A320: Confusion about IDG oil and Engine oil

[pineteam]

Hello guys,

While reading the FCOM about the ECAM advisory conditions for the engines regarding the Oil Temperature it’s written”In addition, an increase in oil temperature could be related to the IDG oil cooling system. To reduce oil temperature, before limits are reached, the following are recommended:
1. Low Speed- Increase engine speed to increase fuel flow and thereby cool IDG oil.
2. High Speed- Reduce generator load or turn off generator. If the oil temperature continues to rise, mechanically disconnect the IDG.

From what I understand: Engine has it’s own oil sytem and IDG has its own oil system and they are independent. So why the IDG oil cooling system can have an effect on the engine oil temperature?
Thank you.

[Chesty Morgan]

Which engine?

[pineteam]

IAE V2500 and PW1100G in our fleet. The FCOM advisory is the same for both regarding Engine Oil Temperature.

[jimjim1]

to increase fuel flow and thereby cool IDG oil.

To be clear, I have no information on these specific engines.

However, it would appear that the oils are fuel cooled. If the IDG got first bite at the cooling fuel flow, before the engine oil or maybe simultaneously, then this would appear to explain the statements from the books.

[Goldenrivett]

However, it would appear that the oils are fuel cooled. If the IDG got first bite at the cooling fuel flow, before the engine oil or maybe simultaneously, then this would appear to explain the statements from the books.
You are correct. DSC 70-41 Fuel System shows an oil cooing diagram with IDG cooling taking place before that warmed fuel goes to the engine oil cooler heat exchanger. See Oil cooling (http://www.blackholes.org.uk/PP/oil%20cooling.jpg)

[Lantirn]

You are correct. DSC 70-41 Fuel System shows an oil cooing diagram with IDG cooling taking place before that warmed fuel goes to the engine oil cooler heat exchanger. See Oil cooling (http://www.blackholes.org.uk/PP/oil%20cooling.jpg)

That makes a lot of sense.

However what doenst make sense here is that, in QRH for IDG oil temp >147 advisory, instructions are only to shed electrics. FF is nowhere here, but it should as a last resort? Or I guess engine oil would heat last, so you address IDG issues first with electrics.

[aeromech3]

IMO, I think we need the engine oil system diagrammatic, as for sure there is an air cooled heat exchanger (fan duct air) somewhere, mostly the exchangers shown here are primarily to raise the temperature of the fuel to prevent icing. Same goes for the IDG which will have a small amount of oil at very high pressure and hence need a lot of heat dissipation.

[Goldenrivett]

IMO, I think we need the engine oil system diagrammatic, as for sure there is an air cooled heat exchanger (fan duct air) somewhere, mostly the exchangers shown here are primarily to raise the temperature of the fuel to prevent icing. Same goes for the IDG which will have a small amount of oil at very high pressure and hence need a lot of heat dissipation.
See engine oil cooling (http://www.blackholes.org.uk/PP/17juusx.1.png)

FUEL/OIL HEAT EXCHANGER (FOHE)

The fuel/oil heat exchanger uses cold fuel from the Fuel Metering Unit (FMU) to cool the oil. Oil from the lubrication system enters the FOHE, via the Servo Fuel Heater (SFH) and the Air Cooling Oil Cooler (ACOC), and flows around the fuel tube in the matrix.

The FADEC controls the fuel and the engine oil temperature.

IDG COOLING

The Integrated Drive Generator (IDG) fuel/oil heat exchanger enables to cool the IDG oil.

The FADEC controls the fuel and the engine oil temperature.

[tdracer]

Can't speak for brand A, but Boeing has used fuel/oil heat exchangers to cool the IDG oil since at least the 757/767. With the advent of FADEC, the systems have become somewhat more sophisticated (e.g. active control of the oil cooling rather than the earlier passive systems) but the fundamental systems have remained largely unchanged in the last 40 years.

[dream747]

Never quite fully understood this as well.

V2500 - Engine oil is first cooled via the Air/Oil Hear Exchanger before entering the Fuel/Oil Heat Exchanger for another round of heat exchanger. The fuel that cools the engine oil in the Fuel/Oil Heat Exchanger is part of a rather complex system (refer to FCOM diagram) where it also routed to cool the IDG oil.

Based on this I infer that if there’s something wrong with IDG leading to high IDG oil temperature, it will cause the fuel that comes through to cool it to warm up significantly enough to be inefficient to cool the engine oil effectively when it eventually reaches the Fuel/Oil Heat Exchanger. Hence the procedure to increase fuel flow if possible or reduce IDG loads.