Alky & Air - mass flow velocity & energy calculation . . . . .
- Thread starter Jerryl
- Start date
This thread makes me feel like a complete retard!!
Keep reading. There's great info here and maybe you can keep from blowing your car up. This board is priceless to my relatively minor successes with these cars.
This brings up some great questions to ask. The primary means that the air is cooled is through evaporation of the atomized droplets of alky. Not all of the air is vaporized. Some of it makes its way into the chambers and is vaporized there. The big question is what happens if none of the alky is vaporized and instead it remains atomized in the air. Will it still be equally distributed to the cylinders? You are saying that it doesn't and more will make it way to the rear cylinders, richening them compared to the front cylinders.
Naturally, more of the alky will vaporize at higher inlets temperatures of the compressed air. But apparently there could be a certain temperature where if enough alky doesn't vaporize it will richen up the rear cylinders more than the front cylinders? We don't even know what percentage of alky is vaporized to begin with and if it even affects anything. I figure if this was indeed happening then the rear cylinders would always be slightly rich since 100% of the alky doesn't vaporize anyway. This should show even failure rates between the #1 and #2 cylinders. However, #1 is the usual culprit which leads me to believe it is more a fueling issue with #1 the weakest link.
And if there is a certain temperature where this effect comes into play, that means that it should be directly related to the temperature of the compressed air after the intercooler. So for example, my buddy has a crappy intercooler and is running his turbo on the edge of his efficiency range. That means his air temp will be very high even in very cold weather so he won't have to worry about his alky system. Lets say my car has a very efficient intercooler and I'm running a bigger turbo in a very efficient area on the map. My compressed air temps will be much cooler than my buddy's so I should encounter alky problems at much higher ambient temps than my buddy would. So this means my buddy could have no issues in 0 degree weather while I may have to be careful in 60 degree weather because we will both be running the same compressed air temps after our intercoolers. This seems ridiculous and there are so many variables in this situation how can we compare one car to another?
There is no way one can say that cold temperatures are affecting the alky distribution without some data or at least some real scientific numbers to back it up. Its a crapshoot at best. To even begin to think that this could be happening you first have to verify the A/F and the alky system intergrity/pressure to rule them out, which means logs. And you should see equal failures between #1 and #2 which hasn't been the case. At a minimum, one can calculate the amount of alky being injected, the temp the air is cooled by the alky, and from that get a rough estimate of the % of alky being evaporated for different conditions. And you still have to prove that the atomized (non evaporated) alky doesn't get distributed evenly. There isn't a bit of evidence yet to support it, just some guestimation.
Is it possible? Sure. But I think its a bit premature to be stating it as fact when there are so many unknowns. I have been thinking of getting a multiple EGT setup that would shed some light on this. Alternatively, I could get a second channel and EGT and put one on #1 and a second on #5 and see if the ratio changes in cold weather. Since I am dual feeding the fuel rails and logging alky pressure I will be able rule out #1 fuel delivery issues and alky pressure issues. This is the only way to know.
Stupid question of this thread...
If you are one of those people who makes big power and injects a lot of alky, what would happen if you injected some or all of the alky upstream of the intercooler on cold days? The hot, high pressure air at that location would ensure that the alky would evaporate. By doing this correctly, you could ensure that the air coming out of the intercooler was the same as ambient, or even lower than ambient, depending how much alky was injected upstream. On a cold day, this would be a pretty low temperature. Then, a small amount of alky injected after the intercooler could bring it down below ambient with lower risk of puddling.
A simple valve and two lines/nozzles could be used to chose whether to inject upstream or downstream of the IC.
I'm sure somebody will tell me why this won't work...
Mike
Sent from my HTC Droid Incredible using Turbo Buick
If you are one of those people who makes big power and injects a lot of alky, what would happen if you injected some or all of the alky upstream of the intercooler on cold days? The hot, high pressure air at that location would ensure that the alky would evaporate. By doing this correctly, you could ensure that the air coming out of the intercooler was the same as ambient, or even lower than ambient, depending how much alky was injected upstream. On a cold day, this would be a pretty low temperature. Then, a small amount of alky injected after the intercooler could bring it down below ambient with lower risk of puddling.
A simple valve and two lines/nozzles could be used to chose whether to inject upstream or downstream of the IC.
I'm sure somebody will tell me why this won't work...
Mike
Sent from my HTC Droid Incredible using Turbo Buick
i have pulled the plugs on various tunes and even on a tune with 50 base psi on the rail with twin pumps,max wot on the tt chip60lb injectors,29psi of boost,duel m10's,afr 10.5,0.0 knock.the plugs looked good and didnt show huge differences.i havent pushed the car like that in a while or for a long time,it was a beat down tune.i run alot richer afr (9.8 to 10.2)now with lower boost,rail pressure and lower wot,but now on an m10 m15.i havent had a problem with the richer afr's.the only problems i have seen is when the afr goes lean and the stronger cars dont allow you to make mistakes like that.i have noticed in the hotter air my car seems to want a little more alky,in the colder temps more fuel.
- Joined
- May 28, 2001
How about using a dual nozzle set up to do exactly that? One nozzle lined up with the inlet of the intercooler and leave the other one in the up pipe where it normally sits?
Jerryl
Tall Unvaccinated Chinese Guy
- Joined
- Dec 14, 2004
Well, I got some help on the review of this. . . . . . Changed the temp . . . . .
Lets say . . . . 120F air charge, Mass flow 60lb/min or 600 hp est., 25 PSI
Air at 120F and 25 psig = 0.185 lb/ft3, so 60 lb/min of that is 60/0.185 = 324 acfm (about 830 afcm at the compressor inlet)
So in a 2.25” opening that would be 195.8 ft/s, or 133.5 mph.
Lets say . . . . 120F air charge, Mass flow 60lb/min or 600 hp est., 25 PSI
Air at 120F and 25 psig = 0.185 lb/ft3, so 60 lb/min of that is 60/0.185 = 324 acfm (about 830 afcm at the compressor inlet)
So in a 2.25” opening that would be 195.8 ft/s, or 133.5 mph.
- Joined
- Feb 18, 2006
Great thread!
So many different ways we could go about fixing this issue. We tend to make things more complicated than they need to be. Based on Don's set up I have some ideas for direct port injection. That is the 100% rock solid way to ensure equal distribution.
RL
So many different ways we could go about fixing this issue. We tend to make things more complicated than they need to be. Based on Don's set up I have some ideas for direct port injection. That is the 100% rock solid way to ensure equal distribution.
RL
Well . . . more calcs.
A typical Air/Air IC is about 60-70% efficient.
I am going to use 75% because of all the $$$$ spend on the IC’s.
Boost pressures raise charge temp at 11F / 1 lb boost.
Lets look at the temps before / after IC at typical boost pressures with alky (23 PSI)
If we study this model you will see that we made some assumptions.
The assumption is that the IC efficiency is constant with temp changes, and results in linear temp changes.
So, we also see that at 10F ambient, the charge temp out of the IC is still around 70F.
This the temp that the meth is initially exposed to . . . . and this happens at some volume of air that will put most vacuum cleaners to shame. (LOL!)
The temp after the methanol will drop significantly if the charge temp is high.
My real life data collection shows about 40-45% temp reduction on a non-IC’d set-up.
The better the IC, the less the delta temp.
Ambient - 50
Boost -23
IC Efficiency -75%
Charge temp Before IC -303
Charge temp after IC - 112
Ambient - 40
Boost -23
IC Efficiency -75%
Charge temp Before IC -293
Charge temp after IC - 102
Ambient -30
Boost -23
IC Efficiency -75%
Charge temp Before IC -283
Charge temp after IC - 92
Ambient - 10
Boost -23
IC Efficiency -75%
Charge temp Before IC -263
Charge temp after IC - 72
I'm no physics expert so..... Based on the above info suppose I provided the following info:
Ambient - 80
Boost - 20
IC efficiency - ??
Charge temp before IC - ??
Charge temp after IC - 99
What assumptions can you draw from this limited info??
Jerryl
Tall Unvaccinated Chinese Guy
- Joined
- Dec 14, 2004
Well, great question Dave!
First off, I am no physics expert. Heck I don’t even know enough to be dangerous. LOL
The credit for 99% of these calculations go back to the previous work completed by John Estill.
That is NOT to say that he accepts any CREDIT FOR MY ERRORS!
Anyway . . . .
There are assumptions and calculations that have to be made in any hypothesis.
Assumptions made is a turbo efficiency of 74%, which combined with ambient temp and inlet restriction assumptions gives calculated charge temps at XX boost out of the compressor.
Another assumption is IC efficiency of 75% as stated. With this number, we can calculate the temp reduction of the IC at boost.
If you assume 600 HP or around 60lb/min, you can calculate the air flow required (acfm) to make that amount of HP.
If you know air flow AND the TB size, you can calcite the speed through the TB.
Once you know the speed, you can get an appreciation of what is going on.
With all these assumptions, I can make a BIG A$$ of myself, but we have to start thinking in terms of “micro cause and effect event”. . . . . .
The whole idea is to build a hypothesis and get an appreciation of the air velocity through the TB and the associated forces.
Probably too many assumptions..... Let's say about 375 hp, that's what my track speeds and car weight dictate. TE44 turbo.... IC tubing is all the same size as the stock 86 up pipe. IC is a CAS V2..... Throttle body is a 62mm.... Any of that help?
TurboDave said:
You need the engine speed and displacement (so you can calculate the cfm) and the size of throttle body in cross sectional open area. The turbo or lack of one doesn't matter and either does the power. You could have vacuum there or 100psi. Cfm is cfm. You can have 100psi and. Zero cfm.
Jerryl
Tall Unvaccinated Chinese Guy
- Joined
- Dec 14, 2004
Correct!
If we know the mass flow rate (lbs/min) and the temp, we can calculate the density of the air and get to the volume (CFM).
I define "mass flow rate" as not static but actual flow of a certain mass of air at actual of std temp, over a given time period.
In this case we determined that we are using 60lb/min at 120F, so we know what the actual air volume in a given period would be. (830 acfm)
Here is an interesting link to which I know nothing about
to mass flow rate.http://exploration.grc.nasa.gov/education/rocket/mflchk.html
Good eye, Dave. Efficiency is basically out/in, so there is no way the IC can stay at the same efficiency. If your delta T changes that is going to effect your efficiency.
Good thread. I've mentioned before how I've had to lower my alky in colder temps because of the same reasons, but most looked at me like I was retarded.
Jerryl
Tall Unvaccinated Chinese Guy
- Joined
- Dec 14, 2004
Dave,
340gr/sec = 340 X 60 sec/min x 0.00220 lb/gr = 45 lb/min
So if you are calculating 375 WHP based on MPH, your drivetrain loss is 17%, and that is very realistic.
Correct! The delta T will vary based on many variables, but no one can measure all the variables, unless it is under very controlled conditions (Like in a lab) with some $$$$$$$$$$$erious equipment.
And even than, we would have a very hard time drawing any valuable conclusions to the affect of EACH of the variables such as; Humidity, wind speed, baro, attack angle, surface cleanliness, actual intake air temp based on speed, inlet restriction based on RPM, turbine speed/efficiency . . . . . . you get the picture. So we have to make assumptions just like we all do every day. Here is an assumption; Adding a bigger turbo will make the car faster. True?- No. False? -No.
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