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 Post Posted: Sun Jan 22, 2012 8:12 am 
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ditto. what Webermaniac wrote. All of your explanations have been very helpful.

Mark, Shrinker, so let me undertand this - at part throttle in most instances carb (or FI) is set up to deliver a leaner AFR because the load is signifcantly lower. If the timing is not ideal to match those conditions (slower burn), the same phenomenon occurs - too much CO2 (and NOx ?) and the end result is additional throttle must be added to hold the load.


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 Post Posted: Sun Jan 22, 2012 4:42 pm 
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I dont know quite exactly what you asked as it seems confusing or maybe typoed.
Part throttle running or more correctly less than maximum load percentage running is usually described in text books (and its described in Obert and Larew ) as being not necessary to run the mixture at Lambda 0.87. So you can opt for fuel economy instead.
It is claimed by researchers that the lower cylinder pressures associated with lower power production can tolerate leaner mixture without engine damage. That is the case for small cam motors and stock compressions. That isn't the case for hotrods. The discrepancy is usually attributed to valve timing. The exhaust contamination as a percentage of the charge mass when running at part throttle cruise is higher than at WOT so the flame speed is reduced. The timing for low load has to be advanced compared to high load to compensate for the slower flame speed of the leaner mixture and the exhaust contamination. There is a problem with the researchers and thats that they do they work on low power per cubic inch engines. That point of exhaust contamination relative to the power output is not the same for hotrod engines. It can be anywhere depending upon the combination and whats wrong with it. Ive seen bad engines that cannot run anymore than 50hp without having to go to lambda 0.85 or richer to avoid very high NOx damaging the engine. Some people build really bad engine combination's, there not predictable. Forget about fiddling with ignition timing to stop the NOx, these engine are just terrible they loose power if timing is reduced but cant control the peak temp so there junk.

When a burn is close to stoich but on the rich side, less timing produces an increase in wasted HC, excessive CO and unused O2. It doesnt produce NOx or high CO2. Some hotrod engines dont follow that exactly, bad engines you have to flood them to pull the NOx down. Poring fuel into an engine eventually gets it to a point of using the O2's early enough so it cant make high peak pressures and start burning things. Its the Hydrogens that suckup most of the O2 supply, depending upon the fuel mix in your country about 58% of the fuel is hydrogen, that reacts first and makes water, its that water reaction that consumes heaps of Oxygen and the richer you get the more water is made making it harder for the CO and CO2 and NOx to form later in the combustion event. You just simply run out of O2's. When its really rich there is an increased number of unused Hydrogens exiting the exhaust and the WB cell reacts them. Gas benches dont see H's WB's do so as soon as you go really rich and get a hot of H's the cell reaction loading goes up heaps and the WB reports back a far richer mixture than truth. This is why you need to keep track of jetting changes, if the jetting should have richened it 12% but the WB says it got 16% richer then you can surmise that you just blew some H's out the exhaust. Cross check it with a gas bench and the gas bench will reveal the correct 12% jetting change. Funny huh.


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 Post Posted: Sun Jan 22, 2012 6:16 pm 
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Mattax wrote:
If the timing is not ideal to match those conditions (slower burn), the same phenomenon occurs - too much CO2 (and NOx ?) and the end result is additional throttle must be added to hold the load.
To get that situation you have to be too much timing, thats what is confusing me about your post. To get too much CO2 is not a bad thing, it has to be at the sacrifice of CO so thats all good. Its how to control the NOx when your getting maximum possible CO2 and zero CO thats the problem. For part throttle cruising you dont need maximum power mixtures you just need maximum fuel economy mixtures without the generation of NOx. If you tune a hotrod so that its too lean at cruise and it makes NOx when you stomp on the throttle the first few events of the cylinder will be too hot and maybe damage will occur.
This is how it works, CO2 is formed when the temperature of the chamber is near the top that the components will handle, The more CO2 made the less CO will be made, the more CO2 made the more radiant heat in the chamber. This radiant heat heats up the Nitrogen in the atmosphere it reacts with the O's and forms N2O and some other N and O combination's for a very short period of time. N2O is nitrous oxide. That then breaks down into NO. The reaction of that sucks up energy so the temperature of the chamber stabilizes at the formation of NO. The term NOx refers to all gases that are combination's of N and O. Some Nitrogens are present in fuel (because it's organic stock) and the gov tries to get them to remove it but they cant get it all so some of the NO is formed from Fuel nitrogen. That reaction is not severe like the atmospheric nitrogen one. It just creates NOx which is a pollutant (acid rain) but its doesnt cause as much damage to the engines. Under all situations if NOx is made the temperature is too high for components to be safe. NOx is always made in the arc so there is always some small amounts of it in the exhaust. When NOx is made in the arc but the rest of the burn is not hot enough to make NOx the arc NOx will remain because it takes a few degrees more to break it down than what it takes to make it so the cold burn cant do that, so it remains. As long as the NOx is not made against the surface of a part the engine will survive. NOx is the precursor of detonation.
If we look at a temperature line and spot the reactions of gases it goes like this.
Low temp - Hydrogen into water - 60% of the atoms in the fuel suck up 30% of the oxygen's. This generates the energy to fast react the carbon.
moderate temp, around 1800F carbon reacts to make CO.
high temp, around 2200F carbon monoxide (CO)reacts to make CO2.
excessive temp around 2800F Nitrogen reacts with available O's
Superhigh temps around 2900F NOx breaks down into seperated N and O;s again. NOW you got some really hot O's looking for something to do., so they go and attack a piston, bye bye piston. The water also breaks apart and you get hot H's and hot o2 from that, so plenty of hot Os to go around destroying things.
Then the O supply runs out and NO is formed and the reacts stop and stabilise the temp.


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 Post Posted: Tue Jan 24, 2012 2:34 am 
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Shrinker, ive been going back over some of what you posted in relation to compression and heat required to burn and combustion efficiency. Could you please expand on this as i will be running O2's and EGT's, especially about the temp reduction.

Quote:
Ahh I see, the problem with just that equipment is you dont truly know the combustion efficiency, but you can get an idea by using the EGT. You need to create an Excel program that cross references the EGT to the AFR. Or apparently that can be done in logworks with a math channel or something like that its called. never played around with that part of logworks myself yet.
If you increase combustion efficiency with a design change, for instance like adjusting to different tappet clearance, the EGT will go down at the same timing and AFR. Any time EGT goes down with same AFR then you have increased energy conversion to the crank. As the energy from the burn is converted to torque the temperature of the gases in the chamber is reduced, so lower EGT is more energy conversion provided its done at the same AFR. Is that answer your after?


Thanks

Hysteric


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 Post Posted: Tue Jan 24, 2012 3:11 am 
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Umm I dont know what you want to know. What I said in your quote is pretty much it.
EGT is a measure of the wasted energy ,its not a measure of the AFR. You can have a higher temperature EGT with the same AFR if you have done something that reduces the efficiency of the energy conversions. The whole purpose of an engine is to convert chemical energy into torque, if you dont do that as well then there will be more wasted energy. You have to have a gas bench to properly do it because you can have situation where the AFR is equal from one test scenario to the next but less Fuel and oxygen are utilised so the temperature could be anything. EGT is not what everyone thinks it is.


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 Post Posted: Tue Jan 24, 2012 3:47 am 
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I would have thought that an increase in combustion efficiency would create more heat......what am i missing?

Hysteric


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 Post Posted: Tue Jan 24, 2012 4:18 am 
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Your missing how energy is converted. Pressure is converted to torque so energy is transferred from the combustion chamber to the crankshaft. That reduces the energy contained within the combustion chamber so we measure a reduced heat.
Its all about energy. they dont teach it plain and simple enough in schools. Energy is a parcel that can be moved around the place. When there is lots of them in one place we can measure them as a pressure or a force or a heat etc. All energy degrades to the form of heat. Heat is the lowest form of energy so when we measure heat we are measuring the remains of what is wasted and not converted to higher forms like kinetic energy or pressure etc.
Imagine this. We have a theoretical engine that is revolving at very slow speed maybe with a really long stroke, it's going so slowly in fact that it can push on the piston for such a long time that the pressure in the chamber is converted to atmosphere. All the energy from the burn would be converted to force. The EGT would be nothing.

Whats confusing is when we lean the AFR the EGT goes up. Thats because we are just talking about the EGT and not considering how much energy is released inside the chamber. When the mixture is leaner the burn is more efficient creating more energy per unit of fuel and Air consumed. the EGT is higher but its a lower percentage of the peak temperature of the chamber. In other words teh chamber temp goes up more than what the EGT does.
We dont measure the peak temp in the chamber we just measure the wasted energy thats in the Exhaust. We need a gas bench to "see" the temperatures achieved in the chamber. With a gas bench you can see the conversions, you can see the NOx, you can see the carbon gas ratios, all these things tell the skilled observer the efficiency of the burn. Albeit as an average because a gas bench is not an instantaneous tool.


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 Post Posted: Tue Jan 24, 2012 4:43 am 
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shrinker wrote:
You can have a higher temperature EGT with the same AFR if you have done something that reduces the efficiency of the energy conversions.

Thats the critical point. If your doing engine development and changing parts you have to keep the AFR constant and then you can see changes in EGT that will correlate with combustion efficiency or energy conversion. If the combustion efficiency goes up the EGT will go up but if the energy conversion gets better the EGT will go down, what is the outcome depends on the severity or the effectiveness of what you have done. EGT is not simple.

Consider this. You lean the jetting a little so its less rich and the EGT goes down, well you may have just improved combustion efficiency and that has resulted in more energy going to the crank so the engine may be more powerful. BUT you need a gas bench to find out if you still have full utilization of the Oxygen. It may be that you have leaned it and a poor area of the chamber has been less able to complete combustion so that would be a reduction of chamber energy and a reduction of energy to the crank resulting in less power. See its not a simple thing.
The EGT is a measure of waste but you have to know how much your using to figure out the percentage of waste.


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 Post Posted: Tue Jan 24, 2012 9:14 pm 
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Shrinker, Yes I typoed the CO2 instead of CO in my question but I think you did better than answering what I was trying to ask! Also, thanks for explaining how the Nitrogen relates to the combustion process. Is it then correct that going on the lean side of stoich we don't see CO, but do see more NOx in the exhaust primarily because the combustion temperatures are high?

PS. Some fuel companies here were advertizing Nitrogen enhanced fuel this past year or so.


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 Post Posted: Wed Jan 25, 2012 5:36 am 
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On the lean side of stoich there is hardly any CO. A good burn at leaner than stoich will come up with very close to zero CO.
The NOx may or may not be there it depends on the pressure of the chamber (which is actually power production isnt it). There is also the situation where you can go so lean that there is little heat produced so even the NOx disappears.
I dont know why they would advertise nitrogen enhancement. The presence of Nitrogen in the fuel is the easiest way to fail an emission test. It also contributes nothing to power so I see no sense in it.


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 Post Posted: Wed Jan 25, 2012 8:19 am 
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shrinker wrote:
On the lean side of stoich there is hardly any CO. A good burn at leaner than stoich will come up with very close to zero CO.

And if the burn is incomplete or cold, the CO will form anyway, yes?

Re: Nitrogenated' Fuels. Sorry, my eyes glaze over when I read the PR 'nitrogenated' Press Release
and other marketing hype. But from a report in the pretty respectible Scientific American
apparently its in the detergent additive.
http://www.scientificamerican.com/artic ... riched-gas


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 Post Posted: Wed Jan 25, 2012 12:37 pm 
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Mattax wrote:
And if the burn is incomplete or cold, the CO will form anyway, yes?
Yes thats correct. The most useful way to track efficiency of a chamber design is to track the O's. If you have CO at stoich then you will most likely have O's. If you have chamber areas where the burn doesnt proceed, some may call that a 'dead area', you will have HC and O, areas that are partial burns will have CO and O.


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