Warming engines

[Toga]

In the A320 we get a ecam message if we press the TO config before the engines have 'warmed' up sufficiently - a consideration for OET. On the 744 are you just required to remember or does it warn you beforehand if it hasn't been > 3 mins.

T 

[skelsey]

Oil temperature is not monitored by the takeoff configuration warning in the B744, no. The requirements (for RR engines -- don't know about the others) are that the oil temperature must be above -10C before advancing the thrust lever from idle and above the lower amber band for takeoff.

3 minutes warm-up unless the engines have been shut down for more than 1.5 hours in which case you need 5 minutes (start the stopwatch!).

All are memory items AFAIK.

[Will]

Memory items, egads... I'm getting too old for more memory items, lol.

I obviously don't fly the real 747, so I add the memory items to my flow/checklist PDF, which is explained in far too much detail here:


http://aerowinx.com/board/index.php?topic=3578.0

[emerydc8]

The 767-300 has the slightly more powerful GE CF6-80C2B6F engines, but I think our 744s use the same guidlines: If the engines have been shut down for six hours or less, you only need a 4 minute warmup prior to takeoff. If they have been shut down for more than six hours, you need a minimum of 10 minutes, but 15 is preferred. No EICAS indication on this.

[Jeroen D]

I was just wondering, what is that will actually wear/tear on your typical jet engine when you don't warm it up properly.

Being a former Marine Engineer I have had a lot of experience and was even involved in some testing on large marine diesels.

There are two aspects to starting a large diesel and increasing the power to quickly:
- Thermal Shock
- Wear and tear due to poor lubrication

Thermal shock would usually become apparent on cracked cilinder heads and or cilinder liners. On very large two stroke engine it might take as much as a few hours running on what is known manoeuvring full speed to full speed. Over a period of 1-2 hours the engine RPMs are slowly increased. Do it too quickly and you are guaranteed cracks in the cilinder liners.

Wear and tear due to poor lubrication is mainly on the piston rings and cilinder liners. If the liner is still to cold, the lub oil won't spread properly. (this is one of the main reason you are being told not to idle your car engine, but drive away carefully immediately and keep the revs low for the first ten minutes or so. Car's petrol and certainly modern diesel engine don't warm up during idle much. You have to get them to produce some power.

Although the internet is full of stories about bearings wear and tear due to low temp oil, in practice on car engines it doesn't appear to big a problem.

I have sailed on Anchor Handling Tugs that also came equipped with two huge fire monitors. They could throw up a lot of water all the way up to 100-125 meters to reach an oil platform. Powered by gas turbines, i.e. jet engines. Two 4.500 HP units or so.  I seem to recall we did keep the lub oil heated, but nothing else. Started and immediately to full power. Same is true for power generation back up sets, these days huge gas turbines. Of course, wear and tear might not be a factor as such, or rather not that relevant for these applications. It's not about avoiding wear and tear. It's about going to 100% power as quickly as possible occosionally

So if you don't properly warm up your jet engines, what is that will actually wear?

[emerydc8]

I was just wondering, what is that will actually wear/tear on your typical jet engine when you don't warm it up properly.

I'm no engineer, but our FCOM says it's "to increase EGT margins for takeoff," whatever that means.

[Phil Bunch]

A slightly related question,:

Do lubricants exist for marine diesels or turbine engines that are similar in composition and/or performance to synthetic oils as used in modern automobile piston engines? 

In the USA, a popular brand is "Mobil 1", and it is said to provide substantially less cold weather warmup sensitivity for gasoline-fueled piston engines.  In other words, it provides good lubrication much quicker in the winter, sticking to engine parts after engine shutdown.  It is aldo advertised to last longer between oil changes, easier engine starts, etc.

[Jeroen Hoppenbrouwers]

Strange. From cold start early morning to temp reading showing operational temp in about 30 seconds.


Hoppie

[Phil Bunch]

There is some technical information here about Mobil's latest turbine oil, linked as a PDF from this web page:

http://www.exxonmobil.com/en/aviation/products-and-services/products/mobil-jet-oil-387

"The closely controlled viscosity of Mobil Jet Oil 387 at -40°C (-40°F), and a pour point below -54°C (-65°F), ensure the good low-temperature fluidity which permits starting and lubrication at temperatures as low as -40°C. In extensive laboratory testing, Mobil Jet Oil 387 exhibits excellent bulk oil stability at temperatures greater than 225°C (437°F)."

"Permits start-up and ensures effective lubrication of critical components (such as APUs in ETOPS applications) at temperatures as low as -40 °F"
-----------------

As an ignorant person regarding jet engines, I found these basic tutorials on jet engine lubrication to be helpful:

http://www.exxonmobil.com/en/aviation/knowledge-library/resources/jet-engine-oil-system-1

http://www.exxonmobil.com/en/aviation/knowledge-library/resources/jet-engine-oil-system-2

[Jeroen D]

Strange. From cold start early morning to temp reading showing operational temp in about 30 seconds.

Well, as you live in Florida I would think the average ambient temperature is not that far off from the normal operating temperature.

But seriously, on modern engines, especially diesels, if you find yourself at temperatures below 0oC starting and leaving it to idle will hardly move the needle so to speak. This is where engine will have the most wear. Cold cilinder liners, cold oil. (and of course terrible for the environment). Better to immediately drive of a keep the RPM's in check for the first 10-15 minutes.

This is one of the reason that, on average, cars that have been doing mostly city driving versus high way driving (i.e. relatively more (cold) starts tend to have more wear.

Jeroen

[IefCooreman]

General Boeing aircraft: oil temperature is a requirement, warm-up time is a recommendation as it only has a long-term effect.

Warm-up time recommendation is related to differences in "expansion" speeds in the engine leading to more friction and rubbing in the compressor-turbines section. Basically the rotating sections will thermally expand faster than the static case around it, leading to rubbing and friction. The case is designed for this process, it's how a new engine is naturally "fine-tuned" and leaks between blades and case are kept minimal (hence the 2/3/4/... minutes rules for close to idle power). However, application of high power on a cold engine (cold hence smaller radius case compared to top of the blades radius) will rub the blades extra and increase the leaks between case and blades. So in the long term, the engine on-wing time (visible via the EGT margin) is reduced.

[Jeroen D]

Thanks Ief,
So in essence more of less similar to reciprocating engines; Effects from thermal shock (i.e. components having different temperature expansion properties and the usual stuff around lube oil temp.

Just that on a jet engine you appear to be good to go in minutes, rather than hours.

Jeroen