bet you don't.

Ever look at the temp profile behind an operating high bypass turbofan? Bet not.

I think a horny baboon may edge you out on the aerospace engineering front, George.

The indirect effects of water vapour (contrails and contrail-cirrus) and particles from aircraft may play a major role in the climate impact of air traffic. The contrail formation is affected by the engine propulsion efficiency, which grows with decreasing exhaust gas temperature. An engine performing with a higher overall propulsion efficiency causes plume conditions which during mixing reach a higher relative humidity for the same ambient temperature, thus causing contrails also at a higher ambient temperature. This paper is aimed at finding technical solutions for the aircraft engines that temporarily decrease the propulsion efficiency, and thereby may alleviate the formation of contrails.



Now, what is the average exhaust plume temp of a high bypass turbofan versus the exhaust plume temp of a comparable thrust turbojet?

You have the answer in your hand and did all along, but you either refuse to or are incapable of putting the pieces together.

Don't know yet but I will try to find out . . .



Think logically, George.

If you surround a high temp core of gas with a very large volume of much lower temperature gas, what happens to the AVERAGE temperature of that gas.

Simple logic and everyday experience will tell you the answer.

Thanks for the info . . . makes sense.



That doesn't answer the question, George.

What makes sense? Explain so we know you have absorbed the lesson.

The lower temperature of the large volume of air would naturally lower the temperature of the smaller volume of air . . as long as they are in contact with each other (mixed). I would suspect the new temperature would be a rough average of the two volumes of air.



And the exhaust stream temp has what effect on contrail formation?


The lower the stream temp the quicker the vapor probably forms nuclei and or ice crystals which result in more persistent trails and eventually cirrus clouds in the right conditions. Research suggests the smaller the nuclei the greater the albedo effect of the cloud formed by them . . . thus higher rates of climate cooling.