larryb Posted June 10, 2015 Report Posted June 10, 2015 Hello: With the recent discussion on engine humidity and de-humidifiers, I thought I'd share some data I've been collecting over the last 6 months. Like everybody else, I've been concerned with the possibility of engine corrosion. Some research on the internet suggests that the corrosion rate really ramps up over 60%, and is moderatly high between 40% and 60%. Below 40% RH should not be too bad. Since I could not find much real data on what the actual humidity levels are inside an engine, I decided to build a device to measure and log the humidity, and run a few experiments. The measuring device is a Silicon Labs Si7007 with an accuracy of +-5%. I built a probe to insert this in the dipstick of my Lycoming IO360 and suspend it about 1" to 2" above the oil level in the oil pan. The sensor measures both temperature and humidity, and I added a second sensor to measure ambient conditions. The measurements were taken at KRHV, San Jose, CA. The first question I wanted to answer is does it help to remove the oil cap after a flight and let the engine vent. I have also seen the vapor that others report upon opening the cap after flight. My conclusion based on the two typical graphs below is that it makes a small difference to un-cap the engine. However, it doesn't make a big difference. I think the vapor we see leaving the oil cap is actually oil mist, not water vapor. RH values are quite low right after a fllight. The next question I wanted to answer is related to ground running without flying. In this graph, I had taxied from my hanger to the avionics shop for some work, and back a couple days later. I put the probe on when I got back to my hanger. I saw the highest RH readings ever after this experiment, 100%. Once I saw how much the temperature affectedt the RH, I added some logic to use my multi-point engine heater to keep the temperature at a constant 80 degree F. This gives me the lowest engine RH values. You can also see the effect of the heat on my taxi-test graph above. When I saw how high the RH was I turned on the heat. That drove the RH down a bit, but it stayed high till I flew again. My final conclusions are yes, there is an issue with RH inside the engines. Running without flying is clearly bad. And keeping the engine warm is good. It would be interesting to compare a de-humidifer to the engine heater for effectiveness. Larry 7 Quote
DonMuncy Posted June 10, 2015 Report Posted June 10, 2015 Very interesting Larry. Thanks for the effort. I think tests with a dehumidifier would be very helpful. What can we do to help in getting that data. Quote
larryb Posted June 10, 2015 Author Report Posted June 10, 2015 Here is another graph, taken last winter. Note the lower temperatures and higher resultant humidities. Quote
DXB Posted June 10, 2015 Report Posted June 10, 2015 Huh, I always wondered whether that mist after opening the dipstick was actually water vapor or not. If you can prove it's not, its placebo effect on my psyche will be ruined Also, I'm hardly an expert on this, but seems like RH and absolute temperature would have closely related importance? I.e. there's a lot more moisture available in the air to condense on your cam lobe at 90% RH and 90F than at 90% RH and 40F. Also the temperature trend would be a big factor? Rising temps with moist air would deposit a lot more moisture in a cold engine than falling air temps with the engine temp dropping slower. Regardless, I commend the efforts and look forward to data on efficacy of different dehumidification devices. Quote
larryb Posted June 10, 2015 Author Report Posted June 10, 2015 Also, I'm hardly an expert on this, but seems like RH and absolute temperature would have closely related importance? I.e. there's a lot more moisture available in the air to condense on your cam lobe at 90% RH and 90F than at 90% RH and 40F. I think the key issue here is that at the higher temperature, the moisture evaporated in the air and not sitting on the cam lobes. Lets say we start with a fixed amount of water. At low temperatures that water could be condensed on surfaces inside the engine. At higher temperatures, that water will be trapped in the air and not condensed. If the moisture is in the air and not on the metal surface, then it's not available to enable corrosion on steel surfaces. That said, corrosion is not my area of expertise either. I have done some research on the topic and that is what I took away. Quote
Piloto Posted June 10, 2015 Report Posted June 10, 2015 For corrosion issues check with boat owners. Half of the outboard engine is submerged in 100% salt water and cooled with salt water. For corrosion prevention products I go to West Marine stores. Cheaper and more variety than a pilot shop. José 1 Quote
kmyfm20s Posted June 10, 2015 Report Posted June 10, 2015 Thanks for sharing, very interesting! Quote
PTK Posted June 10, 2015 Report Posted June 10, 2015 Good work Larry! Your data seems to agree with Ken Sutton's conclusions. He has data on dehumidifier and heater. http://www.reiffpreheat.com/Article-Sutton.pdf 1 Quote
larryb Posted June 10, 2015 Author Report Posted June 10, 2015 Peter, Thanks for that Sutton article. I had not seen that before. He does have measurements showing that dehydrators do make a difference. Nice that he has a twin, having a single makes it harder to compare my tests since ambient conditions vary between tests. Quote
Alan Fox Posted June 10, 2015 Report Posted June 10, 2015 Jose' , do you think that bolting a boat Zinc on to the block as a sacrificial anode would be worthwhile on one of these?? 2 Quote
PaulB Posted June 10, 2015 Report Posted June 10, 2015 Don, Is your dehumidifier similar to the one shown in the video in the link above? Quote
DonMuncy Posted June 10, 2015 Report Posted June 10, 2015 Paul, If that was directed at me, no, I built my own. Glad to share any details to anyone interested. Don Quote
PaulB Posted June 11, 2015 Report Posted June 11, 2015 Paul, If that was directed at me, no, I built my own. Glad to share any details to anyone interested. Don Yes. I would love to hear about it. I've been contemplating building one myself. Quote
Steve65E-NC Posted June 11, 2015 Report Posted June 11, 2015 Help, please. This seems like a good topic to look for information related a local problem. Our fbo has one large steel communal hanger that was, long ago (maybe 25 years) , just put up on the now un-even ramp slab. Later overlays to the surrounding ramp have left this floor lower and lower. The fbo, without much success, seems to focus on channeling the rain water to a central drain. Puddles of water are left standing under aircraft a week or so after rain. Someone here, in an earlier topic, hinted that this could increase engine corrision. I am looking for arguments and data to convience the fbo to put in a level scab overlay on the existing floor. With solid data I can get other owners to join me if this investment is indicated. Any data, scientific or antedotal appreciated. Quote
Piloto Posted June 11, 2015 Report Posted June 11, 2015 Jose' , do you think that bolting a boat Zinc on to the block as a sacrificial anode would be worthwhile on one of these?? Just clip one of these http://www.westmarine.com/buy/martyr--clamp-on-grouper-anodes--P000485144 to the prop and problem solved. In my younger days I saw a lot of these hanging when I was barnacle cleaning yachts in the water to pay for flying lessons. Hated when someone onboard flushed the toilet. No dump tanks required on those days. José 2 Quote
kmyfm20s Posted June 11, 2015 Report Posted June 11, 2015 Good work Larry! Your data seems to agree with Ken Sutton's conclusions. He has data on dehumidifier and heater.http://www.reiffpreheat.com/Article-Sutton.pdf Great article! 1 Quote
Yetti Posted June 11, 2015 Report Posted June 11, 2015 Jose' , do you think that bolting a boat Zinc on to the block as a sacrificial anode would be worthwhile on one of these?? Cathodic protection-galvanic corrosion Quote
terbang Posted June 11, 2015 Report Posted June 11, 2015 Some time ago I found this on a European GA forum: http://www.euroga.org/forums/maintenance-avionics/2043-engine-dehydrator?page=1 I have built almost exactly what is described there and use it each time I put our plane in the hangar. Quote
Browncbr1 Posted June 11, 2015 Report Posted June 11, 2015 Just clip one of these http://www.westmarine.com/buy/martyr--clamp-on-grouper-anodes--P000485144 to the prop and problem solved. In my younger days I saw a lot of these hanging when I was barnacle cleaning yachts in the water to pay for flying lessons. Hated when someone onboard flushed the toilet. No dump tanks required on those days. José Jose, do you actually use an anode like that? I had never though of using an anode, but do you think it really makes a difference? I will feel like a total idiot if this is all a joke, but if not, I have some old anodes that I can clap to my muffler. . I think the best thing is just fly once a week. Quote
Guitarmaster Posted June 11, 2015 Report Posted June 11, 2015 Just clip one of these http://www.westmarine.com/buy/martyr--clamp-on-grouper-anodes--P000485144 to the prop and problem solved. In my younger days I saw a lot of these hanging when I was barnacle cleaning yachts in the water to pay for flying lessons. Hated when someone onboard flushed the toilet. No dump tanks required on those days. José I have never heard of this until now. It sounds very interesting and makes total sense to me. one question, what is the electrolyte that produces the current? is it simply the humidity in the air? You have to have a path back to the aircraft for the electrons to flow. simply hanging it from the prop or exhaust does not seem to complete the circuit. What am I missing? With as weak an electrolyte as humidity, the material would have to be magnesium to work properly I would think. Since aluminum has -1.1v, zinc has -.6v and mag has -1.6v. It would make sense with an aluminum airplane so you would need to create a negative potential. Anything less it seems you turn the airplane into the anode and you have much bigger problems. Quote
PaulB Posted June 11, 2015 Report Posted June 11, 2015 https://www.sorbentsystems.com/desiccants_types.html This site has an interesting breakdown of different types of desiccants. Makes me wonder if it's worthwhile to find some molecular sieve to get the lowest humidity possible. Quote
Marauder Posted June 11, 2015 Report Posted June 11, 2015 https://www.sorbentsystems.com/desiccants_types.html This site has an interesting breakdown of different types of desiccants. Makes me wonder if it's worthwhile to find some molecular sieve to get the lowest humidity possible. Mole sieve is the stuff you want. Some of the others can outgas some stuff you don't want in your engine. As can some of the indicating moisture dessicants. https://www.deltaadsorbents.com/13x-8x12-molecular-sieve-desiccant-1lb/t101c22p108.aspx?gclid=CKf-34z2h8YCFcE2aQodHisAlQ Quote
N201MKTurbo Posted June 11, 2015 Report Posted June 11, 2015 I believe molecular sieve will adsorbed the oil vapor too. I would stick to silica jell. Quote
larryb Posted June 11, 2015 Author Report Posted June 11, 2015 I don't think a sacrificial anode will work in this case. The corrosion we are talking about is "microcell." Basically a spot of moisture, combined with contaminants on the surface of steel creates a microcell that creates the corrosion. You can't get the sacrifiical anode involved in that cell. A boat is different since it is floating in the electrolyte. Corrosion on a boat engine is not microcell. This is, however, why galvanized steel works. Here you have the sacrifical anode coating the entire surface. And even if it gets scratched and exposes the steel underneath, you have the tin very close by to be sacrificed. Outgassing of desiccant has been a concern for me. I've had a case where dessicant on a boat caused corrosion on some metal it came in contact with. That's one reason I have stayed away from a desiccant dryer. Larry Quote
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