Guilty

I saw this in a book the other day. It was a can that you put around your fuel lines so that you could put ice in there to cool your fuel. Don't think you could use this on a Tib or anything but does it actually work?

Red

You know, I had been giving some thought to this...

Everything is more dense when cold, because cold basically equals "less excited" atomic structures and so they all settle down and pack in a bit tighter. So cold air is nice, because you can basically pack in MORE air (density speaking) with the same engine, so along with more fuel you will get more power.

But, let's flip this around...

You have cold FUEL, but still have hot air (turbocharged for example) Ok, so the more dense FUEL will be sprayed on top of hot air. Well now you have more fuel than you really needed, so you start running rich(er). This doesn't create more power...

Of course, there are secondary objectives to cold fuel. First off, it can help cool down the combustion chamber surfaces, leading to potentially less detonation if you're running the engine at the bleeding edge of performance. The cold fuel could also cool off the air a small bit, so maybe you'll get some help there...

I guess I could see it adding some help, but I guess it would just depend on how much fuel your car really sucks down. If you're driving a little gas-miser econobox (which, like it or not, all of us Tiburon/Elantra/Accent owners are) then I'm not really sure how much you'd see.

But if you're running bigger displacement OR you're running some forced induction (dynamically bigger displacement) then the added fuel needs may benefit from some cooling.

So, um, yeah it would work. Just not sure on a STOCK car (or just I/H/E setup) you would really get out of it.

My $0.02 for the moment,

Guilty

So if it makes the fuel more dense would you benefit anything from this if you were running NOS? Since NOS is cold as well.

Veniston

Well, this is sort of a thermodynamic argument, so I'll throw my hat into the ring.

The expansion (& contraction) of liquids with temperature is a lot less than gasses. From a quick look I believe that the expansion coefficient of air is .00367/°C, while petroleum seems to be in the range of .0006 to .0009/°C.

Add in the fact that the volume of fuel used is a lot lower than the volume of air, and the density changes will not have a great affect on the richness of the mixture.

The important thing to note during combustion is that the liquid does not burn. What actually happens is that the fuel evaporates into the air, and the A/F chemical mixture[1] ignites. The evaporation will take place naturally until the air is saturated with fuel--and it happens fast because of the heat residing in the cylinder.

Now, when any liquid evaporates, it takes energy from the surroundings. Water in a pot takes heat from the stove to boil, nitrous from an injector gets cold as it is released because it is naturally a gas at atmospheric conditions; it takes heat out of the surrounding equipment as it changes phase. Water(I work with steam most often, I have numbers for it) at room temperature as a liquid has a specific enthalpy of 33 btu/lb (sorry about the archaic units, btu's are a measurement of heat energy), boil it to a vapour and it has 1150 btu/lb. This means it must absorb about 1117 btu/lb during the vapourization process, at the same temperature. If you were going from lower temperature, chilled water to higher temperature steam, like the situation with our fuel, the energy absorbed is even greater.

So as the fuel enters the chamber it should be changing phase from liquid to vapour, and absorbing heat from the surroundings. The cooler the fuel, the more energy it will take out as it changes phase[2]. More heat taken out=lower temperature=more dense mixture. And really, it would scale to your system, sure our cars use less fuel but then again they also use less air. Proportionally, the effect is the same.

Now, I'm not saying that this mod will actually give you any real benefit, just that the principles seem sound.

Notes(simplified somewhat for the general audience):
[1] Chemical Mixture: in this case the fuel is being held in its gaseous form as individual molecules with weak ionic bonds to the air, as opposed to a being a mechanical mixture of 'drops' of liquid fuel floating in the air.
[2] The fuel should change phase quite quickly as it exits the injectors. Clean injectors spray out the fuel as a very fine mist, dirty ones cause larger droplets of fuel to form. Evaporation rate is a function of surface area (among other things), and a fine mist of small drops has a lot more surface area than fewer, larger drops. Larger drops don't fully evaporate, and so don't get consumed (liquid doesn't burn!); resulting in partial combustion and all the crap that leaves you with.

Curtas

I agree completely with Veniston. No appreicable change in fuel density, but it will cool the overall AF mixture, which may help.

Now, it may be only a 0.001 % gain. The main rule (which is straight out of Turbochargers and Maximum Boost books) is until you see race teams using it, caveat emptor (buyer beware)

ac

Random

As Red stated...on a forced induction system, it might be a good idea, but on a N/A car, I don't see how it would have much, if any benefit.

The other problem you can run into is liquid fuel. Believe it or not, you don't want gas in liquid form...you want it in gasious form.

As Venision stated, the fuel evaporates into the intake air stream, cooling it somewhat, and it is that evaporated fuel/air mix that actually ignites.

If you cool the gas down, it will require more heat from the intake air stream to evaporate it, and also more TIME!!!! There only about 2" tops between the injectors and the intake ports. A high RPM that fuel covers that distance fairly quickly, so the cold fuel does not have much time to accurately mix with the intake air and warm up and evaporate.

The fuel then litterally dribbles into the combustion chamber when the intake valves open. Most of the fuel will be evaporated off the cylinder walls by the cylinder wall heat, but it will take that oil layer that your rings seal against with it. It will also not be properly mixed with the intake air.

So in effect, you could be actually delivering LESS "usable" fuel into the combustion chamber and causing increase ring/cylinder wall wear.

This is of course assuming the fuel is actually too cold. I think in reality, an "cool box" would not drop the fuel tempature by more than a few degress, maybe as much as 5 or 10. Thus, not enough to cause the problems I am describing...but, it is one of the "theoretical" drawbacks. Most engines do not have a fuel tempature sensor and do not alter ECU programming for fuel tempature. If they do, the assume the fuel tempature is "ambient" and use the intake Air temp sensor for a reading of "ambient" air. Some serious hard core race engines do measure the tempature of the fuel, and do take that into account in their tuning.