skydvrboy Posted February 18, 2019 Report Posted February 18, 2019 Is there a CHT temperature that you shouldn't go below? I've tried searching and haven't found any answers. The reason I ask, when I was tootling around on a cold day recently at 1,000' AGL and 120 mph, the CHT gauge was pegged at 200o. I had the RPM backed down to 2400, the MP around 20", and the mix nob just in far enough to run smooth. With that low power setting, she just wasn't generating much heat. Oil temps were just barely in the green (low side), but is it OK to run with CHT's that low? Quote
ArtVandelay Posted February 18, 2019 Report Posted February 18, 2019 The scavenging agent creates lead bromide requires high combustion temperatures, shell white paper recommendation is 1000-1200 RPMs, lower will result in lead fouling. I don’t think cylinder temperature would matter much. Tom Quote
rbridges Posted February 18, 2019 Report Posted February 18, 2019 https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/techart-18-30071600.html Quote
Shadrach Posted February 19, 2019 Report Posted February 19, 2019 Doing that for a little while probably isn’t going to cause any problems. Extended operations running CHT’s in the low 200s could certainly contribute to plug fouling. my question is why run that way? Just lean enough to run smooth in an injected Lyc does not yield best BFSC and does not generate desirable oil and cylinder temps. What’s the benefit? Quote
skydvrboy Posted February 19, 2019 Author Report Posted February 19, 2019 4 hours ago, Shadrach said: Doing that for a little while probably isn’t going to cause any problems. Extended operations running CHT’s in the low 200s could certainly contribute to plug fouling. my question is why run that way? Just lean enough to run smooth in an injected Lyc does not yield best BFSC and does not generate desirable oil and cylinder temps. What’s the benefit? Low fuel flow, why does anyone run aggressively LOP. I've been able to run less than 6 GPH (block) with those low power settings when sightseeing. I didn't lean "just enough to run smooth" though. I leaned until it ran rough and then pushed it back in just enough to run smooth. By my single EGT gauge, I was at least 100-125 LOP. 6 hours ago, rbridges said: https://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/technical-talk/techart-18-30071600.html Based on that article, I would surmise that if 1800 RPM with the prop on the stop during a run up is enough to prevent fouling, then ANY power setting capable of sustaining level flight would produce more than enough heat to burn off any deposits. Am I missing something? Quote
MikeOH Posted February 19, 2019 Report Posted February 19, 2019 43 minutes ago, skydvrboy said: Based on that article, I would surmise that if 1800 RPM with the prop on the stop during a run up is enough to prevent fouling, then ANY power setting capable of sustaining level flight would produce more than enough heat to burn off any deposits. Am I missing something? Possibly that there is more cooling when traveling through the air at over 100 mph than a ground run-up? Quote
Shadrach Posted February 19, 2019 Report Posted February 19, 2019 (edited) On 2/18/2019 at 11:55 PM, skydvrboy said: Low fuel flow, why does anyone run aggressively LOP. I've been able to run less than 6 GPH (block) with those low power settings when sightseeing. I didn't lean "just enough to run smooth" though. I leaned until it ran rough and then pushed it back in just enough to run smooth. By my single EGT gauge, I was at least 100-125 LOP. Based on that article, I would surmise that if 1800 RPM with the prop on the stop during a run up is enough to prevent fouling, then ANY power setting capable of sustaining level flight would produce more than enough heat to burn off any deposits. Am I missing something? One runs agreesively LOP (subjective term) at high power settings because it produces healthy engine temps, cleaner combustion and yields best BSFC (max hp per gallon). I run this way at 1000-2000msl WOTRAO. 50-60LOP is plenty even though the engine will run well much leaner. The previously mentioned benefits diminish at low power settings. At low power BSFC starts to climb again around 20LOP. The combustion event gets so slow that peak cylinder pressure occurs way after the ideal crank position. This means less of the combustion event is converted to mechanical energy. Really well balanced engines see a second EGT peak just as or right before roughness as the combustion event is still in process during the exhaust stroke. You’d be better off running lower MP and setting mixture closer to peak. You’d likely get the same speed but on slightly less gas without running such cool CHTs that you risk fouling plugs. Likely will produce healthier oil temps as well. Edited February 20, 2019 by Shadrach 1 Quote
Shadrach Posted February 19, 2019 Report Posted February 19, 2019 (edited) 32 minutes ago, bluehighwayflyer said: All true. Directly to your question about minimum temps, though, Lycoming says that anything over 150 dF CHT and 165 dF oil temp is ok. There is some bad but mostly very good information in the book of Lycoming Key Reprints linked and screen captured below. Jim http://www.alfako.be/SAFETY DOCS/lycoming---flyer_key_reprints.pdf Thanks Jim. It’s interesting to note that Lycoming minimums are not very realistic and sort of contradictory. Can you imagine any practical scenario where an engine with CHTs in the mid 100s producing an oil temp anywhere near 165? Mike Busch says the following about low CHTs: You caution against excessive CHTs, but is it possible for CHTs to be too cold? Yes, it's possible to run CHTs so cold that the tetraethyl lead (TEL) in the 100LL is not properly scavenged and starts creating metallic lead deposits in the combustion chamber and lead-fouling the spark plugs. However, in most engines, it takes verycool CHTs (down in the mid-200s °F or lower) for an extended period of time (hours) for this to cause a problem. We usually see this problem in airplanes used for fish spotting, pipeline patrol, search and rescue, and other "loiter-mode" operations. Unless you fly at very low power settings (e.g., 50 percent) and/or at very high altitudes and very cold OATs (e.g., FL240 and -30°C), it's not usually a problem. Edited February 19, 2019 by Shadrach 2 Quote
aviatoreb Posted February 19, 2019 Report Posted February 19, 2019 This is a good topic and has come up several times in the past, most recently earlier this year. note my entry was regarding safety to the pilot vs operations of the engine, which of course is an issue too. 1 Quote
carusoam Posted February 19, 2019 Report Posted February 19, 2019 So in this thread... 1) CHT specific... 2) Lead issue becomes a challenge at lower CHTs... an IO550 can easily cruise at 10k’ showing 280°F CHTs a few °F LOP 3) Concerns about piston clearance are raised... Lycoming says 150°F is good. 4) CHT isn’t an exact reading for lead ball production. It’s just the best we have... 5) How LOP can you go? And why would you go there....? The advantages of going LOP... Converts all the gasoline to power... Keeps EGTs And CHTs under control. Disadvantages of going LOP... Without a decent engine monitor, it gets challenging... Power drops off quickly, the more LOP you go... Thermodynamic efficiency is dropping the more LOP you go... Down low, a well fuel balanced (tight gami) IO550 can get 90°F LOP before the fuel fails to light.... the engine just stops producing any power... like pulling the mixture to ICO, except the fuel is still flowing towards the exhaust pipe... At 10k’ of altitude, the same engine has difficulty getting 50°F LOP before the fuel fails to light... Tell me more about how you get 100 - 125 °F LOP? We May be accidently going to an extreme... we went from max power and efficiency available to something else... 1) with cold CHTs we don’t need to go past peak to have temp control... it’s cold already... 2) We like WOT because it improves the efficiency of mixing, and the flow of the engine’s intake.... 3) Going deep LOP limits power available, and stinks for efficiency.... If max power and efficiency aren’t desired.... Select a lower MP... Choose a mixture closer to peak... Sounds like.... If a little LOP is good... then a lot LOP must be better....? Unfortunately, just not so... PP thoughts only, not a thermodynamics guy... Best regards, -a- 1 Quote
skydvrboy Posted February 19, 2019 Author Report Posted February 19, 2019 16 minutes ago, carusoam said: Tell me more about how you get 100 - 125 °F LOP? I don't know. I have a single probe Alcor EGT and am assuming each tick mark is 25 degrees. I start leaning it slowly and watch for it to peak. I kept leaning it until it ran rough (approximately 125 below where it peaked). Then, I added a bit more mix until it smoothed out, ended up about 100 below where it peaked. I have been able to duplicate this at high power settings, but this time I wanted to go slow. I don't typically run it that lean because as I keep moving the nob in slowly, you can hear the power increase as the gauge moves toward it's peak. Thus I typically run closer to 25-50 LOP. I have the IO-360 instead of the IO-550 if that makes a difference. The Shell article above only mentioned 200-250 C, but, if I read it correctly, was referring to combustion temperatures, not CHT's. Per Mike Bush's comments, that is exactly how I was running my engine, low power "loitering" for 2 hours. Fortunately, it is not how I run it normally, so it would seem any deposit should burn off rather than build up. After reading all these comments, it seems like I wasn't going to do any harm to the engine on a 2 hour flight. However, I could have ran it more efficiently by running it at or very close to peak EGT since my power setting was at approximately 55%. 1 Quote
Shadrach Posted February 19, 2019 Report Posted February 19, 2019 (edited) 21 hours ago, skydvrboy said: I don't know. I have a single probe Alcor EGT and am assuming each tick mark is 25 degrees. I start leaning it slowly and watch for it to peak. I kept leaning it until it ran rough (approximately 125 below where it peaked). Then, I added a bit more mix until it smoothed out, ended up about 100 below where it peaked. I have been able to duplicate this at high power settings, but this time I wanted to go slow. I don't typically run it that lean because as I keep moving the nob in slowly, you can hear the power increase as the gauge moves toward it's peak. Thus I typically run closer to 25-50 LOP. I have the IO-360 instead of the IO-550 if that makes a difference. The Shell article above only mentioned 200-250 C, but, if I read it correctly, was referring to combustion temperatures, not CHT's. Per Mike Bush's comments, that is exactly how I was running my engine, low power "loitering" for 2 hours. Fortunately, it is not how I run it normally, so it would seem any deposit should burn off rather than build up. After reading all these comments, it seems like I wasn't going to do any harm to the engine on a 2 hour flight. However, I could have ran it more efficiently by running it at or very close to peak EGT since my power setting was at approximately 55%. You're not going to hurt anything running that way. As I said earlier, there is potential for plug fowling. The only other issue I see is that your using a single probe EGT. That means your using that cylinder (likely #3) as a proxy for all four. While not ideal, I would surmise that your engine's spread is close enough to do it safely given that it runs 125 LOP at low power (to run that far LOP at low power requires very consistent F/A ratios form cylinder to cylinder). That being said, you really want to lean on your richest cylinder when LOP (ensuring the rest are leaner) and on the leanest when leaning ROP (ensuring the rest are richer). You're lucky to have a conforming engine that runs smoothly across the mixture spectrum but that is not a substitute for real data. Also, the 200-250C reference is to plug temperature in the cylinder not combustion temp (which is way hotter at any usable mixture setting). If the plug is below the phase change temp of Lead Bromide, the plug will collect Lead. Edited February 20, 2019 by Shadrach 1 Quote
skydvrboy Posted February 19, 2019 Author Report Posted February 19, 2019 3 minutes ago, Shadrach said: Also, the 200-250C reference is to plug temperature in the cylinder not combustion temp (which is way hotter at any usable mixture setting). If the plug is below the phase change temp of Lead Bromide, the plug will collect Lead. Thanks for clearing that up. 3 minutes ago, Shadrach said: You're lucky to have a conforming engine that runs smoothly across the mixture spectrum but that is not a substitute for real data. I couldn't agree more. I've been talking with my non-flying financial partner about adding an EDM. The decision to add one has been made, which one is still up in the air, but I suspect a JPI 900 will get added this year. For now though, I have been running a bit leaner than I'd like and keeping %HP down to be on the safe side. Quote
Shadrach Posted February 19, 2019 Report Posted February 19, 2019 1 minute ago, skydvrboy said: Thanks for clearing that up. I couldn't agree more. I've been talking with my non-flying financial partner about adding an EDM. The decision to add one has been made, which one is still up in the air, but I suspect a JPI 900 will get added this year. For now though, I have been running a bit leaner than I'd like and keeping %HP down to be on the safe side. Good deal. I am not one of those folks that believes you need an engine monitor to run LOP safely. You're equally in the dark on either side of the mixture spectrum without one. That means it's prudent to run conservatively rich or conservatively lean. The up shot of running conservatively lean is that in the off chance you have an injector issue , you'll feel the engine get rough and it won't put your mixture in a bad place on that cylinder. Quote
carusoam Posted February 19, 2019 Report Posted February 19, 2019 Single EGT, with increments of 25°F, is way better than no EGT at all... Having a tight gami spread is best for uniform leaning. EGT raw numbers are relative to a few things including probe placement... Degrees relative to peak... How deep LOP one can expect to get, MAY also be in that relative area... +1 when the financial administrator gives the green light for an engine monitor... go with it! It is impossible to know your gami spread without one. Problem solving gets 100 times easier with one... A well balanced gami spread, first and last to peak... occurs at the same FF, or within 0.1 gph... some engine intake designs work better than others... the Mooney IO550s get a really nicely balanced intake system... the IO360s are really naturally good too... the O360 is challenged by the carb not being as adjustable as four individual injectors... The IO540 is challenged by its non-curvy log style air intake... Best regards, -a- Quote
Hammbone Posted May 21, 2019 Report Posted May 21, 2019 My guess is you are using original gauges. If so they can't be trusted any farther than you can kick an anvil. 300 deg. is getting low. You said the gauge was 200 which is pegged low. Very suspicious. Plus your oil temperature should be up to 180 after 15 to 20 min of flight at pretty much any power. Again gauge in accuracy.(Unless your therm. valve is stuck open) Quote
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