737NG CFM engine temperature drop
 

Does anyone know how much the temperature drops in the inlet of a CFM or similar jet engine? I work in China and they insist that engine anti ice isn’t mandatory at 10 degrees C, I know it’s unbelievable but I’d like to give them some “evidence” thanks

Who is "they" ?

Our Chinese line training instructors。。。

Hardly wise trying to point score with them...

Considerations for flight crews

Have fun with your "instructors".

are we talking in the air or on the ground?

on the ground the air is sucked, in the air it's rammed. The 10C limit is close enough to be safe. Play with it and you take your chances with engine icing while in visible precip (snow, ice, fog, rain).

I suppose that if you define all the condtitions somebody could make a calculation of temp along the surfaces in an inlet and the fan blades

Much less harm is done by having TAI on at 11 degrees than off at 9 degrees. YMMV.

FCOM is very clear. And if they insist... well, you know why you're getting paid all that money.

I did ice up like hell with TAT +11°.
Cross-checked with the other TAT sensor.
With CFM 56. In China.

My understanding is that the requirement to turn on cowl (inlet lip) anti-ice, which also raises the idle setting, at temperatures above 0C TAT has more to do with the indicated TAT range at which you can have supercooled water droplets due to atmospheric convective or precipitation action and the difference between OAT and TAT rather than any temperature drop the air experiences passing through the inlet. As said above, in high speed flight and in low speed low power flight the air temperature rises slightly as it slows down in the inlet.

Again the original OP never defined the operating conditions regarding flight e.g. are we ramming air (in-flight) or sucking air (on taxi out or in.) and where is the ice assumed to be forming (on the inlet surfaces or on the engine surfaces). There are different levels of protection involved.

Exactly - the risk of inlet icing is dependent on not only the air temperature, but on the airspeed and the engine power setting. At low speed, the air going in the inlet speeds up and cools, while at higher airspeeds the air slows down and warms passing through the inlet, with the amount of that heating or cooling related to the engine power setting. +10 deg. C protects for most foreseeable conditions where water/supercooled droplets could cause icing, without requiring the pilots to look up on a complex chart to see if there is a risk of icing.

In flight, (at least on Boeing), selecting engine anti-ice increases the idle speed to insure the bleed air used for anti-ice is warm enough, with enough pressure to do the anti-ice job.

Just to add, after reviewing the early historical records of engine related icing, the safety gurus in the industry took note of the variances between manufacturers, AC and engines regarding ambient temperature "limits" in precips (we hadn't known about super-cooled at that early time). Indeed these early limits did vary by 5 degree C. The decision was made to harmonize at +10C to avoid confusing pilots transferring between products. This decision seems to have worked out well where it has been followed and is embraced uniformly

Simply show them FCOM 1. It clearly says when TAI is required.