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More About Leaning During Climb
"John" wrote: So, what is magic about the 1350 degree sea-level full rich takeoff temp? Can anyone suggest any good reasons why it is not equally safe to lean to operate at the 1450 degree conditon during climb? The EGT isn't what matters; it's the CHT's that are important. As long as they don't get too high, go ahead and lean as you climb. I have an engine analyzer that I watch while I climb, using whatever mixture setting I need to keep the hottest cylinder below 400 deg, F. If 1450 degrees is good for hours and hours of continuous operation at cruise, and if cylinder temps are green, why needlessly expend more scarce fossil fuel operating at 1350 degrees? No reason at all, IMO. Won't the engine also develop more power at 1450 degrees than at 1350, which seems quite worthwhile for a number of reasons? Yep. I'm not trying to be contentious, just wondering if anyone has ideas about it that I haven't considered. I think you've got it covered. -- Dan C172RG at BFM |
#3
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Thomas Borchert wrote in
: That first part of your sentence is something I have NEVER heard of before. Any source on that? Anyone here work with water injection internal combustion engines? [Hey, I round web sites which claim up to 60% more power, with no increase in fuel flow. But I didn't rush out to give them my credit card number! G] And for the latter part: The excess fuel isn't doing any cooling per se, it is slowing down the burning process, which leads to that process being cooler. Quite correct, but there is also a substantial heat of vaporization. Also, 100 ROP is probably a bad point to be because it is the point of maximum pressure load during the burning process. A little richer (like 150) would be better. True. But "better" is probably open to interpretation however. 100 ROP gives best power, which also produces the highest peak pressure load - exactly as you say. Is 150 ROP better? Well, the loads are less, and so are the temperatures, but so is the power. Less efficient, wastes more fuel, more pollutants in the exhaust. A much better solution is to produce the same power but well LOP (assuming your engine is balanced for it). The pressure wave integrates to the same effective area under the curve, but the peak is not only lower but less sharp in form. At the same time the fuel usage is at maximum efficiency, and the exhaust is cleanest - not only from a pollution standpoint, but also from the point of reducing any chance of carbon monoxide risks. Back to the first two points... anyone who tunes race engines for a living or some such, want to weight in with more information. Wouldn't be the first time I'm all wet. G ----------------------------------------------- James M. Knox TriSoft ph 512-385-0316 1109-A Shady Lane fax 512-366-4331 Austin, Tx 78721 ----------------------------------------------- |
#4
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James M. Knox wrote:
: A much better solution is to produce the same power but well LOP : (assuming your engine is balanced for it). The pressure wave integrates : to the same effective area under the curve, but the peak is not only : lower but less sharp in form. At the same time the fuel usage is at : maximum efficiency, and the exhaust is cleanest - not only from a : pollution standpoint, but also from the point of reducing any chance of : carbon monoxide risks. I feel obligated to throw in a tidbit here. Having worked on hybrid electric vehicles in a former life, I've run into some interesting engineering tradeoffs in cars. While it's true that running LOP reduces CO emissions, it *increases* NOx emissions. With the higher EGTs and excess O2 running LOP, more of the O2 react with N2 in the mixture to create NOx's. For cars, the EPA says that's bad too. So, fuel injected, O2-sensored cars with catalytic converters have a balancing act between running at peak efficiency, and having to scrub out NOx, or running richer and burning out excess HC's. Fortunately, we don't have to put cats on our planes yet, and NOx is less deadly than CO in flight. : Back to the first two points... anyone who tunes race engines for a : living or some such, want to weight in with more information. Wouldn't : be the first time I'm all wet. G Usually the racer-performance types are all about the horsepower, so talking efficiency is generally useless. They run whatever mixture will maximize HP, nevermind the eye-tearingly rich mixture the exhaust leaves behind! -Cory -- ************************************************** *********************** * The prime directive of Linux: * * - learn what you don't know, * * - teach what you do. * * (Just my 20 USm$) * ************************************************** *********************** |
#5
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"Mike Rapoport" writes:
Because when cars run ROP they only run slightly rich. Then their EGTs would be higher, wouldn't they (assuming that the "P" still stands for peak EGT)? All the best, David -- David Megginson, , http://www.megginson.com/ |
#6
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wrote in message ... While it's true that running LOP reduces CO emissions, it *increases* NOx emissions. With the higher EGTs and excess O2 running LOP, more of the O2 react with N2 in the mixture to create NOx's. Higher EGTs? 50 deg LOP is same EGT as 50 deg ROP. Stan |
#7
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Stan Prevost wrote:
: wrote in message : ... : While it's true that running LOP reduces : CO emissions, it *increases* NOx emissions. With the higher EGTs and : excess O2 running LOP, more of the O2 react with N2 in the mixture to : create NOx's. : Higher EGTs? 50 deg LOP is same EGT as 50 deg ROP. Higher EGT's than running rich. Yes, 50 ROP is the same as 50 LOP by definition, but when rich, there's no more O2 to react and make NOx. I was actually referring to peak vs. ROP with regards to EGT, but it doesn't matter all that much. 1450 or 1500 isn't much difference, as they're both hot as hell. It'll make the exhaust stack glow a nice orange, unless it gets enough air cooling. In any event, it's the excess of O2 with high EGT's (close to stoichiometric burn) that'll make lots of NOx. With all that O2, most of the CO will be CO2 instead. -Cory -- ************************************************** *********************** * The prime directive of Linux: * * - learn what you don't know, * * - teach what you do. * * (Just my 20 USm$) * ************************************************** *********************** |
#8
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David Megginson wrote in
: That's interesting information -- I've often wondered why car engines don't run LOP to cut down CO emissions. Why would the EGTs be higher LOP than ROP, though? Actually, I believe most modern automobiles with electronic ignitions run substantially LOP in cruise. And the EGT's may well be cooler than when ROP - that's just a question of *how* LOP they are running. Slightly different issue: Catalytic converters and exhaust gas sensors potentially could have their place in piston aircraft (I am *not* making a pitch for the converters, but the exhaust gas sensor would provide very useful information). Unfortunately, the life of either, in the presence of unleaded gas being used, is essentially zero. {:( ----------------------------------------------- James M. Knox TriSoft ph 512-385-0316 1109-A Shady Lane fax 512-366-4331 Austin, Tx 78721 ----------------------------------------------- |
#9
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"Mike Rapoport" wrote in news:behdld$nn0$1
@slb6.atl.mindspring.net: Vaporizing excess fuel (or water) lowers cylinder preasure, it does not raise it. Okay... why? Agreed that each GMW vaporized will absorb some heat, and lower temperatures (for a given trapped gas) reduces pressure, but each GMW that is vaporized also represents a substantial increase in either pressure or volume. So again, why? [I'm perfectly happy to be wrong, but what you say would seem to go against every chemistry and physics class I've had over half a century. [Okay, some of the teachers probably weren't very good, but I think the basic physical laws are still true. G] ----------------------------------------------- James M. Knox TriSoft ph 512-385-0316 1109-A Shady Lane fax 512-366-4331 Austin, Tx 78721 ----------------------------------------------- |
#10
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Mike Rapoport wrote:
: If you inject water into an engine with no other changes, power will go down : a lot. I have used water injection to get a high compression engine to run : on 92 octane fuel and the H2O decreases performance. Now if it were a : turbocharged engine, I could increase the MP without detonation and produce : more power, but that power would be the result of burning more air and fuel : (not the water). This could also be due to the poor ignition timing after this is done. The timing (24 BTDC typical) will put the peak pressure pulse after TDC. If you effectively retard this by slowing the burn with water injection, the power will go down appropriately. : Like you said, you are consuming energy to heat and vaporize the excess : liquid. The energy used to heat the liquid to the boiling point and then : effect a phase change is lost. You are puting liquid into an engine and : having it come out the exhaust at a higher energy level (hotter and : vaporized). That energy came from somewhere. It came from the power output : of the engine. Perhaps somewhat, but remember that typically almost 70% of the energy in the fuel for a gasoline engine is *not* used to turn the crank, but rather just makes your muffler glow a nice cherry red. It's the integral of pressure, area, and crank throw that produces rotational energy in the form of torque and RPM. I believe that water injection is pretty much like high octane fuel. Some people (idiots, mostly) believe that by putting fuel in their car that's higher octane than the car's manual stipulates results in increased performance. All higher octane does is let *OTHER* changes that can then be done (advanced timing, increased CR, etc) to increase the power be performed and not damage the engine. Water injection should amount to the same... all other things equal, it will reduce the power somewhat. BUT if you do it, you can then increase the CR, advance the timing, etc... and get more back out of it. Imagine this: inject water into a high compression : cylender and rotate the crank. The water will vaporize into steam. If what : you are suggesting (that the steam is higher in volume and will drive the : piston) where true, you could make an engine that would produce power and : steam from water alone. Man... if only I could get my carb set right for that.... : Try this: Lean to best power mixture in your airplane, note your speed or : climb rate then go full rich and watch the performance decline. Oh yeah... here in SW VA at 2100' field elevation, it about vibrates off its mounts if you takeoff full rich on a 4200' DA day. Doesn't climb too well either. Too rich is bad for everything except CHT's. -Cory -- ************************************************** *********************** * The prime directive of Linux: * * - learn what you don't know, * * - teach what you do. * * (Just my 20 USm$) * ************************************************** *********************** |
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