Alky percentage to fuel ratio and tuning for it, numbers not matching

tonka

Member
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.

View attachment 163088

I'd definitely agree that most if not all vaporization takes place in the cylinders. If you look at the specs for methanol, it takes a lot of energy to change it from a liquid state to a vapor state. Which gives that great cooling effect we need. It takes time for that energy to be absorbed by the methanol for it to change states though. There's where the droplet size probably makes the difference in the percentage vaporized during the short time it remains in the cylinder.
 

norbs

Classic fast, XFI, SPortsman & MS3 programming
OK all these calculations are great, and if your tuning the same AF as you would for gas, you will hurt the motor , the whole idea of this topic is calculate the af we need based on the % of mixture of alky in the fuel. So how can we come up with the right proven formula?
 

murphster

Well-Known Member
Ok, time to start over and try some new numbers. Doing some reading on the methanol cars it looks like for boosted applications on big power they recommend close to 4.5 a/f ratio for max power and 4.0 a/f ratio to be safe. I read that methanol makes the best power 30% richer than stoich while gas makes best power 20% richer than stoich. So that means we need to richen it up as we add more meth. If we convert these numbers to lambda for methanol and weight the lambda's for gas and meth by the % fuel of each maybe that would give us an a/f goal by %meth.

At the real nozzle pressures of >150 psi on a dual nozzle setup we are flowing a lot of meth. Around 40% meth seems reasonable for someone running in the mid to low 10s getting full pressure on the nozzles at WOT.

For the low meth a/f ratios I had to find a new lambda table for meth:
lambda methanol.jpg

So I will assume the following numbers for the calcs:

gas:
power a/f=12.0, lambda=0.82
safe a/f=11.5, lambda=0.78

meth:
power a/f=4.5, lambda=0.70
safe a/f=4.0, lambda=0.63

calc for 40% meth:
power (0.6 x .82)+(0.4 x.70) = .77 lambda = 11.4 gas a/f
safe (0.6 x .78)+(0.4 x.63) = .72 lambda = 10.6 gas a/f

The 10.6 a/f number seems reasonable. A quick guess on the numbers for a single nozzle gives me 11.0-11.2 gas a/f.
 

SloGN

I'm a ASSHOLE.....
This thread is very interesting. But I thought the wideband is measureing the amount of oxygen left in the exhaust charge after combustion? If thats the case how would the different types of fuels change that. I understand some fuels are oxygenated. I also understand that different fuels have a much different energy storage with in them. So with that you would need more or less of that fuel to make the same power/heat. But how does that effect the o2 reading.
 

tonka

Member
Ok, time to start over and try some new numbers. Doing some reading on the methanol cars it looks like for boosted applications on big power they recommend close to 4.5 a/f ratio for max power and 4.0 a/f ratio to be safe. I read that methanol makes the best power 30% richer than stoich while gas makes best power 20% richer than stoich. So that means we need to richen it up as we add more meth. If we convert these numbers to lambda for methanol and weight the lambda's for gas and meth by the % fuel of each maybe that would give us an a/f goal by %meth.

At the real nozzle pressures of >150 psi on a dual nozzle setup we are flowing a lot of meth. Around 40% meth seems reasonable for someone running in the mid to low 10s getting full pressure on the nozzles at WOT.

For the low meth a/f ratios I had to find a new lambda table for meth:
View attachment 163188
So I will assume the following numbers for the calcs:

gas:
power a/f=12.0, lambda=0.82
safe a/f=11.5, lambda=0.78

meth:
power a/f=4.5, lambda=0.70
safe a/f=4.0, lambda=0.63

calc for 40% meth:
power (0.6 x .82)+(0.4 x.70) = .77 lambda = 11.4 gas a/f
safe (0.6 x .78)+(0.4 x.63) = .72 lambda = 10.6 gas a/f

The 10.6 a/f number seems reasonable. A quick guess on the numbers for a single nozzle gives me 11.0-11.2 gas a/f.

These numbers fit pretty well with what I've been seeing at the track so far this year. I know at a 125-127mph power level a 10.3 a/f causes me to lose 5-6 mph. Anywhere from a 10.8 to 11.3 a/f I don't see much variance in mph, so I just keep it in the upper 10s. Of course, install location and brand of wideband seem to effect readings for everyone differently. As I turn it up this year we'll see how those targets change.
 

bison

Moderator
Staff member
tonka said:
These numbers fit pretty well with what I've been seeing at the track so far this year. I know at a 125-127mph power level a 10.3 a/f causes me to lose 5-6 mph. Anywhere from a 10.8 to 11.3 a/f I don't see much variance in mph, so I just keep it in the upper 10s. Of course, install location and brand of wideband seem to effect readings for everyone differently. As I turn it up this year we'll see how those targets change.

Ive never lost 5-6mph on any pass even dropping the targets into the 9's. 20-30whp loss on a dyno was typical on a 600+whp combo dropping a/f from 11.3 to 10.2 or so. Nothing that would cause a loss of 5 mph though. Mass efficiency of the engine plays a large role in what target would be considered safe. If you're over 70 lbs/min and you are dual nozzle and 11:1 or leaner you're asking for trouble.
 

murphster

Well-Known Member
Ive never lost 5-6mph on any pass even dropping the targets into the 9's. 20-30whp loss on a dyno was typical on a 600+whp combo dropping a/f from 11.3 to 10.2 or so. Nothing that would cause a loss of 5 mph though. Mass efficiency of the engine plays a large role in what target would be considered safe. If you're over 70 lbs/min and you are dual nozzle and 11:1 or leaner you're asking for trouble.

It definitely seems like being on the rich side doesn't hurt performance too much with methanol. Since its oxygenated it can be run at very rich levels. I'm surprised you only saw a 20-30 whp loss though. Would have thought it would be more. Even if the numbers I ran are somewhat accurate, if lowering the a/f ratio a couple more points doesn't hurt performance then that seems the way to go.
 

Razor

Forum tech Advisor
Staff member
Gone for week.. great thoughts.
FWIW my fastest pump gas customer runs 9.6:1 AFR, 3400 lb car, 24 psi, 160 mph trap.

I run mine on a 10.5:1 AFR target and no hiccups at that AFR. Last full pass was 155 mph
 

Mr.Spool

Well-Known Member
ive run mine down to 9.3 no problems.saw no difference in mph from 9.9 to 9.6 afr.i can say 11.0 took the top of a plug off.
 

tonka

Member
Ive never lost 5-6mph on any pass even dropping the targets into the 9's. 20-30whp loss on a dyno was typical on a 600+whp combo dropping a/f from 11.3 to 10.2 or so. Nothing that would cause a loss of 5 mph though. Mass efficiency of the engine plays a large role in what target would be considered safe. If you're over 70 lbs/min and you are dual nozzle and 11:1 or leaner you're asking for trouble.

Woops, didn't look close enough at my slips. My power loss was from the DA and humidity that day, and not adjusting for it. Sorry for the misinfo guys.
 

imjoesnuffy

I just break stuff!
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.

Brian,

Can you elaborate on this? In my limited experience tuning with meth injection, this is what I have seen. M10 and M15 nozzles: Normally I target 10.8 in 1/2 gear and 10.5 in 3rd. As the air temps and DA drops I try to richen it up by targeting 10.0 in 3rd. So far it has worked well for me(no HG replacement in 2 years), but I have never made any changes to the timing. 25 in 1/2 gear and 22 in 3rd. Shifting around 6000 rpm, am I leaving anything on the table by not lowering the timing?
 

tonka

Member
Modifying what Murphster had posted, with slightly richer a/f numbers:
gas:
power a/f=11.5, lambda=0.78
safe a/f=11.0, lambda=0.75

meth:
power a/f=4.0, lambda=0.63
safe a/f=3.7, lambda=0.58

calc for 20% meth:
power (0.8 x .78)+(0.2 x.63) = .75 lambda = 11.0 gas a/f
safe (0.8 x .75)+(0.2 x.58) = .716 lambda = 10.6 gas a/f

calc for 30% meth:
power (0.67 x .78)+(0.33 x.63) = .73 lambda = 10.75 gas a/f
safe (0.67 x .75)+(0.33 x.58) = .69 lambda = 10.2 gas a/f

calc for 40% meth:
power (0.6 x .78)+(0.4 x.63) = .72 lambda = 10.6 gas a/f
safe (0.6 x .75)+(0.4 x.58) = .68 lambda = 10.0 gas a/f

I haven't run straight race gas in a long time, so maybe 11.0/11.5 is too rich for gas alone, just what I recall from the past from others.
 

murphster

Well-Known Member
Ok, time to start over and try some new numbers. Doing some reading on the methanol cars it looks like for boosted applications on big power they recommend close to 4.5 a/f ratio for max power and 4.0 a/f ratio to be safe. I read that methanol makes the best power 30% richer than stoich while gas makes best power 20% richer than stoich. So that means we need to richen it up as we add more meth. If we convert these numbers to lambda for methanol and weight the lambda's for gas and meth by the % fuel of each maybe that would give us an a/f goal by %meth.

At the real nozzle pressures of >150 psi on a dual nozzle setup we are flowing a lot of meth. Around 40% meth seems reasonable for someone running in the mid to low 10s getting full pressure on the nozzles at WOT.

For the low meth a/f ratios I had to find a new lambda table for meth:
View attachment 163188
So I will assume the following numbers for the calcs:

gas:
power a/f=12.0, lambda=0.82
safe a/f=11.5, lambda=0.78

meth:
power a/f=4.5, lambda=0.70
safe a/f=4.0, lambda=0.63

calc for 40% meth:
power (0.6 x .82)+(0.4 x.70) = .77 lambda = 11.4 gas a/f
safe (0.6 x .78)+(0.4 x.63) = .72 lambda = 10.6 gas a/f


Just wanted to update this......

On the first post we can calculate how much fuel and methanol is injected to get the % of methanol. At 140psi alky this gives 117.4 lbs/hr for an M15 nozzle and 78.2 lbs/hr for an M10 nozzle for a total of 196lbs/hr for the typical dual nozzle setup from Razor.

But using this to calculate total HP didn't make sense. Thats because like E85 we need to burn a lot more alky compared to gas to get the same power. Using the ratio of stoich A/F ratios of 6.4 for meth and 14.7 for gas we get a ratio of .435. So if we inject 196lbs/hr of meth we should only use .435 x 196 = 85.3lbs/hr for HP calculations. Using a BSFC of .5 gives me the best results resulting in a simple formula of total fuel (lbs/hr) x 2 = HP.

Using this with my car..... I was at 63% duty cycle last time out on an M15 and M10 nozzle.

83 lbs/hr x .63 x 6inj = 313.7 lbs/hr
196 lbs/hr meth x .435 = 85.3 lbs/hr gas equiv

Total = 399 lbs/hr. Est HP = 399 x 2 = 798HP. Almost right on with my timeslips.

For my truck, I'm using a single M15 nozzle and running 50lb injectors at 50%.

50 lbs/hr x .50 x 6inj = 150 lbs/hr
117.4 lbs/hr meth x .435 = 51 lbs/hr gas equiv

Total = 201 lbs/hr. Est HP = 201 x 2 = 402HP. This needs to be verified but at least gives me a way to estimate how much HP I am making.

I would still use the raw total lbs/hr of meth injected for what A/F you should run For my truck on the single nozzle I am at 51/201 = 25% meth.

Using the formula and table in my quoted post.....
A safe A/F est: (0.75 x .78)+(0.25 x.63) = .74 lambda = 10.9 gas a/f

So even though its a single nozzle not making near as much power, since the injectors are small and the M15 still puts out a lot of alky I have 25% meth as my total fuel and if the formula is right I should stay at 10.9 A/F to be safe.
 
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