Engine Dehumidifier DIY

Huckster79 said:
The air conditioning type won’t really work if we are t in a heated hanger would they? I’m interested to see the membrane type when I can get on computer later...
Click to expand...

Nah, think about it. The air conditioned hanger has already removed some of the moisture, so the cooling type will actually work better. ACs do remove humidity, but only a certain percentage.

In a pinch, I've operated my transmitter sites without the desiccant. The building air conditioner removes a lot of moisture, and a compressor with a big tank will condense a lot of the moisture itself. (Just have to remember to drain it regularly.)

Again: I'm no engine expert, but thinking out loud ... I'm not sure you need air at a sub-zero dewpoint. I just don't know.
 
Stephen Poole said:
Nah, think about it. The air conditioned hanger has already removed some of the moisture, so the cooling type will actually work better. ACs do remove humidity, but only a certain percentage.

In a pinch, I've operated my transmitter sites without the desiccant. The building air conditioner removes a lot of moisture, and a compressor with a big tank will condense a lot of the moisture itself. (Just have to remember to drain it regularly.)

Again: I'm no engine expert, but thinking out loud ... I'm not sure you need air at a sub-zero dewpoint. I just don't know.
Click to expand...

Oh I agree if you are in a air condidioned hanger... or heated hanger. But for me I’m not.. the AC type dehuey that cools the air then heats it to dehumidify it wouldn’t work in a hanger that’s cold as those units will freeze up if they are in the cold is what I was thinking...
 
Huckster79 said:
The air conditioning type won’t really work if we are t in a heated hanger would they? I’m interested to see the membrane type when I can get on computer later...
Click to expand...

The refrigerated types don't have a compressor; they're basically just a long tube that goes through a cooling chamber. If it's cold in the room, the refrigeration doesn't cut on. They're designed for LOTS of CFM, though ... you could do something simpler with a little portable refrigerator. Drill holes in the sides and pass your own copper coil through it.

(The Revenooers are likely to think you're making your own wildcat whiskey, so hide it!)

Yeah, for what you're doing, either desiccant with a filter or membrane is the way to go. I'd say desiccant with a really good particulate filter before it hits the engine -- in other words, what you've already built. Just add a good microfilter cartridge. You can use a water filter from Lowes or Home Depot. Just get the plain-jane fiber cartridge (the one that looks like a molded spool of twine).

You're a man after my own heart, McGuyver. :)
 
Stephen Poole said:
The refrigerated types don't have a compressor; they're basically just a long tube that goes through a cooling chamber. If it's cold in the room, the refrigeration doesn't cut on. They're designed for LOTS of CFM, though ... you could do something simpler with a little portable refrigerator. Drill holes in the sides and pass your own copper coil through it.

(The Revenooers are likely to think you're making your own wildcat whiskey, so hide it!)

Yeah, for what you're doing, either desiccant with a filter or membrane is the way to go. I'd say desiccant with a really good particulate filter before it hits the engine -- in other words, what you've already built. Just add a good microfilter cartridge. You can use a water filter from Lowes or Home Depot. Just get the plain-jane fiber cartridge (the one that looks like a molded spool of twine).

You're a man after my own heart, McGuyver. :)
Click to expand...

I really appreciate your contributions to this thread as you brought up technology we weren't discussing... I think to add a better filter I need to get a bigger pump... right now I have a loose fibrous filter going into the pump tub and the air pump does have a felt material as a filter... However when I added an additional filter in line on the pumped air it cut the flow down to where I couldn't detect it. So I think a larger pump/compressor is necessary.

The membrane is intriguing but the high cfm requirement I think may be disqualifying??? your thoughts? as I don't think we want rushing high volume air through it 24/7. Idk why but it just doesn't seem "right"...

what are your thoughts on a more powerful pump vs using an oilless compressor throttled back post compressor to minimize compressor cycling? I'm torn what would be the better route...
 
Huckster79 said:
what are your thoughts on a more powerful pump vs using an oilless compressor throttled back post compressor to minimize compressor cycling? I'm torn what would be the better route...
Click to expand...

Be careful about using me as a "technical X-Purt" on anything to do with aviation. I'll have your plane flying backwards, upside down, and the strobes will all be a nice shade of purple.

An oilless compressor with a storage tank is ideal. Most of these have a little regulator that you can use to set it to, say, 10-20 lbs (though it's difficult to set really low values). Putting the filter in line will slow the CFM (i.e., the flow), but that may not be a bad thing.

I doubt you'll be able to have a pump directly driving the desiccant, then straight into the engine through the filter. That pump is going to wear out in short order.

Be prepared to replace the compressor from time to time. I've tried about every brand that there is, and every oilless unit that I've bought has eventually failed. This (of course) is dependent on how much it has to run. If you set the regulator just high enough to bubble dry air into the crankcase, the size of the tank will determine how often it cycles and how long it has to run to refill the tanks.

(Sorry, that's common sense. I need more coffee.)
 
Stephen Poole said:
An oilless compressor with a storage tank is ideal.
Click to expand...

Won't the air we put into the engine be quite cool then, though? It'll be heated by compression, and that heat will be lost to ambient while it sits in the storage tank, and then it'll cool down as it's released into the engine?
 
flyingcheesehead said:
Won't the air we put into the engine be quite cool then, though? It'll be heated by compression, and that heat will be lost to ambient while it sits in the storage tank, and then it'll cool down as it's released into the engine?
Click to expand...

Well, duh. Yeah, I missed that in the rest of the thread. Heh.

You want the compressor tank to be cool so that the moisture will condense there. Yes, you'll need a way to warm the air up. I can see that you wouldn't want to pump ice-cold air into your engine.

If I was MacGuyverin' it, I'd just use a spaceheater and some copper coil to warm the air back up. I doubt that would heat the engine block very much, but it would at least keep the air from cooling the block off. (Maybe.)

I done exhausted my thoughts on this one, I s'pect.
 
"Hi, I'm a solution. Is there a problem around here someone could point me to?"
 
flyingcheesehead said:
Won't the air we put into the engine be quite cool then, though? It'll be heated by compression, and that heat will be lost to ambient while it sits in the storage tank, and then it'll cool down as it's released into the engine?
Click to expand...

I’m thinking I could toss the coil under my cowl as it stays in the 80s in there, and mines super accessible with two piano hinged sides...

But if we kept it to a trickle of air would it really make a difference? If it wasn’t enough to cool off the intervals which once they are running in the low 100s a wisp of air I would doubt would do that... and going from cold to warm shouldn’t cause a condensation issue as the cold air can hold even less moisture than warm so even though absolute humidity would remain the same the relative humidity of the piped in air would drop as it heats up.

Just thinking out loud...
 
Why not a theromostatically controlled heater that keeps your engine at 70F (or your temp of choice) permanantly with a 24 hour nitrogen purge after each flight. During the purge, feed 10 CFH of 0% humidity nitrogen for 24 hours. That ought to dry the sucker out and the warmth will prevent condensation once the nitrogen bath ends.

Seems a lot simpler than the dehydration schemes.
 
kyleb said:
Why not a theromostatically controlled heater that keeps your engine at 70F (or your temp of choice) permanantly with a 24 hour nitrogen purge after each flight. During the purge, feed 10 CFH of 0% humidity nitrogen for 24 hours. That ought to dry the sucker out and the warmth will prevent condensation once the nitrogen bath ends.

Seems a lot simpler than the dehydration schemes.
Click to expand...

You may have a very valid point... even with or without the heat that nitrogen bath may be the ticket... certainly worth the discussion...
 
kyleb said:
Why not a theromostatically controlled heater that keeps your engine at 70F (or your temp of choice) permanantly with a 24 hour nitrogen purge after each flight. During the purge, feed 10 CFH of 0% humidity nitrogen for 24 hours. That ought to dry the sucker out and the warmth will prevent condensation once the nitrogen bath ends.

Seems a lot simpler than the dehydration schemes.
Click to expand...

Very good idea. Nitrogen is preferred, as I said. We don't use it because of the expense, and because of the difficulty in getting the canisters delivered to remote transmitter sites.
 
Huckster79 said:
I’m thinking I could toss the coil under my cowl as it stays in the 80s in there, and mines super accessible with two piano hinged sides...

But if we kept it to a trickle of air would it really make a difference? If it wasn’t enough to cool off the intervals which once they are running in the low 100s a wisp of air I would doubt would do that... and going from cold to warm shouldn’t cause a condensation issue as the cold air can hold even less moisture than warm so even though absolute humidity would remain the same the relative humidity of the piped in air would drop as it heats up.

Just thinking out loud...
Click to expand...

Yes, but because cold air holds less moisture, it also won't help draw moisture out of the engine as quickly. So, if going with a compressor setup, it'd be a matter of reheating the air between the tank and the engine.

kyleb said:
Why not a theromostatically controlled heater that keeps your engine at 70F (or your temp of choice) permanantly with a 24 hour nitrogen purge after each flight. During the purge, feed 10 CFH of 0% humidity nitrogen for 24 hours. That ought to dry the sucker out and the warmth will prevent condensation once the nitrogen bath ends.

Seems a lot simpler than the dehydration schemes.
Click to expand...

Not a bad idea at all. I was talking with an experimental owner yesterday who suggested the same thing, and said that a winter's worth of nitrogen costs him less than 100 bucks.

Anyone know of a good (accurate) oxygen sensor that can be used with an Arduino? Maybe I'll go with my oil-cap-with-tube idea, and put sensors for temp, humidity, pressure and O2 a few inches inside, and a display outside.
 
Is tanked nitrogen that cheap? I couldn’t find price online. Was gunna call a plave tomorrow. If ur interested in really investing up front a nitrogen generator can be had for $1000 on up- just pump it to it 24/7...
 
Huckster79 said:
Is tanked nitrogen that cheap? I couldn’t find price online. Was gunna call a plave tomorrow. If ur interested in really investing up front a nitrogen generator can be had for $1000 on up- just pump it to it 24/7...
Click to expand...

Airgas lists it as $59 for a 300 cu ft cylinder - Sounds like that's an exchange or fill price maybe? But I also found new cylinders for $425. So, yeah, cheaper than any of the GA engine dehydrators that I've seen. ;)
 
flyingcheesehead said:
Airgas lists it as $59 for a 300 cu ft cylinder - Sounds like that's an exchange or fill price maybe? But I also found new cylinders for $425. So, yeah, cheaper than any of the GA engine dehydrators that I've seen. ;)
Click to expand...

My lack of experience with aircraft engines means that I have no way to estimate how much nitrogen you'd need. The idea of just using it to fill the crankcase after a flight, with a block heater, seems workable. But that's just a guess.

If you need to fill a coax with nitrogen, I gots all sorts of formulas. The aforementioned 6" line at 101.1 FM is 1300' long, so you're talking tens of THOUSANDS of cubic feet. Using the biggest cylinders available, I went through several of them just to purge the line one time.(!)

Edit: remember, too, that my coax lines are pressurized -- more than one atmosphere. Roughly speaking, you have to multiply the volume by the number of atmospheres that you want in the line. I typically run between 3-15 lbs PSI. That multiplies the amount of gas needed. There's no nitrogen generator available that I can justify on the cost basis.

The nitrogen generator might work, and might be cost-effective in the long run. But then again, I'm so stingy, the desiccant-with-particulate-filter is still the most appealing to me.

Again: speaking from total ignorance ... I wonder if the best solution isn't just to crank the engine and let it run a while at frequent intervals? It's an excuse to fly .. .. ..:D
 
Stephen Poole said:
My lack of experience with aircraft engines means that I have no way to estimate how much nitrogen you'd need. The idea of just using it to fill the crankcase after a flight, with a block heater, seems workable. But that's just a guess.
Click to expand...

And it's more involved than that. Part of the problem is that the only easy entrance to the engine is the oil filler tube, so there isn't any way to pass air through the whole thing. There's going to be some mixing and some diffusion. I'm relying solely on diffusion at a very small port right now, so it would be a big improvement just to put a few cubic feet of nitrogen through it. Using a tube with a hole in one side and the end plugged would probably help stir things up in there - I don't have enough room to actually curve the tube.

Again: speaking from total ignorance ... I wonder if the best solution isn't just to crank the engine and let it run a while at frequent intervals? It's an excuse to fly .. .. ..:D
Click to expand...

I think the whole reason that we're even talking about this is that we can't always do that. :( There have been times where I've had to go 6-10 weeks in between flights in the winter due to weather and surface conditions. It really sucks not being able to fly for that long, but what sucks even more is hurting your airplane in the process. :(
 
flyingcheesehead said:
And it's more involved than that. Part of the problem is that the only easy entrance to the engine is the oil filler tube, so there isn't any way to pass air through the whole thing.
Click to expand...

The crankcase breather gives you a second access point.
 
I’m thinking I’m going to go desiccant and air compressor... I’m thinking of not going overly high tech- especially with ez access to breather- just hook it open for a bit then close it... in summer I could probably put a menards dehuey in a box and pump air from there... wouldn’t work in winter tho in unheated hanger. I’m almost done w my custom insulated cowl cover, all sewn just have to sew in Velcro and one strap and it’s good to go. Then my tinkering time can go to this though may take my time now we are coming into flying season and likely not going to be grounded for weeks on end... if my plane didn’t have a good sized want list I would consider the generator and just blast it open loop with nitrogen 24/7... but that much cash could be airplane upgrades..
 
flyingcheesehead said:
Airgas lists it as $59 for a 300 cu ft cylinder - Sounds like that's an exchange or fill price maybe? But I also found new cylinders for $425. So, yeah, cheaper than any of the GA engine dehydrators that I've seen. ;)
Click to expand...
Probably an exchange or fill price. The tanks usually have a rental cost; when we run out, they take the empty and leave us a filled one. I go though enough nitrogen that I buy a liquid nitrogen tank. $180 buys me 230 liters, and it lasts me a month. I draw off gas to a number of instruments at 60 PSI. It's cheaper than a nitrogen generator for the volumes we need. I'm not counting tank rental in the cost.
 
Cap'n Jack said:
Probably an exchange or fill price. The tanks usually have a rental cost; when we run out, they take the empty and leave us a filled one. I go though enough nitrogen that I buy a liquid nitrogen tank. $180 buys me 230 liters, and it lasts me a month. I draw off gas to a number of instruments at 60 PSI. It's cheaper than a nitrogen generator for the volumes we need. I'm not counting tank rental in the cost.
Click to expand...

Any idea how many cubic feet that 230L amounts to? So you can use the liquid in gas form?
 
Huckster79 said:
Any idea how many cubic feet that 230L amounts to? So you can use the liquid in gas form?
Click to expand...
In reverse order, yes, they have a take-off for the gas. It is the same fitting as for a cylinder. I use the same regulator as for the cylinder- the high-pressure gauge doesn't register, but I regulate the low pressure side to 65 PSI.

230 L gets us about 5600 cubic feet at 1 atm : http://www.airproducts.com/Products...s/weight-and-volume-equivalents/nitrogen.aspx

Note that the 230 L Dewar lasts me about a month whether I use it or not, since the gas is always boiling off and venting. If you don't draw it off fast enough, the safety valve will pop and make a loud hissing noise, it makes everyone jump until you get used to it. A lot of companies with "house nitrogen" piped through the facility use large tanks of LN2 and draw off the gas, just on a larger scale. If I use a cylinder, I can run one mass spectrometer for 2 days if I turn the gas off at night. With the Dewar, I can run a mixture of 5 instruments at once if I needed to so.
 
Well here is my old cowl cover...
IMG_4453.JPG

Here is my new one, that took some hours to sew! It ended up just a bit shorter than I wanted it to, I wanted it to come just shy of the windsheild... IMG_4458.JPG
IMG_4456.JPG
IMG_4455.JPG

Being the Continental it is and always having a little puddle under the vent tube which would be covered by the cowl cover, I sewed in about a 1 foot chunk of old air compressor hose that happens to fit perfectly inside the vent tube, so when I put the cover on I can slide that in there and keep the cover from getting all that oil in it..
IMG_4459.JPG

If I do a lot of cold weather flying next year away from home base I may sew on a 4-6" extension so it can be cinched tighter and "seal" off this open area.
 
Hi,
Just to add a few thoughts here.

I have been building/testing engine dehumidifiers for my planes for several years.

The desiccant systems will work very effectively and for a long time between recharging if designed and installed properly.

I purge the engine in my 185 after each flight. I use a hairdryer with an adapter that fits snugly over the crankcase vent tube. The "COOL" button is held on all the time so as to purge the engine with ever so slightly warm air.
Take the oil filler cap off and run it for 10 min or so after each flight. While that's running I hook up my desiccant system and run it til next flight.
There is a monitor in the return air from the crankcase and it will read usually 8-15% humidity.
It works well and only takes a few moments to hook up.
Tom
 
Tom Hale said:
The desiccant systems will work very effectively and for a long time between recharging if designed and installed properly.
Click to expand...

I still haven't built anything - The big challenge is the lack of a good way to pump air through my engine since the breather comes off the top of the oil filler tube so it's one (tiny) way in, and the same tiny way out.

Sensor technology is improving - There's at least a temp sensor I could drop all the way into the crankcase now, though I'd much rather be measuring the humidity down there too. I'm sure either would preclude getting another tube in there to pump any sort of gas into the engine.

I purge the engine in my 185 after each flight. I use a hairdryer with an adapter that fits snugly over the crankcase vent tube. The "COOL" button is held on all the time so as to purge the engine with ever so slightly warm air.
Take the oil filler cap off and run it for 10 min or so after each flight. While that's running I hook up my desiccant system and run it til next flight.
There is a monitor in the return air from the crankcase and it will read usually 8-15% humidity.
Click to expand...

Interesting, and very cool! Thanks for posting, Tom!
 
The temp/humidity logger I use is a Elitech GPS-6 It will log and plot the temp/humidity with a very tiny probe that I have lowered into the crankcase from the oil filler hole.
They also make a wireless version when wifi is available and a cell version which I have when experimenting with different system setups.
For those interested the aquarium pump versions pump around 1.5-2.0 L/min.
The engine in my C-185 does have a different setup with the oil filler and dipstick and breather all different places. This is the IO-520-D non permould.
 
Tom Hale said:
The temp/humidity logger I use is a Elitech GPS-6 It will log and plot the temp/humidity with a very tiny probe that I have lowered into the crankcase from the oil filler hole.
Click to expand...

Interesting. I've always looked at this from the perspective that I'd rather make my own logger with RasPi/Arduino and then eventually expand it to become part of the control system for the dehumidifier when I build that. However, that GSP-6 is pretty cheap.

Do you have any tricks for ensuring the sensor gets into the crankcase but not into the oil itself?
 
Well yes, with a caveat. On my testbed engine the IO-520 sandcast case. The oil filler neck past the opening is quite large and I use a rubber plumbing cap that comes with a spiral hose clamp.
Make a small hole in the middle and run the probe through the hole about 12-14" and lower it into the case. Its a air tight fit and I can get a good reading.
 
Tom Hale said:
Hi,
Just to add a few thoughts here.

I have been building/testing engine dehumidifiers for my planes for several years.

The desiccant systems will work very effectively and for a long time between recharging if designed and installed properly.

I purge the engine in my 185 after each flight. I use a hairdryer with an adapter that fits snugly over the crankcase vent tube. The "COOL" button is held on all the time so as to purge the engine with ever so slightly warm air.
Take the oil filler cap off and run it for 10 min or so after each flight. While that's running I hook up my desiccant system and run it til next flight.
There is a monitor in the return air from the crankcase and it will read usually 8-15% humidity.
It works well and only takes a few moments to hook up.
Tom
Click to expand...
My system as well. After each flight, I do the same purge using a beach toy inflator as soon as I get the plane in the hangar. This morning I noted that the ambient humidity in my hangar was 64%, the humidity in the dessicant chamber was 12%, and the return (coming from the oil separator) was 15%.
 
What pump are you guys using? I have a big fish tank pump in mine but man by time it pushes out I can hardly feel it...

I’m going to build a purger that’s a good idea! That makes a lot of sense too to just blast the worst of it out.
 
Here's a question for the chemists... What exactly are the combustion byproducts that are harmful to the engine, and how long would one need to purge to get rid of them?

I like all of this purging stuff you guys are doing, but since no matter what I do I'll have very limited flow into the bottom of my engine, I'm thinking about the harmful things besides just moisture and whether it makes sense to do an open-loop or closed-loop system.

I was thinking before that I'd do a combo system: It would start as open-loop and just purge with ambient air, and when the humidity was fairly close to ambient then it'd go to closed-loop with desiccant, which would only need to absorb a limited amount of moisture.

However, I'd also like to ensure that I'm not pumping any harmful gases around in a circle when it gets to closed loop...

I was also thinking that I would be using a tube extending down into the crankcase and pumping dry air into the crankcase and then letting it exhaust around that tube to solve my one-tiny-way-in problem - Essentially, a coaxial setup with a small rigid tube in the center of the current oil filler tube.

However, now I'm also thinking about potential harmful effects on the cylinders if there's a positive pressure differential inside the engine - That means that I'd be spreading any potentially harmful gases inside the engine out through any cylinders whose valves aren't closed. I think I'd rather the leaks allow fresh air in vs. corrosive gases out, so I need the pump to be pulling out of the crankcase instead of pumping in.
 
Hmmm. I'm thinking I could use a pair of these sensors, one inside the oil cap and one outside, to measure performance in several ways:

https://www.adafruit.com/product/3660

They measure temp, humidity, pressure, and VOC gases. It'd be very interesting to just log without venting, and then hook up the pump in an open loop with no desiccant, just pumping in fresh outside air to see what that looks like, and then build the rest of the code and machinery to switch between open and closed loop.
 
Forgot to mention, I saw a new product at Oshkosh this year that seems to be very well done. Expensive at nearly $1000, but pretty much does everything I'd want and doesn't require me to spend time engineering my own:

https://www.rpxtech.com/drybot.html

Made by the same people that do the DynaVibe prop balancer.
 
Checkout_my_Six said:
And....remember there is an intake and exhaust valve that will be open and expose an air passage thru the engine
Click to expand...

Most people leave the pistons in when parking the plane for the winter.:)

Oh dear - that post was years ago. Sorry.
 
You must log in or register to reply here.
Back
Top