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EGT Limitation
Hi,
Due to a very small tubrine, my engine is EGT limited. With increased boost and increasing rpm's (redline is about 8000rpm) egt is the limiting factor, even with reasonable ignition advance, so advancing any further is barely an option to reduce egt's any more. Because the engine is about 8:1cr it's thermal efficiency is also not very high compared to higher cr engines. So i can use water injection to increase my det. threshold to be able to run more boost, but, 100Water and 50/50WM doesn't lower my egt's (some ppl say it should, but i never noticed it during my logs). So do you guy's have any ideas what i can do to keep my EGTs low to be able to run the boost with water/WM i'am able to do det. wise? Thanks in advance |
#2
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Re: EGT Limitation
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#3
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Re: EGT Limitation
the turbine ar is a GT28RS 0.48ar on the T3 turbine housing.
I'am seeing: /wo WM: 898°C @ 8030rpm / 220kPa @ Lambda = 0,769 /w 50/50: 906°C @ 8065rpm / 221kPa @ Lambda = 0,776 950°C is my personal limit, but i would feel a bit better if i can keep it a bit lower then that. Because i know that the material of my exhaust manifold is not rated for that kind of temperatures and i would like to avoid cracking. But up to now it hold's pretty well. Also my goal for this year would be to run more in the region of 12:1 or 12.5:1 if possible afr, but then i would definitly be above 950°C. Also i'am planing for more boost, when i've fixed my ignition misfire issue. What is your EGT limit? I'am injecting 140cc constant 50/50 WM by weight. This gives me a ratio of water to fuel of about 24%@4000rpm/200kPa falling to 8,6%@8000rpm/230kPa. My question to the experienced guy's here: Is there anything with water injection which effects EGT's directly besides the normal "more advance, richer mixture" things which also are valid on a non-WM injected engine? I thought about a second stage (for high rpm) of pure water at the TB or direct port inj. but this makes the setup much more complex and i would avoid any kind of unneccesary complexity. |
#4
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Re: EGT Limitation
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COULD BE SPARK PLUG HEAT RANGE/ BAD FUEL ATOMISATION/TOO MUCH FUEL INJECTED/RETARDED TIMING/IGNITION SYSTEM FAULTY OR OVERHEATING COILS/DWELL TIME INCORRECTLY SET POST SOME PICTURES OF YOUR PLUGS |
#5
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Re: EGT Limitation
Very rich AFRs plus water methanol lead to ignition delay and slow flame propagation speed. It has a similar effect as retarded ignition increasing your EGTs.
Misfires can dramatically increase EGTs as the fuel continues to burn in the manifold. I have no personal experience with EGTs as I do not run a turbocharger. 140cc a minute sound like very little to me. I am peronsonally closer to 600 ml/min on less boost. What HP level do you run? Engine capacity or type? Sounds a bit like a Honda B16 or B18 spinning 8000 rpm on a turbo. Sounds like at least 300HP to me. In this case I'd work with 450 to 500ml/min mix. I like Richard's rule of 1 to 1.5cc/min per HP. Sorry to be of no more help. |
#6
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Re: EGT Limitation
Thanks for your comments. A "misfire" could be the reason. I know my ignition system is not the best for WM right now, i know this, i'am currently working on it this year.
But i don't think this will not change the max. EGT. Concerning the mixture rate, at a constant flow rate, it's normal that the concentration get's lower with rising rpm. Engine is as (i guess) mentioned earlier somewhere here in the forum a B16 with around 370hp. I know the flow rate is below usual levels, but i wanted to start thinks slow because i did not had much luck with higher flow rates in the past. |
#7
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Re: EGT Limitation
The engine is not capable of producing EGTs which are high enough to harm any thing. EGT may also be used to detect abnormal combustion events, including the detonation and pre-ignition. you can see the article in Dissertation writing service UK
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Dissertation writing service UK |
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Re: EGT Limitation
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#9
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Re: EGT Limitation
From:
http://etd.lsu.edu/docs/available/et...Thesis2012.pdf When ignition timing was fixed it was found that exhaust temperature increased with increasing water content as a result of later combustion and less heat lost to the ambient environment. However, applying an ignition timing scheme to achieve maximum torque resulted in a decrease in exhaust temperature as water content increased. This is because of the heat lost to vaporizing additional water in the fuel. Furthermore, it was suggested that the use of hydrous ethanol may allow the use of higher compression ratio devices that would increase the power output of the engine [Brewster et al, 2007]. Makes sense. Water leads to an effective retardation of combustion due to ignition delay and reduced flame propagation speed. You lose power. So you need to add timing and voila, EGTs drop again. |
#10
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Re: EGT Limitation
Thanks for the article rotrex I will try to read it.
I agree with the theory of water injection acting similarly as ignition retard. The same theory applies when you over inject fuel or when weak/cold spark is used. I would love to make a chart one day with different water or W/M mixtures at various flowrates including basefuel ,ignition timing and egts with pictures of the spark plug burn to understand better the theory. |
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