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Engine Dryer Data Collection

dpansier

Well Known Member
My home constructed open loop engine dryer has been in use for over 1 year and I assume it provides a benefit but without the data, I’m just guessing.

The purpose of the test is to determine the residual humidity level after a 4 hour flow of dry air into the engine crankcase confirming the internals are staying dry between flights.

Engine dryer sequence of operation, high volume air for 3 minute purge to evacuate the wet air followed by 4 hours of filtered dry air.
A mattress type inflator provides the high volume purge air.
A aquarium pump provides the low volume dry air at 4 Lpm after passing thru desiccant beads and filter.

The temperature and humidity data was collected with a Elitech GSP-6 sampling at a 10 minute rate.
The temperature and humidity probes are attached to a plastic rod and cap allowing the sensors to be inserted into the dip stick tube about 1” above the oil level.
The cap seals tightly to the dip stick tube and also has a fitting allowing the passing of dry air into the engine.

Not shown in the graph, inserting the probe immediately after a flight shows a 98% humidity level in the crankcase.
 

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Thanks for sharing. I've used a home made engine dryer for many years without quantitatively knowing how well it works. I figured if the science and engineering were good then it's probably helping. I have a humidity sensor in the container with the desiccant. When the sensor reads above 40% I change out the desiccant. I use two aquarium pumps in parallel; a high volume piston and low volume vibrator. I run the piston pump for an hour after flying and the vibrator runs continuously.

I verify the plumbing connections with the dipstick and breather by a two-way value that dumps air out of the breather rather than cycling it back to the desiccant container. If the dumped air produces bubbles when the tube is inserted into water then I know the there are no major air leaks.
 
Great information guys! I too wanted to quantify the effect of engine dehydration and try to show with data that it is effective in maintaining a drier atmosphere in the engine crankcase. My graphs show data collection in the oil filler tube on a Lycoming O-360. My system is simple with a single sealed pump pushing dual filtered air into the breather and extracting it from the oil fill tube. It’s a closed loop system which extends the life of the media between rejuvenation. Also I wasn’t happy with the cost of available systems so inline with Einstein’s philosophy of everything should be a simple as possible but no simpler, over time I developed the Mojave System.

www.rbaviation.com/mojave

Here are a couple of my data graphs.
 

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My home constructed open loop engine dryer has been in use for over 1 year and I assume it provides a benefit but without the data, I’m just guessing.

The purpose of the test is to determine the residual humidity level after a 4 hour flow of dry air into the engine crankcase confirming the internals are staying dry between flights.

Engine dryer sequence of operation, high volume air for 3 minute purge to evacuate the wet air followed by 4 hours of filtered dry air.
A mattress type inflator provides the high volume purge air.
A aquarium pump provides the low volume dry air at 4 Lpm after passing thru desiccant beads and filter.

The temperature and humidity data was collected with a Elitech GSP-6 sampling at a 10 minute rate.
The temperature and humidity probes are attached to a plastic rod and cap allowing the sensors to be inserted into the dip stick tube about 1” above the oil level.
The cap seals tightly to the dip stick tube and also has a fitting allowing the passing of dry air into the engine.

Not shown in the graph, inserting the probe immediately after a flight shows a 98% humidity level in the crankcase.

Thanks for the data Don this is very helpful. I was assuming saturation and condensation pretty soon after shutdown as the engine cooled. That is why I started the high flow purge. I use a check valve to prevent back flow into the desiccant bed so only one hose goes to the engine. Calculations for 4 lpm and based on 4 gallon crankcase volume indicate 98% displacement in ~30 min.

What I have been wondering, is if there is any liquid in there that would evaporate and drive the humidity back to saturation. Crude testing indicated it was not likely but it was not a continuous data plot like you have, that is perfect.

Will you be running the test for a longer period, say a week, to confirm the crankcase stays dry?

Mac - - excellent question, but it may be more about premature issues and a higher cost for components at overhaul. Or we could just fly more frequently (like Vlad) and it would last much longer. We do know that low humidity will drastically reduce, or stop corrosion, and that (slipper) camshafts are one of the weak links. Not sure about the roller type. Personally, I just don't like guessing about the efficacy of a tool. It's fun and educational :) If we all keep this up someone just might end up with TBO information.
 
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Thanks for the comments, I plan to continue collecting data and will add to this thread in the future.

Jeff requested data on the humidity level without introducing dry air but I see John has captured that in his first graph so I will focus on measuring the longer term retention levels after running the sequence described in my first post.

I went open loop because the breather tube is not accessible from the outside of the cowl and as others have stated, it is quick to attach and get functioning.

Appears the purge function is worth while as it significantly reduces the moisture level prior to introducing the dry air.

I will report back once I gather one week of after purge data.
 
Anyone have data for an actual rate of corrosion at standard atmosphere (59F) in the presence of water vapor only, no liquid water?

One might argue all the value is in the initial high flow purge, while the low RH provided by the long term desiccant flow is overkill.

Interesting paper here, measured oxidation of 1020 steel samples at 149F. Corrosion rate is flat below roughly 75% RH:

https://www.osti.gov/servlets/purl/208358
 
I have been running the low RH air for 4 hours after the purge to minimize the moisture, it may be overkill but after reading this SAE technical paper I though I would continue till I capture additional data.

I am not a SAE member so I do not have access to the full report.

https://www.sae.org/publications/technical-papers/content/250030/

Paper is dated 1925. I'd bet sulfur content was higher in fuels back then. Current spec for 100LL is 0.05% by mass.

No doubt we can push RH way down. The question is how low it needs to be. I'm curious because if all it takes to get most of the benefit is a few minutes with a airbed pump while wiping bugs, well...
 
Paper is dated 1925. I'd bet sulfur content was higher in fuels back then. Current spec for 100LL is 0.05% by mass.

No doubt we can push RH way down. The question is how low it needs to be. I'm curious because if all it takes to get most of the benefit is a few minutes with a airbed pump while wiping bugs, well...

Perhaps we can send what we want to test to the PF guy - he's always itching for a new thing to test.

https://www.youtube.com/watch?v=UoijjWUGU2Q
 
Mac - - excellent question, but it may be more about premature issues and a higher cost for components at overhaul. Or we could just fly more frequently (like Vlad) and it would last much longer. We do know that low humidity will drastically reduce, or stop corrosion, and that (slipper) camshafts are one of the weak links. Not sure about the roller type. Personally, I just don't like guessing about the efficacy of a tool. It's fun and educational :) If we all keep this up someone just might end up with TBO information.

Oh, I'm a believer, especially at the negligible cost of making one of these things. My RV-9A is hooked up 24/7, and has been since I bought the plane, pumping air at 11-14% RH (was 11% this afternoon when I looked at it). I also am confident that moisture sitting around in an engine leads to corrosion and that corrosion leads to $$$. Using that empirical data, I inductively reason that dehydrators are a good thing for airplane engines. I just can't prove it...;)

I do agree that it's fun and educational, and that's a good thing too.
 
Paper is dated 1925. I'd bet sulfur content was higher in fuels back then. Current spec for 100LL is 0.05% by mass.

No doubt we can push RH way down. The question is how low it needs to be. I'm curious because if all it takes to get most of the benefit is a few minutes with a airbed pump while wiping bugs, well...

I don't think so Dan, at best purge equals ambient humidity then it can easily drop below dew point depending on weather and geographic location, but it is way better than remaining saturated!

Humidity means, #H2O per # of dry air, humidity is relative to saturation at a specific temperature.

For the last week I have spent some time (hours on Google scholar) looking for your answer. I found one reference in a quick view of a textbook on corrosion that below 35% RH, raw untreated carbon steels will not corrode. I shall continue to look. Acidity should be neutralized by oil additives for the period we use them and 100LL. Longer is another matter.
 
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I'm curious because if all it takes to get most of the benefit is a few minutes with a airbed pump while wiping bugs, well...

I returned from a flight today and purged for 8 minutes with no dry air flow, will the purge alone provide a benefit? Field conditions at the time of the purge was Temp 56, Dew Point 45, Humidity 67%
Data collection in process and I will down load the results in a few days.
 
I don't think so Dan, at best purge equals ambient humidity then it can easily drop below dew point depending on weather and geographic location, but it is way better than remaining saturated!

Humidity means, #H2O per # of dry air, humidity is relative to saturation at a specific temperature.

For the last week I have spent some time (hours on Google scholar) looking for your answer. I found one reference in a quick view of a textbook on corrosion that below 35% RH, raw untreated carbon steels will not corrode. I shall continue to look. Acidity should be neutralized by oil additives for the period we use them and 100LL. Longer is another matter.

My home ranges from 30-50% relative humidity throughout the year. I have numerous pieces of unfinished mild steel that have sat in the house for decades. Not a speck of corrosion on them. Even the steel that sits in the garage, with much higher humidity levels in the summer, show very little corrosion over countless years. I suspect that it is not the humidity causing corrosion in our engines, but instead condensation from the regular temp swings, putting liquid water on parts. Sorry, just speculation and empirical data.

On the flipside, one winter I used a kerosene heater a lot in the garage, substantially raising humidity levels in the closed space. That spring I noticed several tools had developed a slight amount of surface corrosion.

Larry
 
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I suspect that it is not the humidity causing corrosion in our engines, but instead condensation from the regular temp swings, putting liquid water on parts.

My theory too, more or less, the big temp swing being the cooldown from around 200F. Lot of water in 200F air, so replace it with outside air. Even if high RH, the outside air is (1) holding a lot less water than the displaced air, and (2) won't condense any to liquid unless the engine temperature drops below the current ambient temperature.
 
No doubt we can push RH way down. The question is how low it needs to be. I'm curious because if all it takes to get most of the benefit is a few minutes with a airbed pump while wiping bugs, well...

I think that for most of the country it's not the ambient humidity that causes corrosion, it's the it's the condensation from normal temp swings where the temp crosses the dew point.

This calculator illustrates the relationship between temp and dew point. It my rationale for the dehydrator. I could just leave the block heater on 24/7 (or some other way of keeping the whole engine above the dew point at all times), or I could just drop the humidity inside the engine with the dehydrator (much cheaper).

http://www.dpcalc.org/
 
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Question for those collecting data……

Wondering if there is any /enough air movement, if there isn’t a air/oil separator in the vent line, and the dipstick is pulled out, such that natural air exchange would make a significant drop in relative humidity over the first 30 minutes or so after shutdown….. I.e. is it worth it to do it away from home base

Meanwhile, I’ll continue with the air pump while at home base
 
My thoughts on all the continue pondering about the cause of the moisture, or whether simply blowing it all out after a flight would be good enough is this. (Kind of similar to a comment MacCool made above)

My latest engine purchase was over $51,000. The dehydrator is producing a humidity of roughly 11-15%. A premature engine overhaul is so incredibly expensive, and inconvenient, that I don't even care to look for "good enough" in data, when it's this simple and cheap to get a real good humidity level. It's an unnecessary waste of thought. It takes 30 seconds to hook up after a flight, and less than that to pull it off before the next. In fact, if a dehydrator on it's own wasn't good enough, I'd even consider a nitrogen purge after a flight before I fire up the dehydrator. The engine costs are just too astronomical to not put in this very very minor effort. I have a 5 minute tracking of my hangars humidity recorded over > 1yr, and I know the humidity ranges from 40-75% over much of the year, and near 100% at times. If this saves me even one pitted cam lobe, it'll be worth every bit of effort.
 
Wondering if there is any /enough air movement, if there isn’t a air/oil separator in the vent line, and the dipstick is pulled out, such that natural air exchange would make a significant drop in relative humidity over the first 30 minutes or so after shutdown….. I.e. is it worth it to do it away from home base
...
I do this - it's a simple thing to do, and certainly can't hurt. I also saw a video from the camguard guy where he also said he does it. He knows more about engine corrosion than pretty much anyone.

On a hot day, opening the oil door gets cool air into the cowl quicker, and on a cold day it lets you warm up your hands. Can't go wrong! :)
 
to add onto "Google scholar" information ;
do a search on u-tube for "The USN Mothball Fleet - Storing up for a rainy day ", " 43.33 min. long "
and i think somewhere in the story line (at 29.30 min ) there is a statement on how low ( in % percentage )
(below 30% ) the inside air is kept down to, in the stored ships.
the high lights of the u-tube are at;
29.30 min. " % percentage" and at
33.00 min. " moisture " and at
37.30 min. "air circulating " and at
38.20 min. "heating & drying ",and at
40.00 min. "cost " and at
42.00 min. " at the start of the Korea WAR , and how well the system worked
....
good day to all rick
 
I think you will get good results from simply blowing the moisture out of the crankcase after flying, or at least, blowing out the moisture+oil mist before hooking up the dehydrator.

After I fly, I use an air mattress pump on the oil-filler to blow the moisture out of the engine. It will blow visible moisture out the breather for about 15 seconds. That's moisture that would have condensed in the engine. If you're using a dehydrator, it will also prolong the dryness of the dessicant and keep it from getting oily.
 
On the flipside, one winter I used a kerosene heater a lot in the garage, substantially raising humidity levels in the closed space. That spring I noticed several tools had developed a slight amount of surface corrosion.

Larry

This is the key, Larry, leaving combustion products in the crankcase. I wonder what the pH of the water condensed in the engine is in presence of sulfur oxides? We still have sulfur in 100LL but not much, 0.05% S, just like kerosene.
 
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On the flipside, one winter I used a kerosene heater a lot in the garage, substantially raising humidity levels in the closed space. That spring I noticed several tools had developed a slight amount of surface corrosion.

Larry

This is the key, Larry, leaving combustion products in the crankcase. I wonder what the pH of the water condensed in the engine is in presence of sulfur oxides? We still have sulfur in the fuel but not much, 0.05% S. Just like kerosene.
 
SNIP I suspect that it is not the humidity causing corrosion in our engines, but instead condensation from the regular temp swings, putting liquid water on parts. Sorry, just speculation and empirical data.

SNIP

Larry

Larry - you are correct. Corrosion does not happen without liquid state and some sort of electrolyte. For example, a tiny spec of salt on a surface will absorb water and cause corrosion locally, even if the base metal is above the dew point and appears macroscopically dry. I believe many contaminants can act as electrolytes, to what degree I don't know.

The key, as you and others have noted, is to purge the very moist vapor in the crankcase upon shutdown, and then to be sure that the engine temperature is always above the dewpoint. This can be done by either heating the engine in its entirety, or by injecting air with a dewpoint that is always lower than the engine temperature.

I've been accomplishing this the last 20 years by simply displacing the oil dipstick up and to the side after each flight. The oil filler tube acts as a chimney, transporting the heated gas inside the engine up and out, drawing in much dryer air through the breather. One can see the stream of visible moisture coming out. Additionally, in the winter I keep the entire cowl blanketed and heated to about 60F.

One potential problem with blowing desiccated air into the engine in an unheated hangar would be if the desiccant gets saturated, yet the blower continues to blows air into an engine which is colder than the dewpoint. This can happen after a clear winter night, when the hangar and aircraft have cooled to below the dewpoint (i.e., frost on the hangar roof).
 
By request I collected the data on a purge only, shown on the left side of the chart, the purge was about 8 minutes while I wiped down the plane after flight.

The right side of the chart depicts data after a 8 minute purge and 4 hours of dry air.

The data indicates a significant reduction in the dew point using the purge followed by dry air.
 

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