Re: Staggered H2O/Meth injection
Quote:
Originally Posted by
wallace
If you lower the air inlet temperature with the same inlet pressure the air on the discharge will correspondingly drop in temp. The compressor efficiency is fixed by the physical design. The lowered discharge temperature means a denser charge for the same boost pressure taking away the amount of oxygen displaced by the fluid would give you the increase in oxygen. I pasted a link that has the formula for this as well as some other info.
http://www.gnttype.org/techarea/turbo/turboflow.html
Since I don't think we are using boost terminology correctly to describe the effects of alcohol injection:
When it comes to reaching full boost faster (boost threshold) I would say its simply denser air at the same compressor rpm creating more exhaust energy. Maybe on the onset of boost there is a slight lag but the idea would be that you overcome that slowdown or at least balance out. Boost response, what spool/lag really means, could be slower or probably the same if you are already in the rpm range where the turbo should be near lag free.
A lotta people talk about maximum compressor efficiency and staying in the island but almost nobody does it. We regularly see people on various platforms slapping recirculating compressor covers onto turbos when they chose a surging turbo (which not only lets you get away with being out of the proper map but distorts the map lowering efficiency across the board). We also see people running turbos that can't provide the flow needed at the demanded boost pressure. Since that seems to be how most people do things I don't see these imperfect situations as a reason not to bother with alky until the basics are fixed.... Let the people who choose a correct turbo enjoy the benefits of that while everyone enjoys the alcohol injection.
Re: Staggered H2O/Meth injection
Thanks for that link Wallace, good stuff in there. Lots for me to digest.
And following on what Brent said, is my statement correct? - that alky, in effect, can fool the compressor?, can it extend the range of its map if alky is introduced at about the time it is overspun/pushed too far?
Re: Staggered H2O/Meth injection
So let me ask this, "If The right mix of Meth/H2O is injected pre-compressor and it evaporates completely, thus lowering the pressure, will it cause a low pressure pre comp and a higher pressure post comp and help with spool?" This would only be for a short period, but could help offset the slow down of the turbo when injection first starts.
Re: Staggered H2O/Meth injection
Remember the compressor map is just a guideline and derived in a controlled environment which includes a standard ambient temperature for testing. This is so you can compare apples to apples when selecting a compressor. Lowering the ambient temperature will provide more oxygen for a given PR I still believe you have the same efficiency set by the design of the compressor.
Re: Staggered H2O/Meth injection
I would not overspin a compressor no matter what if you are looking for longevity. Its silly to even think about eroding your compressor wheel if you are overspinning the turbo. You will kill the turbo before it matters. I don't think any amount of injection will give you enough margin to punish your turbocharger physically. Better off selling your turbo and buying one you won't overspin than killing it and having to buy a new one while owning a worthless piece of junk. Overspin failures are nasty.
Re: Staggered H2O/Meth injection
Yes, of course, "overspin" is a poor choice of words. More precisely, when the compressor is operating near the right or upper edges of its map, where it is about to cross over into inefficiency, or . . . . . if it is in its sweet spot but about to be pushed to the less efficient upper right, then, at that moment, the introduction of air at a lower temperature at the inducer, and through the snail, by way of alky, will move the map back toward the lower left - back toward or into the sweet spot, right?
Re: Staggered H2O/Meth injection
Intorducing a higher density media into the compressor doesn't "move" anything on the map. The efficiency is rpm and pressure driven. The higher intake density only changes the numbers on the X-axis.
Just because the compressor map doesn't have information on either side doesn't mean there is "nothing" there. It just means that the manufacturer didn't publish that information. There is actually information to the left of the surge line. That line is arbitrarily "chosen" by an engineer to protect the compressor from being used in the "danger zone". The lack of information off to the right is there because the manufacturer determined that the compressor was not efficient enough to advertise it. It doesn't mean it can't do it.
Now, the turbo overall does have a "redline" for rpm. Within the rpm range that is published on the compressor map the turbo is supposed to be able to operate for the full intended life cycle of the part, and possibly more. Going outside of that range most likely will reduce that life as the number of cycles is multiplied (kinda like dog years as an example) over the same time period of use. The wheels are only capable of withstanding a certain load for a certain amount of time. When running over the "redline" there is possibilities of running into vibrational harmonics, and plain just overloading the wheel. Both can lead to catastrophic failure, which as Brent pointed out, is FUGLY!!
Anyway, point being is that for the most part, don't think about "moving" anything on the compressor map when introducing a different density substance into the compressor. Yes, temperature will affect efficiency, but this is a variable that, unless is super critical and can be controlled, needs to be ignored. If you are needing to know the exact effect on your engine, then you need to monitor your engine under operating conditions. This is an area where theory and math are pretty much a waste.
Re: Staggered H2O/Meth injection
Lower the inlet temperature and for the same PR you've got more oxygen. So without increasing the boost you get more power....right?
Re: Staggered H2O/Meth injection
Yup, but it has nothing to do with compressor efficiency. If you take a temperature reading across the inlet and outlet, as long as the compressor is spinning the same rpm and producing the same PR, the only thing that has changed is density.
Re: Staggered H2O/Meth injection
Please forgive my elementary ignorance of physics - but . . . . . density = mass/volume. And temperature affects volume . . .. and it all goes to how many molecules of oxygen are pumped.
This guy, on you tube is good
Boyle's Law - Pressure & Volume
https://www.youtube.com/watch?v=11BkIYy4rf0
Charles's Law - Volume & Temperature
https://www.youtube.com/watch?v=HgcVglzGl7M
Avogadro's Law- Moles & Volume
https://www.youtube.com/watch?v=Nk8pPH9eh6o
Dalton's Law - Gas Mixtures
https://www.youtube.com/watch?v=tEIpukK8CKM
Gas Density & Molar Mass
https://www.youtube.com/watch?v=wlpvFWxY0x0
Re: Staggered H2O/Meth injection
Quote:
Originally Posted by
johnl
Please forgive my elementary ignorance of physics - but . . . . . density = mass/volume. And temperature affects pressure and volume . . .. and it all goes to how many molecules of oxygen are pumped.
Fixed :thumb:
Ideal gas law: PV=nRT
P= pressure
V= volume
n= molar mass of the substance
R= universal gas constant
T= temperature
You can not change one factor without it directly affecting another. In our case we aren't changing the pressure or the volume. The temperature gets lower, so the only thing that can change in order to keep everything balanced is "n", the molar mass. This makes perfect sense since we are no longer ingesting only air. We have now added another substance to what the compressor is dealing with.
Because of this, you are now dealing with a more dense substance (there is more mass for the same volume) going in and coming out of the compressor. The only thing that changes on the compressor map graph is the numbers on the X-axis because the mass is higher than what is tested, so the mass flow goes up as well. You are not running a different pressure ratio, so the rpm doesn't change.
I suppose you could think about it as shifting the entire map over to the corrected mass flow, but then that makes your graph dynamic simply because you don't inject the methanol all the time.
Re: Staggered H2O/Meth injection
Not all of that density increase is the fluid that's been introduced some portion is more of the denser air that's a result of the temperature drop at the inlet.
Re: Staggered H2O/Meth injection
LOL. Reaper 1, thanks for that correction - it goes precisely to my blind spot.
That admitted, as happens often in the Politics & Religion sub forum, I now seize upon the one part of what you said for vindication -
"I suppose you could think about it as shifting the entire map over to the corrected mass flow, but then that makes your graph dynamic simply because you don't inject the methanol all the time. "
and that is the point of my question - going to how to stage the injection. Staging IS dynamic, it's OK to be dynamic. That is, would you all agree that injection pre-compressor should be secondary, delayed until the compressor is well into the sweet spot of its map, and then, at that moment, give the boost curve a second life by shifting the entire map to the northeast, with a spray of 50/50?
Further, post-IC/pre-TB is where the primary 1st stage spray would begin and at a lower boost level.
In other words, the Hobbes switch for the pre-compressor nozzle would be set to turn on at a higher boost pressure than is the boost point setting of the Hobbes switch that turns on the pre-TB nozzle.
Re: Staggered H2O/Meth injection
If you do set this up I would really like to know if spraying in the inlet has any affect on spoolup. It would require spraying before the spoolup has occurred.
Re: Staggered H2O/Meth injection
Actually, the idea is to spray into the compressor well after spool up, for two reasons, first, as you say, to minimize any loss of inducer speed from the additional mass of the colder air caused by the 50/50, and second, in Reaper1's phrase to "shift the map" of the compressor, at the point where it needs to be shifted, dynamically, again, with the increased mass of the colder air created by the 50/50's evaporation. If you hit the compressor with 50/50 down low, before it is spooled, before it is making any heat, then you aren't optimizing. Hit it later, after its spooled, when heat is a problem. Meanwhile, hit the TB and plenum with 50/50 to lower combustion temps/suppress detonation, and most importantly - allow more timing. As a bonus, you can pull some of that fuel you otherwise are using for combustion coolant.
Re: Staggered H2O/Meth injection
Quote:
Originally Posted by
wallace
Not all of that density increase is the fluid that's been introduced some portion is more of the denser air that's a result of the temperature drop at the inlet.
I'm going to agree with you somewhat. The reason I say "somewhat" is because yes, we are cooling the air down and that will cause the air to condense. However, we are introducing another substance into the volume and that will take up most (I'm going to stay away from the absolute "all") of the displaced volume of the condensed air.
Also remember that the molar mass of the gas is now higher. I'm not a chemist (I hate chemistry, but I understand the basics), but in order to know what that change is you would have to know the molar mass of the injected compound and then use the percentage (I think based on volume?) to calculate the new molar mass. I'm going to take a stab at it and say the difference isn't going to be extreme.
Quote:
Originally Posted by
johnl
LOL. Reaper 1, thanks for that correction - it goes precisely to my blind spot.
That admitted, as happens often in the Politics & Religion sub forum, I now seize upon the one part of what you said for vindication -
:thumb: We are all in this together. I'm just trying to help, that's all. I don't mean to come off as a d*ck or anything. I just want to throw that out there. :thumb: (hooray for intarwebz misunderstandings!!)
Quote:
Originally Posted by
johnl
"I suppose you could think about it as shifting the entire map over to the corrected mass flow, but then that makes your graph dynamic simply because you don't inject the methanol all the time. "
and that is the point of my question - going to how to stage the injection. Staging IS dynamic, it's OK to be dynamic. That is, would you all agree that injection pre-compressor should be secondary, delayed until the compressor is well into the sweet spot of its map, and then, at that moment, give the boost curve a second life by shifting the entire map to the northeast, with a spray of 50/50?
You are correct, there is absolutely nothing wrong with dynamic. It's just harder to picture and to explain.
Re: Staggered H2O/Meth injection
No problems, never were any; you're posts are valuable, instructive.
I read somewhere that the ratio is 3:1; that is, for alky injection, for each three parts of intake air volume reduction from decreased temps due to vaporization of the alky/water, there is one part of offset - of increase in volume - derived from the water/alky's vaporization. To restate it, as the fluid vaporizes, yes, it expands when it is transformed from liquid to gas, BUT the heat it sucks out of that hot compressed air as it vaporizes, reduces the volume of that hot air by an offsetting 3:1 ratio. This fact, after all, is why we are interested in it. I'll try to find the reference to see if I'm re-stating it correctly.
On delaying pre-compressor spray until well into/after spool up, another way of thinking about it is that the ratio of the inertia of the mass of the spray (the weight of the gas/fog/mist) to the inertia of the spinning inducer is more favorable. That is, at or near full inducer speed, the inertia of the spray is totally overpowered by the inertia of the inducer where at low boost/beginning of spool, the spray, reportedly, does slow spool.
Re: Staggered H2O/Meth injection
Isnt the whole idea of injecting pre compressor to actually get more air in? You can inject after and lower the charge temp....but you're not packing more air molecules in just lowering the temp of what's been compressed.....just like an intercooler. I agree the air mass would increase with the fluid introduced. Think about the difference in power in summer vs winter...way more power since the air is denser and drier. I would think the pre compressor injection should fall somewhere in between...the fluid if completely vaporized would be similar to the humidity in the air. Some % of the power increase in winter would be due to lower humidity and some because the air is denser? Great discussion btw.
Re: Staggered H2O/Meth injection
Thanks Wallace, your participation is appreciated. This subforum should be more active, the possibilities for our cars, especially T1 cars, are too cheap/simple and too great to be neglected. And, with an intercooler and pre turbo and post IC injection, I wonder "how low can we go?"
Re 3:1 expansion ratio, look at the last post here -
http://www.eng-tips.com/viewthread.cfm?qid=283133
And this is a really good discussion too -
http://www.eng-tips.com/viewthread.cfm?qid=314358
Injection after the turbo/after the IC/before theTB does more than just lower IAT, the water when it is in the combustion chamber absorbs heat and in doing so delays the pressure spike that results in detonation. It can do a better job of that than a too rich mixture of gasoline. It also enables more ignition advance. Meanwhile, the pre-turbo injection mimics a bigger turbo and allows more total air/oxygen.
2 Attachment(s)
Re: Staggered H2O/Meth injection
Ordered one of these with a jet - goes in front of the turbo compressor inlet.