leaded/oxygenated racing fuel vs. methonal

[StevenStarke]

I currently have a project I am part of we are contemplating on the switch to vp's m5 methonal. We originally were looking into ethonal/e98 but we have yet to see substantial gains over vp's q16.

The project is a 2.3ltr engine making 60lbs of boost, on the fuel we currently run we are making roughly 1250hp. Has anyone made a switch over to methonal and have any data on actual gains?

We are fully aware of the fuel system requirements to make the change over and are willing to do so if need be.

 

[patprimmer]

There are energy gains in the order of 10% by going from typical pump or even the old leaded 115/145 (from memory) av gas.

A second advantage of methanol is the clean burning and the lack of plug fouling even when very rich. This allows extra fuel to suppress detonation which in turn allows more spark advance or more boost, so you only find that if you optimise correctly.

The extra fuel required for a stoichiometric mixture then further enhanced by the ability to run even richer gives a significant reduction in charge temperature all the way to ignition point.

I have seen power losses with methanol if the ignition system is not up to lighting the charge. This is a very common problem with people who claim methanol will not give a power boost. A really good magneto with really tight plug gaps still works best in my experience. Second best is an electronic system with coil on plug but I have yet to see one match a good maggy under really high loads.

The only practical (well kinda), available (well kinda), legal (well kinda) fuel I have seen out power methanol on a properly optimised engine is nitro methane.

I have never been able to reconcile VPs claims and premium prices over 99.9% pure industrial grade methanol.

They sell some extra powerful methanol, but that is actually a nitro blend. If you can legally run that, you can legally run your own blend with the same level of nitro.

If you want a less abrasive fuel than 99.9% methanol, you can add castor oil or some other proprietary methanol compatible lubricant.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[black2003cobra]

The fuel properties table in back of Heywood give the lower-heating values of a stoichiometric mix, for gasoline and methanol to be 2.83 and 2.68 MJ/kg, respectively. Per kg of fuel, the lower-heating values are 44 and 20 MJ/kg, respectively.

 

[patprimmer]

Well if that is the case, Heywood disagrees with every other publication I ever read on the topic. A typo maybe? A difference in handling latent heat of evaporation maybe.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[black2003cobra]

By calculating the heating values and stoichiometric ratios from the fuel compositions and the elemental heating values, I get different results myself, Pat. Nonetheless, those are indeed the values he has listed. Personally, I would tend to doubt they are typos. He does list sources, but I have not researched them.

 

[WolfHR]

Risking to shoot myself in the foot- I seem to recall those numbers should be about right... The (main) power difference should come from different stochiometric ratios- the same charge of air would need more methanol than gasoline (amongst other things because there is some oxygen already in the fuel), hence more energy released.

 

[black2003cobra]

The lower, first set of numbers are for a stoichiometric mix, so the difference in air-to-fuel ratio is already taken into account.

Although alcohol contains oxygen, it is not really the way we want it. In general, the higher the oxygen content, the lower the energy content.

 

[WolfHR]

Yes it is taken into account, but you will not get the same amount/weight of mixture into the cylinder in those two cases. Hopefuly I am not oversimplifying- but one could ignore the volume of the fuel and say that the same volume of the air is used in both cases and the weight of the fuel is the dominant factor for energy content of the mixture. Since both fuels have equalish density one should look into stechiometric ratio to conclude which way the scale tips...

Let me check the numbers (I may have a MathCad file lying around somewhere which I made for similar purpose) and get back on this (with admission of guilt or otherwise).

 

[black2003cobra]

Perhaps just some confusion. Yes, you are correct that there will be a larger mass of fuel in the case of alcohol due to its higher stoichiometric fuel-to-air mass ratio. But again, that effect is already taken into account in the first set of numbers. The first set is basically MJ per kg of air. The second set is MJ per kg of fuel.

 

[WolfHR]

Black2003Cobra, no I think what you've written in that post is correct- first numbers are low heating value per kg of the mix, and as I've suspected values per kg of air are in favour of methanol.

I'm enclosing the comparison of heating values (assuming his numbers for the fuel low heating values) as picture, and will try to see how numbers differ when viewed more 'realisticaly'. But I suspect they will be similar to those per kg of air.

 

[WolfHR]

Pardon me for being a fool and forgetting the attachment.

 

[black2003cobra]

Ah, I see what you were getting at. My apologies. I was the one confused!

Heywood lists sAFR = 14.6 and 6.47 for gasoline and methanol, respectively. So using those along with his values of lower-heating values per kg of fuel, (for consistency), one gets 2.821 and 2.677 MJ per kg of mix, (which seem to agree w/ the values in his table), and 3.014 and 3.091 MJ per kg of air, respectively.

Eric

 

[WolfHR]

I also computed low heating values per cubic meter of mixture (that should be most relevant): and as I presumed when I said I hoped I didn't oversimplify- the difference to those per kg of air are almost negligeable.

In case of low heating value per kg of mixture I got 105,27% higher for methanol, and in case per cubic meter of mixture I've calculated 105,27%... HTH

 

[black2003cobra]

Just to add, using elemental heating values published at Wiki, (

http://en.wikipedia.org/wiki/Heat_of_combustion),

here is what I got earlier.

Using Qlhv = 32.808 and 120.971 MJ/kg for carbon and hydrogen, respectively, I came up with 44.79 and 19.91 MJ/kg for gasoline (approx as C8H15) and methanol (C1H4O1). For stoich mass ratios, I was coming out with 14.609 and 6.473, respectively.

So using those numbers, I get 3.066 and 3.076 MJ/kg_air for gasoline and methanol at stoich. So 0.3% higher. So at least tipping in the same direction as Pat had seen reported.

Per kg of mix, it comes out to 2.87 and 2.664 MJ/kg_mix, which are not too much different than in Heywood's table.

 

[WolfHR]

Yep, I remembered 44.7MJ/kg3 but chose to use his numbers... (but I get 0.88% increase with your numbers- still it's quite a bit of discrepancy to previous 5%)

Now that we've solved the mystery of energy stored in the mixture, another thing is intriguing me. Looking at those numbers, it's apparent that in case of methanol the weight of mixture should be more than twice the weight of gasoline mixture- I wonder how does that affect intake cycle, mixture formation, &c.

 

[Lou Scannon]

You guys are barking up the wrong tree. The power difference of methanol vs gasoline is not due to slight energy density differences in the first approximation of the mass of the captured charge.
It is due to a) the increased charge density due to the increased evaporative cooling of the methanol, b) the ability to configure and tune the engine much more aggressively in terms of manifold pressure, peak cylinder pressure, and heat release rate, without destructive combustion knock (due to the internal cooling effect of fuel evaporation, and methanol's superior antiknock properties), and c) a subtle but positive effect of the specific heat ratio of the charge during compressiom vs that during expansion that favors methanol over gasoline.

 

[black2003cobra]

Yes, it is well known that methanol has laudable anti-knock properties. Its higher chemical octane and superior charge cooling benefits allow for higher compression, closer to MBT timing, and/or higher boost pressures, which of course all served to increase power.

In addition, methanol also has a higher burn velocity. The shorter burn duration results in a more constant-volume like cycle, which improves thermal efficiency. It also tends to reduce MBT timing. And since the end gas is consumed more quickly, there’s less chance of detonation, as a result.

Not only does the higher latent heat of vaporization help prevent knock, but the lower temperatures throughout the cycle also result in less heat loss to the cooling system. This also helps thermal efficiency.

I agree that the difference in cp/cv may be subtle. While I have looked at that for the case of ethanol, I have not done so with ethanol.

There are probably other things I’m forgetting So yes…lots of other effects to consider, other than just the energy content of the fuel, hemi. It's good to mention them.

(Woof woof.)

 

[hydromarine]

Interesting to read patprimmers claim that a magneto is more efficient than a coil ignition system . Speedway bikes which run on methanol fuel and castrol r40 lube oil moved away from the magneto

 

[patprimmer]

But they are normally aspirated I believe and not so hard on the ignition. Electronic will give more control over timing if it has the grunt to fire the charge, however a maggy still reigns where very rich mixture and high boost levels are used.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules