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Old Apr 18, 2007, 11:24 AM
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Wouldn't more nitro allow an engine to run cooler?

I am wondering why people say if an engine is running hot, to try lower nitro? When racing drag bikes, and setting the engines up that we ran nitrous thru, we had to use a hotter thermostat because once the nitrous kicked in it would cool the engines down big time. I was always under the impression it was because the fuel burn was more of an instant explosion, and not a long drawn out fuel burn.

I am completely neutral about this, so I am just wanting to hear everyones opinions.

As a test I bought 4 different brews of fuel Omega 5%, Omega 10% Cool power 20% and Cool power 30%Heli. I typically run 15% CP, but have a Magnum 1.08 that was running hot, and was told to try lower nitro, which made me want to do this test.

I actually found the engine to run the coolest on the CP 30%Heli with a head temp of 189 degrees, and the hottest on the Omega 10% at 215 degrees. All runs had the High speed peaked, then backed off 300 rpm.

I am sure my test was highly inconclusive, but I found it interesting anyways.

Mike.
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Old Apr 18, 2007, 11:49 AM
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Quote:
Originally Posted by mtwister
I am wondering why people say if an engine is running hot, to try lower nitro? When racing drag bikes, and setting the engines up that we ran nitrous thru, we had to use a hotter thermostat because once the nitrous kicked in it would cool the engines down big time. I was always under the impression it was because the fuel burn was more of an instant explosion, and not a long drawn out fuel burn.

I am completely neutral about this, so I am just wanting to hear everyones opinions.

As a test I bought 4 different brews of fuel Omega 5%, Omega 10% Cool power 20% and Cool power 30%Heli. I typically run 15% CP, but have a Magnum 1.08 that was running hot, and was told to try lower nitro, which made me want to do this test.

I actually found the engine to run the coolest on the CP 30%Heli with a head temp of 189 degrees, and the hottest on the Omega 10% at 215 degrees. All runs had the High speed peaked, then backed off 300 rpm.

I am sure my test was highly inconclusive, but I found it interesting anyways.

Mike.
First thing's first... Nitro methane and Nitrous oxide are two totally different things. Nitro Methane is a fuel, that is extremely explosive, while Nitrous oxide is an inflammable gas. It is used for the sole purpose of increasing the oxygen content, per volume of gas. At somewhere aroun 530 degrees, the N20 (nitrous) separates into it's components and allows for higher oxygen levels,a nd in turn, greater fuel consumption, producing more horsepower. One reaosn why nitrous allows the engine to run cooler is that the nitrous is compressed. When a compressed substance is expanded, it absorbs heat, making it cool. It is the same way that if you touch a bottle after using it (right after), the bottle will be cold. So the nitrous in in fact lowering the air intake temperature, therefor lowering the temperature of the engine, especially on forced induction engines.

Honestly, I couldn't tell you why lower nitro methane contents burns cooler. I am not sure what the A/F ratios are for nitro and methanol, but that may have something to do with it. Also, you are putting out lower horsepower with lower nitro, and it is a general rule of thumb that the harder you stress and engine, the hotter it is going to get.

I hope that at least helps a little bit in answering your question.

Scott
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Old Apr 18, 2007, 12:29 PM
Zor
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Quote:
Originally Posted by mtwister
I am wondering why people say if an engine is running hot, to try lower nitro? When racing drag bikes, and setting the engines up that we ran nitrous thru, we had to use a hotter thermostat because once the nitrous kicked in it would cool the engines down big time. I was always under the impression it was because the fuel burn was more of an instant explosion, and not a long drawn out fuel burn.

I am completely neutral about this, so I am just wanting to hear everyones opinions.

As a test I bought 4 different brews of fuel Omega 5%, Omega 10% Cool power 20% and Cool power 30%Heli. I typically run 15% CP, but have a Magnum 1.08 that was running hot, and was told to try lower nitro, which made me want to do this test.

I actually found the engine to run the coolest on the CP 30%Heli with a head temp of 189 degrees, and the hottest on the Omega 10% at 215 degrees. All runs had the High speed peaked, then backed off 300 rpm.

I am sure my test was highly inconclusive, but I found it interesting anyways.

Mike.

http://en.wikipedia.org/wiki/Nitromethane
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Old Apr 18, 2007, 12:47 PM
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Well, going by the link you provided, it shows this ......

Nitromethane has a laminar combustion velocity of approx. 0.5 m/s, somewhat higher than gasoline, thus making nitromethane suitable for high speed engines. It also has a somewhat higher flame temperature of about 2400 C. The high heat of vaporisation of 0.56 MJ/kg together with the high fuel flow provides significant cooling of the incoming charge (about twice that of methanol), resulting in reasonably low temperatures. In a Top Fuel drag racing engine this alone will provide the cooling of the engine, as the cylinder heads are machined from solid pieces of aluminum billet with no water jackets.
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Old Apr 18, 2007, 01:09 PM
Zor
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Quote:
Originally Posted by mtwister
Well, going by the link you provided, it shows this ......

Nitromethane has a laminar combustion velocity of approx. 0.5 m/s, somewhat higher than gasoline, thus making nitromethane suitable for high speed engines. It also has a somewhat higher flame temperature of about 2400 C. The high heat of vaporisation of 0.56 MJ/kg together with the high fuel flow provides significant cooling of the incoming charge (about twice that of methanol), resulting in reasonably low temperatures. In a Top Fuel drag racing engine this alone will provide the cooling of the engine, as the cylinder heads are machined from solid pieces of aluminum billet with no water jackets.

Well said mtwister

Then we can consider how nitromethane increase the power developped by an engine.
The chemical formula provides readily available oxygen.
Without nitro all the oxygen to burn the methanol (wood alcool) comes from the air sucked into the carburetor and only about 20% of the air is oxygen.

With nitro the fuel is itself carrying in some of the oxygen so we have more efficient burning, higher pressure pushing down the piston, cleaner exhaust (the lubricant castor oil or synthetic is still there of course).

Results is higher RPM and higher torque that reaults in higher Horse Power.

It all makes sense, doesn't it ?

My usual best regards to you,

Zor
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Old Apr 18, 2007, 01:14 PM
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Yes, absolutely, and what makes more sense is the fact that nitro does bring more oxygen in, thus more nitro does in fact cool an engine, not cause it to run hotter. This would make my sample test understandable to me now. Thanks for the link Zor, it's very useful..

Mike.
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Old Apr 18, 2007, 01:16 PM
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I do understand that their chemical compounds are different, but their intended purposes are identical. Both raise combustion chamber pressures, both charge the incoming air thus cooling it etc...


Quote:
Originally Posted by sdueck
First thing's first... Nitro methane and Nitrous oxide are two totally different things. Nitro Methane is a fuel, that is extremely explosive, while Nitrous oxide is an inflammable gas. It is used for the sole purpose of increasing the oxygen content, per volume of gas. At somewhere aroun 530 degrees, the N20 (nitrous) separates into it's components and allows for higher oxygen levels,a nd in turn, greater fuel consumption, producing more horsepower. One reaosn why nitrous allows the engine to run cooler is that the nitrous is compressed. When a compressed substance is expanded, it absorbs heat, making it cool. It is the same way that if you touch a bottle after using it (right after), the bottle will be cold. So the nitrous in in fact lowering the air intake temperature, therefor lowering the temperature of the engine, especially on forced induction engines.

Honestly, I couldn't tell you why lower nitro methane contents burns cooler. I am not sure what the A/F ratios are for nitro and methanol, but that may have something to do with it. Also, you are putting out lower horsepower with lower nitro, and it is a general rule of thumb that the harder you stress and engine, the hotter it is going to get.

I hope that at least helps a little bit in answering your question.

Scott
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Old Apr 18, 2007, 11:13 PM
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There's something of a balancing act going on with the fuels we use and the way the engine is cooled. The engine gets cooled in two ways, internally by using latent heat of evaporation and externally through the cooling fins. The heat gets generated by the power available (actually by the wasted power). Obviously the external area for cooling is fixed so at first glance it would seem that more (wasted) power means more heat. That's likely where the advice to use lower nitro came from.

Methanol has a huge ability to draw heat as it evaporates, it's almost twice as good as nitro, and because it gives slightly less power than a nitro blend then it could be assumed to run a little cooler.

But here's the complication. For best power (not stoichiometric) methanol burns at an air/fuel ratio between 4.5 and 6.5:1 while nitro begins (it's leanest) at 2.5:1 or twice as rich as methanol. Now seeing that nitro is being used twice as fast as methanol but is only half as good at absorbing heat internally it averages out at the same as methanol. But this is for it's leanest setting. It can easily handle an air/fuel ratio of 0.5:1 which is 5 times richer so the fuel flow is massive and can absorb a considerable amount of heat. Is it any wonder that nitro makes finding a good needle setting much easier?

So the end result is that, although the engine is delivering more power to waste through heat, the fuel is cooling internally at a quite high rate which relieves the load on the cooling fins. In practise there'll be little difference in head temps with whatever fuel is used.
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Old Apr 18, 2007, 11:54 PM
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Did you check the oil content of the different fuels. Higher oil content will increase lubrication less friction...less heat.
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Old Apr 19, 2007, 01:13 AM
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Originally Posted by Lightnin
Did you check the oil content of the different fuels. Higher oil content will increase lubrication less friction...less heat.
Yes, they were all 17%
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Old Apr 19, 2007, 03:10 AM
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Quote:
Originally Posted by mtwister
I do understand that their chemical compounds are different, but their intended purposes are identical. Both raise combustion chamber pressures, both charge the incoming air thus cooling it etc...
I do not agree with this. Yes, they have similar effects, but they are not for the smae intended purpose. They both produce significantly higher horsepower, but an engine, assuming it is built right, can run on straight nitro, while if you inject nitrous without fuel, you will have a heck of a time sitting still... The only thing it can do on it's own is make pulling teeth a bit less of a pain. Once again, nitro is a fuel, and nitrous is not. Nitrous is not at all flamable. There is nothing about it that screams flamable. It only allows for higher oxygen levels, allowing for greater fuel consumption, but it does not burn... Whereas nitro does burn... And the fact that you can cram so much more fuel in (due to the above stated A/F ratio) and that it burns faster, you can get higher power out of it. There are other factors too, but we won't go there. Essentially all I am saying is that nitrous is for the intended purpose of adding oxygen to a car's intake, while nitro is a fuel that is meant to produce power. It is in fact more combustible than methanol, ethonal, and especially gasoline. The aspect of cooling brings up another argument, but I won't go there other than say that if anyone out there plays paintball like I do, they know full well that if you fill a CO2 tank wrong, and release too much gas too fast, or shoot too fast, your tank gets cold... real cold. Evaporation is what is making the cooling take place, along with the rapid expansion of a substance that is typically a gas at room temperature, but it is happening on much higher levels than the nitro being introduced in the engine. Nitro is not compressed into a liquid, but nitrous is.

Scott
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Old Apr 19, 2007, 11:19 AM
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For the most part, I agree with what you're saying. But, as far as your cylinders getting cold, due to evaporation is wrong. Take an a/c system in your car for example. It actually super heats the refrigerant to a high pressure, and a very high temp, then, it send this high temp, high pressure liquid thru an orifice, and into a less pressurized state. This change in pressure, is what allows the super heat exchange to take place, instantly cooling the refrigerant and creating condensation, and sometimes ice on the lower pressure side of the a/c system. It's the same thing your co2 bottles are doing in paintball. It's called super heating. Also, it is the fact, that BOTH nitroM and nitrous PULL more oxygen into the sytem, that makes me say their theory of operation is similar.



Quote:
Originally Posted by sdueck
I do not agree with this. Yes, they have similar effects, but they are not for the smae intended purpose. They both produce significantly higher horsepower, but an engine, assuming it is built right, can run on straight nitro, while if you inject nitrous without fuel, you will have a heck of a time sitting still... The only thing it can do on it's own is make pulling teeth a bit less of a pain. Once again, nitro is a fuel, and nitrous is not. Nitrous is not at all flamable. There is nothing about it that screams flamable. It only allows for higher oxygen levels, allowing for greater fuel consumption, but it does not burn... Whereas nitro does burn... And the fact that you can cram so much more fuel in (due to the above stated A/F ratio) and that it burns faster, you can get higher power out of it. There are other factors too, but we won't go there. Essentially all I am saying is that nitrous is for the intended purpose of adding oxygen to a car's intake, while nitro is a fuel that is meant to produce power. It is in fact more combustible than methanol, ethonal, and especially gasoline. The aspect of cooling brings up another argument, but I won't go there other than say that if anyone out there plays paintball like I do, they know full well that if you fill a CO2 tank wrong, and release too much gas too fast, or shoot too fast, your tank gets cold... real cold. Evaporation is what is making the cooling take place, along with the rapid expansion of a substance that is typically a gas at room temperature, but it is happening on much higher levels than the nitro being introduced in the engine. Nitro is not compressed into a liquid, but nitrous is.

Scott
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Old Apr 19, 2007, 11:58 AM
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Quote:
Originally Posted by mtwister
Yes, absolutely, and what makes more sense is the fact that nitro does bring more oxygen in, thus more nitro does in fact cool an engine, not cause it to run hotter. This would make my sample test understandable to me now. Thanks for the link Zor, it's very useful..

Mike.
Huh? More consumable oxygen results in more combustion = more heat. Ergo, lower Nitromethane in the fuel, the cooler the engine runs. It does not run as fast nor does it produce as much power with lower methane. More nitromethane will not cool your engine.

The nitromethane is added to improve combustion not to cool engines. Improved combustion results in higher operating temperatures given all things being equal (Thermo dynamics). More alcohol is burned so the heat has got to go up not down.

Different story with Nitrous Oxide.

Cheers,

Chip
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Old Apr 19, 2007, 12:38 PM
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Quote:
Originally Posted by mtwister
... Take an a/c system in your car for example. It actually super heats the refrigerant to a high pressure, and a very high temp, then, it send this high temp, high pressure liquid thru an orifice, and into a less pressurized state. This change in pressure, is what allows the super heat exchange to take place, instantly cooling the refrigerant and creating condensation, and sometimes ice on the lower pressure side of the a/c system. It's the same thing your co2 bottles are doing in paintball. It's called super heating. ...
Not true. If that was the case there will be no cooling effect whatsoever - refrigerant at ambient temp. when pressurized will get hot and if expanded while still hot it will come back to ambient temp (almost), so there will be no cooling. In an AC system the pressurized and hot refrigerant is fed to a cooler (usually right behind the engine radiator) where it cools down to ambient temp (almost). When expanded, the refrigerant drops its temperature and as it enters the orifice at ambient temp, the resulting temperature is lower than ambient.

Back to nitromethane - an engine running on pure nitromethane will have less power than running on pure methanol. The reason is that nitromethane produces much less energy when it burns than methanol. There's an optimum nitromethane and methanol mix which produces max. energy. It usually depends on engine design. Nitromethane mixed with methanol has the same effect as nitrous oxide in gasoline engines by providing more free oxygen in the combustion chamber thus allowing more fuel to burn (richer fuel/air mixture) which in turn makes more power.

Ivan
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Old Apr 19, 2007, 01:07 PM
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The cooler is exactly right, it drops the pressure and the heat instantly.

Quote:
Originally Posted by ivanc
Not true. If that was the case there will be no cooling effect whatsoever - refrigerant at ambient temp. when pressurized will get hot and if expanded while still hot it will come back to ambient temp (almost), so there will be no cooling. In an AC system the pressurized and hot refrigerant is fed to a cooler (usually right behind the engine radiator) where it cools down to ambient temp (almost). When expanded, the refrigerant drops its temperature and as it enters the orifice at ambient temp, the resulting temperature is lower than ambient.

Back to nitromethane - an engine running on pure nitromethane will have less power than running on pure methanol. The reason is that nitromethane produces much less energy when it burns than methanol. There's an optimum nitromethane and methanol mix which produces max. energy. It usually depends on engine design. Nitromethane mixed with methanol has the same effect as nitrous oxide in gasoline engines by providing more free oxygen in the combustion chamber thus allowing more fuel to burn (richer fuel/air mixture) which in turn makes more power.

Ivan
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