FAI fuel question (Full Version)

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RoNeRiC -> FAI fuel question (8/20/2004 2:29:53 PM)

I'm going to get a new MVVS .49 engine. Needs 0-5% nitro. I bought 0% omega fuel which has 17% lube w/70syn 30 castor. I was reading the instructions and this forum about oil content. I want the total oil content to 20%. I'm looking at this to add to it http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXS622&P=0 . Now how much do I need to add to it to get to 20%, is this stuff ok, and since it is no nitro fuel will it still run ok without adding more methanol?

Another thing, if most engines require at least 18%, then why not make it with at least 18%. Like Omega is 17% oil content. Why 17%? Will not having that 1% be damaging to the engine?



RoNeRiC -> RE: FAI fuel question (8/20/2004 2:36:03 PM)

I was looking at the chart at klotzs website, is 4 oz the right answer, to bring 17% up to 20%? Measurement is for a gallon.



downunder -> RE: FAI fuel question (8/21/2004 1:19:13 AM)

Let me try using these strange American ounces :)
1 gallon is 128 ounces and if the oil is 17% of this then there's 21.76 ounces of oil in there. If the content had been 20% oil then there'd be 25.6 ounces of oil so an extra 4 ounces would be near enough. But if you add 4 ounces then you end up with 132 ounces of fuel in total containing 25.76 (21.76 + 4) ounces of oil which gives 19.5% oil. Yes, I used a calculator to figure this out :)

If you use metrics it goes like this.
1 litre (1000cc) of fuel with 17% oil gives 170cc of oil. With 20% oil there's 200cc of oil so add 30cc and you're close. You don't need a calculator to work this out :)



Ed Smith -> RE: FAI fuel question (8/21/2004 2:32:29 AM)

quote:

I was looking at the chart at klotzs website, is 4 oz the right answer, to bring 17% up to 20%? Measurement is for a gallon.


If the Klotz site says 4 oz why do you doubt it?

I find it rather amusing when people agonise over a 1% difference in oil content for say a $300.00 engine. Parked outside they probably have a$25,000.00 vehicle in which they drive to the sleaziest corner gas bar and fill it with the cheapest gas they can find!!


Ed S



RoNeRiC -> RE: FAI fuel question (8/21/2004 4:01:43 AM)

quote:

ORIGINAL: Ed Smith

quote:

I was looking at the chart at klotzs website, is 4 oz the right answer, to bring 17% up to 20%? Measurement is for a gallon.


If the Klotz site says 4 oz why do you doubt it?

I find it rather amusing when people agonise over a 1% difference in oil content for say a $300.00 engine. Parked outside they probably have a$25,000.00 vehicle in which they drive to the sleaziest corner gas bar and fill it with the cheapest gas they can find!!


Ed S


It doesn't say 4oz, I did the math of what they had on their percentage chart and that is what I came up with. Just wanted to see if I was right. Amazing that people answer threads with no advice at all.



RoNeRiC -> RE: FAI fuel question (8/21/2004 4:05:19 AM)

quote:

ORIGINAL: downunder

Let me try using these strange American ounces :)
1 gallon is 128 ounces and if the oil is 17% of this then there's 21.76 ounces of oil in there. If the content had been 20% oil then there'd be 25.6 ounces of oil so an extra 4 ounces would be near enough. But if you add 4 ounces then you end up with 132 ounces of fuel in total containing 25.76 (21.76 + 4) ounces of oil which gives 19.5% oil. Yes, I used a calculator to figure this out :)

If you use metrics it goes like this.
1 litre (1000cc) of fuel with 17% oil gives 170cc of oil. With 20% oil there's 200cc of oil so add 30cc and you're close. You don't need a calculator to work this out :)


So if I add the 4oz to a gallon of Omega,to bring it from 17% to 20%, will that effect my power output by throwing the percentage of Nitro/ methanol/oil?



Ed Smith -> RE: FAI fuel question (8/21/2004 8:53:00 AM)

Ok, here is some advice. Because you will have reduced the percentage of the ingredient in the fuel that burns there will be a minimal decrease in performance. When I say minimal I mean so small that you will not be able to tell the difference. You would experience a bigger variation on different days of climate changes. Likewise the small amount of oil being added will not make much difference to the lubricating properties of the fuel, which at 17% is quite adequate. I have run high performance racing engines on high nitro fuel with 14% of all synthetic oil with no problems.

MVVS are robust quality built engines, small variations in oil or even other ingredients will make no discernible difference. Whatever fuel you will be using when operating this engine is the fuel you should be using for break-in.

Ed S



RoNeRiC -> RE: FAI fuel question (8/21/2004 5:33:19 PM)

quote:

ORIGINAL: Ed Smith

Ok, here is some advice. Because you will have reduced the percentage of the ingredient in the fuel that burns there will be a minimal decrease in performance. When I say minimal I mean so small that you will not be able to tell the difference. You would experience a bigger variation on different days of climate changes. Likewise the small amount of oil being added will not make much difference to the lubricating properties of the fuel, which at 17% is quite adequate. I have run high performance racing engines on high nitro fuel with 14% of all synthetic oil with no problems.

MVVS are robust quality built engines, small variations in oil or even other ingredients will make no discernible difference. Whatever fuel you will be using when operating this engine is the fuel you should be using for break-in.

Ed S


Thanks Ed. I can't wait until I fire that beast up!!!!



hauckf -> RE: FAI fuel question (8/21/2004 7:04:49 PM)

To raise the oil percentage in a gallon of fuel from 17% to 20% add 4.8 ounces of oil to the gallon. If you want to calculate it yourself, here's the formula:

Fl oz. to add to a gallon = (D% -S%) X 128 / (100 - D%) where D% is the desired oil percentage, S% is the starting oil percentage. In your example, (20 - 17) X 128 / (100 - 20) = 4.8

Here's an easier way: If you are trying to raise the oil percentage of a gallon of fuel to 20% oil, add 1.6 oz. of oil for each percent of increase you want. In your case, you want to increase the percentage from 17 to 20, or 3%. 3 X 1.6 = 4.8 oz.

To get to 18% add 1.56 oz for each % increase you want.
To get to 19% add 1.58 oz for each % increase.
To get to 21% add 1.62 oz for each % increase.
To get to 22% add 1.64 oz for each % increase.

If you don't want to do any math at all, there are several sites that have calculators that will do the math for you, and several programs to do the calculations have been offered on this forum. (Sorry, I don't have any of the addressed for the sites.)



downunder -> RE: FAI fuel question (8/22/2004 1:29:08 AM)

quote:

ORIGINAL: RoNeRiC
So if I add the 4oz to a gallon of Omega,to bring it from 17% to 20%, will that effect my power output by throwing the percentage of Nitro/ methanol/oil?

Adding some oil won't affect the power at all. The "fuel" part of fuel is just the methanol/nitro and the flow rate of this is what's set by the needle valve. If you add some oil then the needle just needs to be opened very slightly more (because now you're flowing slightly more oil) to get back to the same rate of methanol/nitro.



kostask -> RE: FAI fuel question (9/19/2004 11:24:27 PM)

QUESTION:
ACCORDING TO KYOSHO THE STANDARD FUEL FOR THEIR STADIUM FORCE TRUCK IS 10% NITRO AND THE HIGH PERFORMANCE IS 16%,NOW I ASKED AT THE PLACE WHERE I BOUGHT MY R/C IF IT' S BETTER TO RUN THE TRUCK WITH FUEL HAVING 10% NITRO SO TO KEEP IT COOLER EVEN THOUGH IT WON'T BE AS FAST,AND THEY TOLD ME THAT THE MORE NITRO IN THE FUEL THE COLDER IT RUNS ... THAT DOESN 'T SEEM RIGHT THOUGH....A FRIEND TOLD ME THAT HE HAD BOUGHT BRAKE IN FUEL WHICH HAD NO NITRO IN IT AND THE ENGINE USED TO RUN REAL SWEAT..SO,ANYBODY HAVE ANY IDEA ABOUT THAT?
THANK YOU FOR YOUR TIME!



Jim Schwagle -> RE: FAI fuel question (9/24/2004 11:47:43 PM)

The higher the nitro content, the richer you need to run the engine, to get enough fuel for the air passing through the carb (higher nitro means less methanol per ounce of fuel). More fuel means more oil, leads to a little cooler running engine.



Bax -> RE: FAI fuel question (9/29/2004 10:26:08 PM)

quote:

ORIGINAL: Jim Schwagle

The higher the nitro content, the richer you need to run the engine, to get enough fuel for the air passing through the carb (higher nitro means less methanol per ounce of fuel). More fuel means more oil, leads to a little cooler running engine.


Sorry, but I must disagree. More power = more heat. No way to get around that. The actual needle setting will change, but if you're getting a higher power output, the engine will run at a higher temperature.



sdavied -> RE: FAI fuel question (10/13/2004 6:44:21 PM)

For any mathematicians out there, here is the derivation of the equation:

x = amount to add
S = (% oil in original fuel) / 100
D = (% oil desired) / 100
Ts = Total volume at start
Te = Total volume at end
(note: x and T must be in the same units of measure)

Te = Ts + x
Ts * S = volume of oil at start
Te * D = volume of oil at end

TeD = TsS + x
(Ts + x)D = TsS + x
DTs + Dx = TsS + x
DTs - TsS = x - Dx
DTs - TsS = x(1 - D)

[Ts(D - S)] / (1 - D)

This works with any system of measure (metric or US).



Jim Schwagle -> RE: FAI fuel question (10/16/2004 8:44:21 PM)

All I can do is repeat what Dave Shadel said. With a higher nitro fuel, you richen it up, power output is similar, but with a richer mixture, you run cooler. Perhaps we are talking about two different things. With higher nitro, you run richer than normally. Yes, more nitro adds heat to the engine, but more oil helps remove it. I guess it just depends upon if you are trying to lean it for every RPM. Heli pilots will run on 30% fuel, but with 23% oil and I've seen the head cool enough to put your fingers on, but Helis tend to run richer than "plankers". It's all determined by where you leave that little old needle.

Edit for clarity.
Second edit for grammar....duh.



kostask -> RE: FAI fuel question (10/18/2004 9:38:16 PM)

So the main factor of cooling for the two stroke nitro-methanol engines is the amount of oil in the fuel?I thought it was methanol as it evaporates like alchohol..in that case,my thinking was all wrong from the start.But with Helis i don't think heat sould be a problem since i guess the engine gets cooled by the propeler "excuse my english" ,although i wouldn'd say i know anything about helis yet.But i think there's a big difference when you want to talk about a nitro truck witch needs to run like hell to get the engine cool down..
Still trying to figer things out though so i'm sorry if i 'm being wrong.
Thank you all for your time!



downunder -> RE: FAI fuel question (10/19/2004 2:30:40 AM)

kostask
You were correct with what you first thought. A great deal of the cooling comes from the evaporation of the methanol and nitro inside the engine. Nitro has a much lower latent heat of evaporation than methanol but because so much nitro has to be mixed with the air to get the correct mixture the increased mass can absorb more heat. With a very rich mixture a lot of the fuel is still being vaporised when it gets up into the cylinder and that helps cool the engine even more, to the point where it's possible to run an engine without a prop and it won't overheat.

The oil does virtually nothing as far as carrying heat out of the engine. Every cycle there's only a miniscule amount of oil going in which means that there's also only a miniscule amount going out the exhaust each cycle. The oil doesn't come out as a vapor (hopefully) so all that happens to it is it gets a little hotter. This absorbs (and carries away) an insignificant amount of the total heat.



Jim Schwagle -> RE: FAI fuel question (10/19/2004 4:11:52 PM)

Well, the whole discussion interested me, in that I'm sure many of my preconceived ideas are wrong, but upon thinking it occurred to me that the amount of oil involved was so small that it shouldn't have a big impact, as long as the engine was adequately lubricated. So...I thought I'd dig up the 'ol chem book and see. In the end, all it gave me was enough facts to tell me I still had no idea...

I assumed 34g of methanol (1 mole) and 20% oil, Castor Oil, simply because I found them first. I'm sure Nitro changes it somewhat.

Heat of combustion of 34g of methanol ...... 726,000 Joules


Heat absorbed by 8.5g of Castor Oil going up 200C....4800 Joules

Heat absorbed by 34g of methanol going up 100C is 8500Joules.
Heat absorbed by 34g of methanol vaporizing 38000J


All this was done on the fly, the numbers assume starting at around room temp and your mileage may vary, I hope the numbers are correct, no calculator handy (on this computer). Not all of the heat is absorbed by the engine since the exhaust contains, I would bet, a substantial amount of heat. (50%, 30% ??? I don't know, didn't estimate)

All it seems to tell me is that these things we've talked about seem to account for less than 10% of the heat produced. I guess air does most of the work, or does it go out the exhaust?. I suppose someone more knowledgeable can explain.

Edit for clarification.
2nd Edit for grammar...duh.



SoonerAce -> RE: FAI fuel question (10/21/2004 8:27:05 AM)

[X(]Just a "just in case your new" note. I found this while reading the Klotz syth oil tech notes:

COMMENTS: Do not use in oil injection systems
This will not blend with petroleum-based oil
Do not use as a storage lubricant
Also available the Original Techniplate KSFP0200

So if you have a fuel with petro base oil in it (two-stroke oil), ya best not put this with it. lest you like gumballs in your fuel system.[:D]



Bax -> RE: FAI fuel question (10/26/2004 11:00:22 PM)

Jim,

If you limit your power when you up the nitro, your engine may run cooler because you're not using all the fuel that goes into the engine. If you're leaning to peak RPM, you'll have a higher RPM level than with the lower nitro. That's caused by higher combustion pressures, and that means more heat is being generated.

My charts are old, so they're in pounds and BTU, but:

Nitro combustion releases 5,000 BTU/pound of air X Fuel/Air ratio of .58 = 2,900 BTU released/pound of air
Methanol combustion releases 9,600 BTU/pound of air X Fuel/Air ratio of .22 = 2,112 BTU released/pound of air

With higher RPM, you get more air flowing through the engine (it is a pump, after all) per unit of time. More air = more fuel burned. More fuel burned = greater heat energy released per unit of time. Since nitro flows more heat per unit of time, than does methanol, increasing the nitro will increase the heat flow. This assumes that the engine is leaned to peak power, which would be close to the best fuel/air ratio of the fuel mixture.

Nitro also has a lower latent heat of vaporization than methanol, so any cooling effect from fuel vaprization is reduced when nitro content in increased.

Bottom line is that if you're drawing more power out of the engine, more heat is developed. With some installations, the engine runs cooler to the touch because there may be a more efficient cooling system. Helis generally have larger cylinder heads as well as cooling fans. The airflow is restrained to flow around the engine and through the fins. This means the system's more efficent, so the overall cooling is better, and the engine's temp at any one point may be lower. With a different cooling system, temps will be measurably higher, yet an engine's still running perfectly well.



Sport_Pilot -> RE: FAI fuel question (10/27/2004 3:17:32 AM)

Bax,
I agree with most of what you are saying. Buy heat is not the same thing as temperature. Both nitro and methanol will generate more heat than gasoline when run at peak lean, yet have a lower temperature. Heat is the transfer of molecular kinetic energy, temperature is the measurement of the molecular activity (how much the molecules are bouncing against each other). When the temperature is raised from one temperature to another you have heat. A diffeance of 70 to 300 degrees is the same heat as from 20 to 250 degrees. Methanol and nitro engines get their power from a higher mass flow, not higher temperature nor heat. Still as you say nitro will generate a higher temperature than methanol at peak lean. However I run high nitro at 300 to 600 RPM's rich. When run rich nitro will run at about the same temperature as methanol, or if run slightly richer it will run slightly cooler and still develop more power. But watch out for the lean runs, especially if it detonates when lean. You can run an engine in a hurry with a lean run on nitro.



Red B. -> RE: FAI fuel question (10/27/2004 10:19:04 AM)

Here is a simple fuel mixture spreadsheet thet will handle the math.
Right click on the seemingly broken picture and do "Save target as". Name the file "homebrewer.xls", then open it up using MS Excel.

BTW, a couple of percent up or down doesn't matter much for a sport glow engine. Running lean is what usually kills the engine.

/Red B.



Bax -> RE: FAI fuel question (10/27/2004 3:43:03 PM)

Sport Pilot,

You're correct about running richer. If you went from 15% ntitro to 30% nitro but limited the engine to the performance of the 15% nitro, then the engine will run cooler. It's just that for most people, this isn't done. People go up in nitro to get more power and lean the engine to just rich of peak RPM, just enough so that the engine doesn't go overlean when the engine unloads and the fuel level in the tank drops. The engine will run hotter.



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