Oil Cooling; Turbocharged Lycoming IO-540
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Oil Cooling; Turbocharged Lycoming IO-540
Hey guys I would like to get your inputs and comments on an issue I am working on. It goes about powerplant cooling tests and more specifically about cooling of the oil in a turbocharged Lycoming IO-540 engine. Our project is to develop an STC whereby we add a turbocharger and new propeller to a Type Certified aircraft.
I’ve noticed from the Lycoming Engine Installation Manual that for the developmental cooling tests both temperatures of the oil into and out of the oil cooler should be measured. This makes sense to me as one could then use this information to establish the efficiency of the oil cooler and the oil cooler arrangement.
However our client is concerned about the possibility of higher oil temperatures elsewhere in the engine, which brings me to my question; is it possible to have localized peaking of the oil temperature elsewhere in the oil cycle, which might lead to thermal degradation of the oil? 
In my opinion, I believe that if we stick to the test requirements and limitations as specified by the OEM for the oil in, oil out all should be well, however, I would like to invite comments from anyone who has experience in this field.
Where do you anticipate the highest temperatures would be? Also, do you think it is possible to exceed of the safe temperature limitations for both SAE-J1966 (Mil-L-6082) and SAE-J1899 (MIL-L-22851) oil? Please keep in mind that the aircraft will be used for skydiving purposes and the abusive nature of such operations (i.e. High power settings for sustained periods, rapid descents and, most likely, improper rundown and shutdown of the turbocharger…
). From the data measured already on the aircraft, I know that the temperature of the oil coming out of the oil cooler during the critical climb test was approximately in the order of 81 degrees C. This is well below red line of 118 degrees. At this stage, I do not know the oil temperature going into the cooler but will measure it shortly.
Thanks,
I’ve noticed from the Lycoming Engine Installation Manual that for the developmental cooling tests both temperatures of the oil into and out of the oil cooler should be measured. This makes sense to me as one could then use this information to establish the efficiency of the oil cooler and the oil cooler arrangement.
However our client is concerned about the possibility of higher oil temperatures elsewhere in the engine, which brings me to my question; is it possible to have localized peaking of the oil temperature elsewhere in the oil cycle, which might lead to thermal degradation of the oil? In my opinion, I believe that if we stick to the test requirements and limitations as specified by the OEM for the oil in, oil out all should be well, however, I would like to invite comments from anyone who has experience in this field. Where do you anticipate the highest temperatures would be? Also, do you think it is possible to exceed of the safe temperature limitations for both SAE-J1966 (Mil-L-6082) and SAE-J1899 (MIL-L-22851) oil? Please keep in mind that the aircraft will be used for skydiving purposes and the abusive nature of such operations (i.e. High power settings for sustained periods, rapid descents and, most likely, improper rundown and shutdown of the turbocharger…
). From the data measured already on the aircraft, I know that the temperature of the oil coming out of the oil cooler during the critical climb test was approximately in the order of 81 degrees C. This is well below red line of 118 degrees. At this stage, I do not know the oil temperature going into the cooler but will measure it shortly.Thanks,
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Since the cooler inlet temp is an average of all the individual scavenge temps from crankcase, rockers, etc. there certainly will be some scatter among these temps.
If you're genuinely concerned about localized hot spot temps why not ask Lycoming for their advice? They must have a good idea what the hotter areas are likely to be, and how to measure them.
Once you know the cooler effectiveness you'll have a good idea how much margin exists. (Dumb questions - is the 118 redline for supply, or for scavenge? And what ambient temp were you running?)
If you're genuinely concerned about localized hot spot temps why not ask Lycoming for their advice? They must have a good idea what the hotter areas are likely to be, and how to measure them.
Once you know the cooler effectiveness you'll have a good idea how much margin exists. (Dumb questions - is the 118 redline for supply, or for scavenge? And what ambient temp were you running?)
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I would have thought that every pilot flying a turbocharged aircraft (or driving a turbocharged car) would be aware that the engine should be run for a period of time at tickover speed to enable the oil in the turbocharger bearings to cool before switching off. More turbo failures are caused by not following the above advice than by any other cause.
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I agree that the manufacturer of the engine is the best source for that kind of information. I have done a number of new engine installations, and in my opinion the oil temperature limit as specified by the manufacturer has some margin to allow for local hot spots. The oil can handle that. If the oil temperature does not exceed the limit in the location the engine manufacturer has specified for measuring it you should be ok. I would have more concern about the exhaust system and the cylinder heads for this installation and proposed operation. Turbocharging adds a lot more heat to the engine compartment. As an example of engines I'm familiar with, there is a normally aspirated model which was turbo-superchaged by the manufacturer without a change in cooling devices (same cooling fins on the heads and same oil radiator). In order to keep this engine cool in climb, the full power, full rich fuel flow had to be increased by 25%! An airplane with that turbocharged engine I have flown a lot for tests which put similar thermal stresses as skydiving operation on it has soon shown exhaust system cracks (after about 300 h). We had no problems with the oil.
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One of the critical things on a turbo'ed engine is the correct cooling periods on shutdown, if not done correctly you get oil for want of a better word caramalising in the turbo and its lines, resulting eventually in reduced oil flow and oil starvation.
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I am not sure if I agree that Lycoming themselves are the best source of information. Over the years I have dealt with many such problems, particularly with Para, Glider Tug, Crop dusting and aerobatic aircraft. The engine manufacturer lays down the limits, it is then up to the aircraft manufacturer to see that those limits are met. The aircraft manufacturer makes the cowlings, sites the oil coolers and the cooling baffles. So the aircraft manufaturer are more probably the people you should talk to. Having said that I have often found that the aircraft manufacturers are sometime surprised at what thier aircraft are being used for and in many cases not what they were initially designed for. I have worked on many different types used for glider towing that were clearly not meant for the purpose.
Siting of the oil cooler is particularly important. A typical fit might be inside the cowling fed by engine cooling air before it is exhausted through the cowl flaps or whatever. Engine cooling air by this time is already hot from cooling the engine, and thus doesn't cool the oil too well. On many occations I have modified Lycoming powered aircraft with a second oil cooler placed in the forward intake baffle in front of the rearmost of the two front cylinders. This modification was also carried out on numerous Pitts aircraft fited with both the IO-360 and IO-540. If this is already the position of your oil cooler then consider siting another in the way mentioned above, inside the cowling. There is sometimes more room inside the cowling that you can fit an oil cooler of almost double the size of the one at the front.
With glider towing and Para aircraft the real danger is in the sudden cooling of the cylinders in an idle power decent. The cylinders will crack. I have known the whole head to come off from the barrel, in fact the CAA still use it as an exibit! Aslo new engines or engines with overhauled reciprocating gear will run significantly hotter untill they are well run in, thus giving you the hot spots you describe. A further note is to consider ambient air temperature. Check your temperatures on the hottist of days and not when it's cold and raining!
Hope that this has been helpful.
Siting of the oil cooler is particularly important. A typical fit might be inside the cowling fed by engine cooling air before it is exhausted through the cowl flaps or whatever. Engine cooling air by this time is already hot from cooling the engine, and thus doesn't cool the oil too well. On many occations I have modified Lycoming powered aircraft with a second oil cooler placed in the forward intake baffle in front of the rearmost of the two front cylinders. This modification was also carried out on numerous Pitts aircraft fited with both the IO-360 and IO-540. If this is already the position of your oil cooler then consider siting another in the way mentioned above, inside the cowling. There is sometimes more room inside the cowling that you can fit an oil cooler of almost double the size of the one at the front.
With glider towing and Para aircraft the real danger is in the sudden cooling of the cylinders in an idle power decent. The cylinders will crack. I have known the whole head to come off from the barrel, in fact the CAA still use it as an exibit! Aslo new engines or engines with overhauled reciprocating gear will run significantly hotter untill they are well run in, thus giving you the hot spots you describe. A further note is to consider ambient air temperature. Check your temperatures on the hottist of days and not when it's cold and raining!
Hope that this has been helpful.
