Alky percentage to fuel ratio and tuning for it, numbers not matching
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what is a inmo gas?
If i do the calc for 11.5 AF using pump gas with no ethanol fuel ,it is as follows:
EQ AF=[(add%*add_stoich)+((1-add%)*14.7))/14.7] x Desired gas AF
EQ AF=[(.9)+(13.23)/14.7] x11.5=11.05AF
jpwalt1987
Well-Known Member
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norbs said:
In my Opinion.
Is all the 93 blended with 10% ethanol up north ?? We have straight gas on the gulf coast.
Im gonna take a stab at this, let me know what you think. From what we're seeing/hearing, a twin nozzle system with an M10 & M15 runs approx. 140psi, give or take. In Bison's example, he is running two M10 nozzles, which is netting him approx 180 psi either by itself or through additional means. Now from reading this http://www.fluidproducts.com/engineer.htm , he has the advantage of lower flow nozzles (in effect) which leads to a smaller droplet size. He also has the advantage of higher pressure, which also leads to smaller droplet size. The smaller methanol droplets will be easier to vaporize. I have a feeling the rest of the answer lies here http://racecarbook.com/bobsblog/methanol-fuel-temperature/ . He mentions that only the vaporized methanol will burn, and apparently the larger methanol droplets do not spend enough time in the cylinder to achieve full vaporization. My guess is your calculations of meth injected versus burned may actually make sense--the rest may very well be going out the tailpipe. Bison may be getting away with less methanol injected due to better vaporization. That 5000 Horsepower on Methanol book looks like it could be a good read.....
Thats asking a lot
NEW AF=[(Meth% x 6.40)+(Ethanol% x 9)+([1-(Meth%+Ethanol%)] x 14.7)] / 14.7 x Gas a/f
Example for 25% meth and 10% ethanol seeking the new a/f ratio equivalent to 11.5 on gas:
= [(0.25 x 6.4)+(0.10 x 9)+([1-(0.25+0.10)] x 14.7)] / 14.7 x 11.5
= [(1.6)+(0.9)+(9.555)] / 14.7 x 11.5
= 12.055 /14.7 x 11.5
= 9.43
So for 10% ethanol mixed in with gas multiply the following ratios times the Gas a/f:
15% meth: 0.88
20% meth: 0.85
25% meth: 0.82
I knew the numbers weren't going to be pretty once you added in the ethanol. This says that to get an equivalent of just 11.8 gas a/f on only 15% meth you should be shooting for 11.8 x 0.88 = 10.38. Running low 10s or faster you're probably higher than 15% meth and probably want to shoot closer to 11.5 so it seems like we could be on the lean side.
Another issue is that its hard to tune for these kind of a/f ratios on a stock ECU setup without being very rich on street driving. I've been fine on the stock ECU but its starting to show its limitations as I lower the a/f ratios at WOT for the higher HP levels with meth injection. On a TT 6.1 chip I'd have to keep my base fuel real low and depend on the correction to add fuel up top. A TT SD chip has more options but you'd still run into the same problems. Seems like FAST or similar would be the way to dial it in across the whole rpm/boost range to keep correction to a minimum (keep in leaner for highway and lower boost and have a nice transition to the rich a/f ratios for high boost).
Another issue is that its hard to tune for these kind of a/f ratios on a stock ECU setup without being very rich on street driving. I've been fine on the stock ECU but its starting to show its limitations as I lower the a/f ratios at WOT for the higher HP levels with meth injection. On a TT 6.1 chip I'd have to keep my base fuel real low and depend on the correction to add fuel up top. A TT SD chip has more options but you'd still run into the same problems. Seems like FAST or similar would be the way to dial it in across the whole rpm/boost range to keep correction to a minimum (keep in leaner for highway and lower boost and have a nice transition to the rich a/f ratios for high boost).
Am I missing something here? The a/f ratio showing on the wideband in the gas scale will always have stoich at 14.7 regardless of fuel.
For an example....e85. If you still use a gas scale....which I do...you still consider 14.7 stoich and tune for your normal 11.0 or whatever your target af is. Why would a gas/meth mixture be any different? I'm lost here.
I've seen data logs and a tune from a well known tuner and he used the gas scale normally when spraying a good deal of meth in a 9 sec car. Also helped tune a few cars myself on meth (these were only low 11 sec cars though) and I used my normal 11.2 or or so af for that power level and had good success.
Are you all saying that the WB should be reading low 10's and stoich should be considered in the 12's or so? I have to disagree if so. I don't see it any different then tuning with e85.
For an example....e85. If you still use a gas scale....which I do...you still consider 14.7 stoich and tune for your normal 11.0 or whatever your target af is. Why would a gas/meth mixture be any different? I'm lost here.
I've seen data logs and a tune from a well known tuner and he used the gas scale normally when spraying a good deal of meth in a 9 sec car. Also helped tune a few cars myself on meth (these were only low 11 sec cars though) and I used my normal 11.2 or or so af for that power level and had good success.
Are you all saying that the WB should be reading low 10's and stoich should be considered in the 12's or so? I have to disagree if so. I don't see it any different then tuning with e85.
You make a great point. These #'s are the actual a/f numbers for these mixtures, no doubt. But if the O2 sensor doesn't read the actual a/f ratio then it doesn't matter since you're tuning to lambda anyway. All in all this is just an exercise to try and get a handle on what a/f ratios to shoot for based on how much meth we are injecting and what power levels we are making.
Based on meth injection calculations we are injecting a large amount of meth. If you know your alky pump pressures and fuel injector duty cycle you can at least get an idea what the meth % of the fuel is.
So we run these richer a/f ratios to make up for the limitations of the methanol since it does raise the effective octane some but its not like race gas. But if you are injecting a lot more methanol at the same power level maybe you can run a leaner a/f ratio because you raised your effective octane due to the increased cooling? However, at low power levels it seems like after injecting a certain amount of methanol it sort of saturates so that it doesn't raise the effective octane and there is no benefit. But at higher power/air flow levels the extra methanol is still effective in raising the effective octane allowing us to make more power.
Based on my current injector #s and calculating the injected meth% I may be as high as 44% meth. People running a dual nozzle setup but not as much injector will have a higher meth% (which is probably most people on a dual nozzle).
The problem I've found has just about all to do with vaporization. The more meth injected and the lower the charge air temp and the higher the engine speed the closer you are to disaster. When the inlet temp is too cool injecting more meth leans out the front of the engine.
I am still not convinced that it has to do with vaporization. I attached a chart showing the saturated vapor pressure of methanol vs different temperatures (http://www.ddbst.com/en/online/Online_Calc_vap_Form.php) . Anything left of the curve is liquid and to the right is vapor. You can see that a 14.7psi (atmospheric pressure) the temp is 149 F, the boiling point of methanol. At 20psi of boost the total pressure is almost 35psi and the boiling point is almost 190F. But with a decent intercooler we are running less than 100F air temp before the meth is injected. We are way above the saturation point on the curve, not even close. This tells me most of the methanol stays is liquid form, i.e. atomized. Not vapor. Sure, some of it is vaporized cooling down the air but we are injecting a ton of methanol on dual nozzle setups. I think most of the methanol remains atomized, not vaporized, and the the biggest effect of methanol injection is cooling down the cylinders, not the air. Since we now know how much methanol we are injecting and what the typical temperatures are after an intercooler and after injection it shouldn't be too hard to calculate what percentage of the methanol is actually vaporized cooling down the air before it gets into the cylinders at different air temps. And this goes back into another point I made in a previous post...... If there is a distribution effect of enriching the rear cylinders it would happen across the temp range because most of the meth remains atomized (not vaporized) throughout these temperature ranges.
Were not looking for 100% vaporization which would happen when it boils. Thats impossible under the condituons. But we are looking for as much vaporization as possible. Its easy to see what happens when you don't have vaporized methanol in a dry flow intake and you are over injecting. It isn't pretty. Most isn't vaporized that is very true. That which isn't is going to favor the rear cylinders. It's easy to see why a port injected setup will trump any pre plenum setup which uses a dry flow engineered intake. If I recall the TAI rules require pre throttlebody injection. I can only roll my eyes at that.
I'm saying the opposite. That we have very little vaporization.
That is, very little vaporization compared to the total amount of meth being injected and the air temp has a minimal effect on this. And as long as the airflow is equally distributed the atomized meth will be equally distributed also.
Another thing I have seen as I read up on this is the difference between water and methanol injection. Water cools the air a lot better than methanol, but it only takes a small amount to do this. The bigger benefits come from the cylinder cooling that methanol provides. That happens because most of the injected methanol remains atomized in liquid droplets and doesn't vaporize until it gets into the cylinders. So again, the question remains is does the atomized methanol get distributed evenly? If it didn't, I think we would see leaning out of the front cylinders evenly distributed across the #1 and #2 and across all temperature ranges as the amount of methanol injected goes up.
Jerryl
Tall Unvaccinated Chinese Guy
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Just saw this thread and signing up to learn some more.
Murphster, those charts are money!
Murphster, those charts are money!
