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  #1  
Old 04-05-2016, 12:14 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
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Default First Starts - Crankcase condensation-a data point

FYI - There are dehydrator threads, and water collection in the oil separator threads and winter flying threads. All relate to water/moisture in the crankcase and corrosion issues.

As a datapoint, yesterday I helped (watched) a 10 friend with his first engine start. We checked for leaks then cowled and he did some taxi runs to break-in the brakes. All went well. With 2100 rpm mag checks and such - I guess it was 45 min of running (correction 20 min). Very little at idle and it was preheated to 145F with a Reiff preheater system overnight. OAT was 40F with wind. Oil temp at end of testing was 165F

I have been looking at dehydrators and cobbled one together for experimentation. I thought it would be good to use on a first start because, it is cold, short run, rich and expected some blowby.

Post run, we hooked the dehydrator, powered with a little aquarium pump, the dry air into the breather pipe and moist air out the oil fill tube (540).

About an hour later, there was water collecting in the exit hose. The warm, moist air was condensing water in the hose! - He estimated 1.5 tablespoons!

We were both shocked to see that much water. The desiccant was not weighted or measured, but surely there was more water coming out via adsorption.

Now you know, definitively, how much water you could leave in the crankcase for a short engine run. Decisions about dehydrators, water returning to crankcase via oil separators and such are left to other treads, but everyone about to expose your expensive new engine to a joyful first start should take note of this situation.
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Last edited by BillL : 04-06-2016 at 11:36 AM. Reason: entered actual time run.
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  #2  
Old 04-05-2016, 02:07 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by BillL View Post
FYI I guess it was 45 min of running.
It sounds like it was very humid conditions, but at this point I think there should be more concern about the effect all the ground running will have on ring/cyl break in than the amount of moisture that was in the engine.
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  #3  
Old 04-05-2016, 03:19 PM
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Dbro172 Dbro172 is offline
 
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45 minutes of running seems like an extremely long time for a first engine start, especially with the cowl on. How high did the CHTs go?
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  #4  
Old 04-05-2016, 04:07 PM
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maniago maniago is offline
 
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Default Dehydrators are BS

I own a scuba compressor. Desiccant doesn't work effectively the way its being used here.
In general, we run on the order of 3000psi air over desiccant in order to get it to pull out the final bits moisture from the air for scuba purposes - prior to that its done by mechanical separation. The main point is desiccant requires high gas dwell time. That's done by high pressure and a small amount of air being essentially trapped in the desiccant path for a long time, then being allowed to exit.

The underlying theory of pumping dry air into an engine to try to evacuate moist air is fine. But the assumption here is that ambient air is at least equal in water content to the air in an engine. That is false. And even if it weren't false, the % of water content taken out of the air by running huge volumes of air thru a desiccant at ambient pressure in this fashion is minuscule. Its not doing what people think it is. It picks up a little, yes - because desiccant beads are just a chemical sponge. But they are very very little sponges not kitchen sponges.

What is happening is that large volumes of already dry ambient air (dry compared to whats inside the engine) is being forced through the sump. Thats enough to do the job expected here.

Don't believe me? How bout this. Get out of the pool in Florida and stand under a ceiling fan. Do you dry off faster? Yup. Forget that Florida is wet air already. Its drier than your pool body.

On the old thread someone suggested a shop vac to pull the moisture out. That makes sense, tho shop vacs are not explosion proof, so that's a nono. But pumping hot air thru the engine, like from hairdryer, yeah that would make sense, with careful attention to not over pressurize the crank case.
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Last edited by maniago : 04-05-2016 at 04:11 PM.
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  #5  
Old 04-06-2016, 07:47 AM
BillL BillL is offline
 
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Default This is data, implications are your department.

Quote:
Originally Posted by rvbuilder2002 View Post
It sounds like it was very humid conditions,
40F ambient not a cloud in the sky, cold wind from the north. Don't know the DP.
Quote:
Originally Posted by Dbro172 View Post
45 minutes of running seems like an extremely long time for a first engine start, especially with the cowl on. How high did the CHTs go?
Cowl off for first few minutes. Used Lycoming recommendations for first data checks. CHT's overall less than 300F

All can draw your own conclusions on how to use the data. Maybe it was not 45 min, maybe it was 30 min (ok corrected to 20 min), I did not measure it, but this first start will now sit for 30 days while airworthiness, final pilot transition training and other systems/paperwork are completed.

Oh - desiccant - granted different types will lower the moisture to different relative humidity levels. The air was recirculated (slowly, very low space velocity), we just want the RH lower than 100%. 3 lbs of indicating silica gel was used. The Equilibrium Moisture Content / Relative Humidity Isotherm chart shows that low RH will be maintained for low EMC. You are right, for continued use, the EMC could not be allowed to increase to saturation, but we don't need it truly dry like a scuba tank. How low should the RH be? Another research study, not gonna happen.

Remember, this was a first start. The engine could not be heated thoroughly like a cruise flight. It will sit there waiting for the DAR, sign-off, flight training etc. Maybe 4 weeks. Honestly, it probably would not have done irreparable harm to have left it, but did it reduce the inception and progression? Who knows, with special oils maybe not, but mineral oil and no additives? For $20 of parts, vs a $40,000 engine, did it hurt? - no, did it help? absolutely. How much? -open for debate.

So much emotion, so little facts and data. Please, not in front of the newbies.

Meanwhile, this data stands.
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Last edited by BillL : 04-06-2016 at 11:37 AM.
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  #6  
Old 04-06-2016, 09:02 AM
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bret bret is offline
 
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Just last week we put our street sweeper back in service from the winter, it has a 4 cycl Cat Diesel pony engine for the large fan, over the winter we start it once a month and shut it down. so... last week when I fired it up I raised the hopper and ran the engine at high idle, after 15-20 min I saw large amounts of steam coming from the engine, as I walked up to it I thought it had a radiator leak or something then I saw huge amounts of steam and water dripping out of the crankcase breather hose! moisture and water boiling out of the engine oil and crankcase!
So there are two contradicting missions for your engine run, One, you want the oil to get hot enough to boil off the water content, but, Two, you don't want the cylinders and rings to get hot and glazed over before you do a proper high load run to seat the rings.
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  #7  
Old 04-06-2016, 09:41 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
It sounds like it was very humid conditions, but at this point I think there should be more concern about the effect all the ground running will have on ring/cyl break in than the amount of moisture that was in the engine.
One of the byproducts of hydrocarbon combustion is H20. Because the internal space of an engine is filled via blow-by gases, post-combustion, the air in there is always moisture laden.

You can see this when you first start your car. The exhaust pipes and muffler fill with water before they become hot enough to keep it from condensing/heat induced vaporization. When a car is still warming up, you can see water pouring out of the tail pipe at a stoplight.

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  #8  
Old 04-06-2016, 09:51 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by BillL View Post
So much emotion, so little facts and data. Please, not in front of the newbies.
Well, you didn't quote my post regarding an extended ground run, but it actually was for the newbies..... (keep them from thinking this is a good idea).

A first engine run (regardless of your position on doing it a year before first flight or as late as possible) for more than just a couple minutes at very low power to allow for confirming correct operation of instrumentation and confirm no leaks, is a bad idea.

If a cooling shroud (as shown on page 10 of THIS DOCUMENT) is used so that the engine can be run at maximum continuous cruise power, then an extended ground run would not be detrimental.
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  #9  
Old 04-06-2016, 10:19 AM
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Mel Mel is online now
 
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Aircraft cooling systems were NOT designed for extended ground runs. They are designed for in-flight cooling. Running on the ground does NOT produce balanced cooling for the cylinders. ESPECIALLY on a brand new engine.

Someone noted before (post was deleted) that this extended ground running of the engine can and will, in most cases, cause cylinder glazing.
They also noted that they had not been wrenching on Lycomings for 45 years. Well, I have. And it is fact, not emotion.
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Last edited by Mel : 04-06-2016 at 10:33 AM.
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  #10  
Old 04-06-2016, 10:56 AM
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MarkW MarkW is offline
 
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Hey Bill,
Not wanting to pile on here but to help a little with the data point.
I have to assume some things here as the initial process is a little vague.
If you are pumping 165 degree air into a tube surrounded by 40 degree ambient air you will get condensation no matter how dry the 165 degree air is. (within reason).
Example= 120 degree air at 20% (very dry air) has a DP of 65-70 degrees.
100 degree air at 50% RH is has a DP of 75-80 degrees.

You have basically set up a system similar to a refrigerated air dryer used on a compressor.

I have no doubt the engine developed a large amount of water.

http://www.uigi.com/UIGI_IP.PDF
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