 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
| HomeDiscussion Groups General ModelsRailroadsRocketsRadio Controlled Air ModelsHelicoptersLand ModelsWater ModelsModelGeeks.com Contact UsLink To UsSearch & Site Map |
Model Forum / Radio Controlled / Land Models / April 2005which fuel?
what is the differance between 16% and 25% nitro fuel?? apart from the 25% being more combustable which has the better lubricating quality?? > what is the differance between 16% and 25% nitro fuel?? > apart from the 25% being more combustable which has the better lubricating > quality?? The "25%" is 25% nitro by volume, if I recall correctly. Intuitively, less nitro means more lubricant...shouldn't it? If you don't care about rebuilding your engines because you compete on a regular basis, use 25%...or higher. If you're a Sunday flyer, use 10-15% and let your engines last longer. At least, that was my rule of thumb. For 2-cycle engines. May be out-moded thinking for a 4-stroke.  Signature- Rufus > > what is the differance between 16% and 25% nitro fuel?? > > apart from the 25% being more combustable which has the better lubricating [quoted text clipped - 7 lines] > 10-15% and let your engines last longer. At least, that was my rule of > thumb. For 2-cycle engines. May be out-moded thinking for a 4-stroke. hi rufus thats what i thought, but was not sure,, i wonder what else they put in the fuel as i cant see that 25% mix would be 25% nitro and the other 75% being oil,,, but there again i have been wrong before :( 25% nitro ,70% Menthanol , 5% oil..... the 10% nitro is kindest to your 2 stroke...pj >> > what is the differance between 16% and 25% nitro fuel?? >> > apart from the 25% being more combustable which has the better [quoted text clipped - 15 lines] > 25% nitro and the other 75% being oil,,, > but there again i have been wrong before :( > 25% nitro ,70% Menthanol , 5% oil..... the 10% nitro is kindest to your 2 > stroke...pj thanks pj so you recomend the lets say 10% to 16% for my old suzuki GT250 then lol ;) no seriosly though getting back to the subject in hand..... any idea the fuel to air mixture that is created in the carb?? i know on a normal petrol engine the mixture is 16 parts air to one part fuel.. but on a nitro model i have no idea but would love to find out more ... >> 25% nitro ,70% Menthanol , 5% oil..... the 10% nitro is kindest to your > 2 [quoted text clipped - 11 lines] > > but on a nitro model i have no idea but would love to find out more ... also the compresion ratio and port timing are a factor in the amount of nitro that an engine will happily run on I'm not convinced that nitro content up to about 30% has any shortening effect on motor life. I reckon that with 30% they start easier, make more power, idle better and actually run a little cooler. I think the supposed engine wear is only due to people not resetting their tune when they up the nitro content. Personally I think there is nothing to be gained by sticking under 25 - 30%. MIKE >> what is the differance between 16% and 25% nitro fuel?? >> apart from the 25% being more combustable which has the better [quoted text clipped - 8 lines] > and let your engines last longer. At least, that was my rule of thumb. > For 2-cycle engines. May be out-moded thinking for a 4-stroke. That may be true for a four-stroker, but not a 2-cycle, I think. The whole point of boosting the nitro content is to affect the thermodynamic cycle - "all heat engines operating between the same temperature difference have the same thermal efficiency", to quote the laws of thermodnamics - by increasing the combustion temperature. A four cycle motor may see less thermal wear because it "rests" during alternate strokes. But a 2-cycle fire on every stroke, and is therefore going to see more increased thermal exposure. Yes - they may start easier because of the increase in the effective thermal content of the combustion mixture. Which can also break down the lubricant...which is one reason I prefer synthetic fuels. And consider anything over about 15% nitro excessive for sport flying with a 2-cycle engine...I don't own any four strokes. I can make up the difference with pressure delivery and a proper (read open and sometimes loud...) exaust system. And what really causes the wear and tear is heating up and cooling down - this is called thermal fatige. Biggest wear factor in a jet engine that I know of...if the engine runs at one constant temprature it will actually fatigue less. SO - the lesson is to consider how you will use your engine and choose a suitable fuel for your purpose. Signature- Rufus > I'm not convinced that nitro content up to about 30% has any shortening > effect on motor life. I reckon that with 30% they start easier, make more [quoted text clipped - 17 lines] >>and let your engines last longer. At least, that was my rule of thumb. >>For 2-cycle engines. May be out-moded thinking for a 4-stroke. um, guys, nitro does not increase the combustion temperature, it produces more reaction gases after the combustion process. What cause the increased wear is the increase in horsepower, which increases the forces on the surfaces of cylinder/bearings etc as you have already learned with sandpaper, the harder you push the more you wear away. > um, guys, nitro does not increase the combustion temperature, it produces > more reaction gases after the combustion process. > What cause the increased wear is the increase in horsepower, which increases > the forces on the surfaces of cylinder/bearings etc > as you have already learned with sandpaper, the harder you push the more you > wear away. Yeah - PV=mRT...can't get around it. Given that everything is constant on the right side of the equation but temperature, there has to be some accompanying elevation in the gas temperature along with increase in pressure/volume caused by the mixture burning more "efficiently". Getting back to my thermodynamic law concerning heat engines - "all heat engines operating between the same temperature difference have the same thermal efficiency" (you can look it up) - what you are doing by adding nitro to the mixture is altering the cycle by increasing the thermal differential. You are adding heat. But in the end you get both - increased heat of combustion, and increased friction heating due to the rise in HP. The fact that the bearings, shaft, and case materials all have differing coeficients of thermal expansion only further aggravates the situation. One way around the increase in the heat of combustion is to add water - note that many WWII fighter engines and a few race cars are water+nitro injected. The water cools the mixture AND adds mass - producing even more HP. Though it can beat the snot out of your pistons...so piston fighter engines usually had a "combat" rating for the use of such systems - placarded to some number of minutes of continuous operation at a given RPM with injection. Signature- Rufus the problem there is that n is increaced by the addition of the nitro it also absorbs the heat generated by combustion to do the cracking of its base elements hence the temperature never ever raises > the problem there is that n is increaced by the addition of the nitro > it also absorbs the heat generated by combustion to do the cracking of its > base elements hence the temperature never ever raises No it isn't. Can't be without violating the law of Conservation of Mass. The entire mass of the fuel air mixture remains constant unless you inject an extra substance - like in the case of the water injection systems I mentioned. The mass flow (and therefore mass, and number of molecules) into (and out of) the cylinder remains constant...unless you have an anti-matter engine and are creating and destroying mass... The swept volume of the cylinder is also constant. It is the pressure that is increased by the addition of heat introduced by the more volatile nitro - it's just simple chemistry...nitro has a higher specific heat coeficeint than plain castor oil...or whatever the base substance of the fuel mixture may be. A higher "energy density", as I've heard it referred to by petrochemists. All fuel additives claiming to increae HP output are really only a way to increase the engergy density of the fuel. By adding heat to the thermal cycle. Signature- Rufus Ahh yes, conservation of mass, but my little friend you forget that the number or reactant chemicals on one side of your equation do not equal the number of product chemicals on the other side. The combustion process breaks down a hugely complex compound on one side eg C12H6 that 1 mole occupies 24l into 12C02 3H2O occupying 360l. And then if you start adding nitromethane etc to the mix the expansion ratio get even greater than just that simple fuel. The mass is conserved but it is just changed in its form. ALL gasses occupy the same 24l/mole regardless of molecular weight. P.S. the ethanol you are using in your fuel contains 5-15% water anyway, so you are already using water injection. 1cc of Water @ 99deg is 1.02 l of steam @ 101 deg...That is half of the water injection system, the other half is that it works as an intercooler on high boost motors. > Ahh yes, conservation of mass, but my little friend you forget that the > number or reactant chemicals on one side of your equation do not equal the [quoted text clipped - 13 lines] > water injection system, the other half is that it works as an intercooler on > high boost motors. I still contend that there is NO WAY you are going to increase the mass of the gas mixture in the cylinder - the number of molecules has nothing to do with affecting the mechanical operation; the mass does (which is why I specifically cited the Perfect Gas law expressed as PV=mRT, and NOT PV=nRT). You may change the chemical combinations, you may change the number of molecules but you are NOT going to create matter in the process of creating pressure. Period. You've said it yourself - "the mass is conserved but it is just changed in it's form". All you can do is add heat. That's the only way to alter the thermodynamics of the cycle. Yes - I agree that the expansion ratio is higher...but that is simply due to the increase in energy content (in the form of heat) of the mixture added by the nitro. Not because the nitro adds any mass. In fact, I'd guess that the specific gravity of nitro is the least of any of the components of the fuel mixture (other than the air involved) and so the higher the nitro content, the lower the specific gravity of the fuel will be, and thus the lower the mass of the fuel will be - again, just guessing...haven't looked it up. But that is a good combination for an aircraft...less weight, more energy available. And no - you are NOT using water injection. Water produced as a by-product of combustion doesn't count. A true water injection system injects liquid H2O directly into the combustion chamber from a seperate container via a seperate and distinct injector. The Roll Royce Pegasus engine has such a system, as well as a few other jet engines I can think of...and some drag racers...to leave out WWII piston fighter engines which employed the scheme. And an intercooler is an entirely different device used to cool compressed turbine exhaust air prior to entering the intake...thus increasing the density (mass) of air introduced to the combustion chamber. Signature- Rufus your formula does not work, it is dependant on the number of moles of molecules not the mass, I am not creating matter/mass, i was pointing out that the density of the byproducts is less than the density of the reactants, and there is more products than reactants. The water i was referring to with the water injection is in the form of impuritys in the ethanol part of the fuel, ethanol is hygroscopic and also breaks down into water and a few other chemicals by itself,,,,perhaps you have seen "stale" fuel? > your formula does not work, it is dependant on the number of moles of > molecules not the mass, [quoted text clipped - 5 lines] > breaks down into water and a few other chemicals by itself,,,,perhaps you > have seen "stale" fuel? Yes - but that is not "water injection" in the engineering/design sense - more like "water embedment"...which doesn't count in the thermodynamic sence, because it is accounted for in the original (intake) mass balance. A true water injection system introduces liquid water directly into either the intake manifold, or during/post combustion - as I have previously stated. And yes - my equation does work. The Perfect Gas law may be stated as PV=mRT; where m is mass, PV=nRT; where n is the number of molocules, or PV=(rho)RT, where (rho) is density. In each case, the units of R change accordingly. That and the 1st and 2nd laws are basic engineering thermodynamic expressions. What is of engineering import in the case of a piston engine (or any mechanical air-breathing engine) is that it is essentially a mass flow system - not a molecular generator. All internal combustion engines are heat engines, in the thermoduynamic sense. Differentiating my initial citation of PV=mRT does work - deltaPV=mR deltaT. V - the swept volume of the cylinder is constant, as are m and R. Therefore, deltaP is proportional to deltaT. Q.E.D. Basic thermo. Even though the density of the products is less than the density of the reactants (which is the case as you point out - and where the increased pressure arrises from) the mass involved is still the same. Hence it is simpler (and more applicable) in the design of such an engine to work with the Perfect Gas law as PV=mRT. Signature- Rufus > reactants (which is the case as you point out - and where the increased > pressure arrises from) the mass involved is still the same. Hence it is > simpler (and more applicable) in the design of such an engine to work > with the Perfect Gas law as PV=mRT. There are relevant posting in rec.models.rc.water Re: what is the differance between 16% and 25% nitro fuel?? > um, guys, nitro does not increase the combustion temperature, it produces > more reaction gases after the combustion process. > What cause the increased wear is the increase in horsepower, which increases > the forces on the surfaces of cylinder/bearings etc > as you have already learned with sandpaper, the harder you push the more you > wear away. and thus can cause more temperture?? any way ANNONUSER what you just said ring true to me, and has always been my learning of it.. but maybe with nitro it runs cooler because the engine runs with less strain?? (example using a small car towing a big caravan)===put the engine under strain and the temp rises? boost the power of the same engine and the temp moves back to the same temp as normal... (now the fireworks fly) Quote: From: steves-place what is the differance between 16% and 25% nitro fuel?? apart from the 25% being more combustable which has the better lubricating quality?? : Quote Well actually from that info we cant tell you which has the better lubricating quality. What is the oll content of each fuel? Thats what we need to know. If the 25% nitro is 18% oil and the 16% nitro is 12% oil the 25% nitro with 18% oil will lube better. Also going to a higher nitro % (to a point)will actually give you cooler running temps. > Quote: > From: steves-place [quoted text clipped - 9 lines] > Also going to a higher nitro % (to a point)will actually give you cooler > running temps. thanks quakenshack (do they still make those crisps??) been asking this in a few groups and lernt a lot more than i did its sorted now thank all of you for your help .. :) One thing for sure. more nitro = more weight. Nitro weighs more tha even water -- freddy warbir > One thing for sure. more nitro = more weight. Nitro weighs more than > even water. so you dont recomend me using a 5gall tank on a nitro car then ;-) |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.