Heat at Air Intake

[JohnD]

Thanks, Phoenix, I was aware, and mentioned, that the total heat injected into the inlet tract would be the same, but your seminar has better informed me. The OP seemed unsure about which advantage was to be gained, and my suggestion was that hotter fuel would vapourise better, without the added weight and complexity of a refrigeration system. If the object is to reduce the emission of unburnt hydocarbons, would hotter fuel make that better?
John

[phoenix]

Originally Posted by JohnD

Thanks, Phoenix, I was aware, and mentioned, that the total heat injected into the inlet tract would be the same, but your seminar has better informed me. The OP seemed unsure about which advantage was to be gained, and my suggestion was that hotter fuel would vapourise better, without the added weight and complexity of a refrigeration system. If the object is to reduce the emission of unburnt hydocarbons, would hotter fuel make that better?
John

I believe fuel actually burns in a better, more controlled way as droplets - i.e. atomised, not vapourised, so the heat would work against that too. In F1 they cool the fuel and there are rules about how cool the fuel can be relative to ambient temperatures. I remember there being some fuss about fuel temperatures in some cars after the race in Brazil in 2007.

[GORDON STREETER]

Originally Posted by phoenix

I remember there being some fuss about fuel temperatures in some cars after the race in Brazil in 2007.

I thought that was because they can get more fuel in the tank ?

[phoenix]

Originally Posted by GORDON STREETER

I thought that was because they can get more fuel in the tank ?

No, I don't believe so, as fuel tank size is not really a limiting factor because most teams (if not all) can run a one-stop strategy at most circuits if they choose to, but mostly they prefer 2 or 3 stops to suit their race strategy - the computation of which is very complex, involving choices about Q3 qualifying, tyres in the race (as they have to run the option and the prime during the race - only one of which usually gives the best lap time, so two sessions on the better tyre and one on the poorer tyre will usually give an advantage), time lost in the pit lane per stop, where they will emerge back into the 'traffic' etc. etc.

Cooling the fuel does increase the density of course, but that also increases the weight per litre. As air/fuel ratios are based on weight rather than volume of fuel and air, there will be no real advantage from that in terms of power to weight during the course of a race or 'stint'.

Even if the extra fuel load available from cooling gives you an extra lap, you will be carrying that extra dense fuel, and therefore weight, throughout the duration of the stint. So the main advantage must be charge density - giving the possibility of running a higher CR without running into detonation, which will give a power advantage, however modest.

As I know you know, the limitation on engine power is not getting sufficient weight of fuel into the cylinder - that's the easy bit - but getting in the maximum weight of oxygen into the cylinder to burn the fuel is more tricky. To achieve an advantage, higher charge density and/or volumetric efficiency are the only areas available for improvement.


Volumetric efficiency is primarily dictated by cylinder bore, stroke, valve area, engine speed, port design and inlet/exhaust tuning (have I left anything out?). In F1, bore, and therefore valve size, is probably identical in all current F1 engines, as the maximum bore size is set in the regs and using anything less than the maximum bore allowed would restrict valve area. If they all have effectively the same bore they will all have the same stroke to reach the same capacity.

(I reckon, as the maximum bore allowed is 98mm, the stroke will be about 39.77mm - giving a swept volume of 2399.87cc - maximum inlet valve size will be 42.0 - 42.1mm, giving a valve area of between 2771mm^2 and 2784mm^2)

There may be some different tricks played in the port designs by the engine designers, but with CFM I bet they are all very similar too. From experience, I am pretty sure different engine manufactures have taken different approaches to exhaust tuning as, for example, as at the last Grand Prix I attended (Spa) the exhaust note of the BMW sounded very, very different to the Mercedes, the Mercedes to the Renault and the Renault to the Ferrari etc etc. And as we know they are all peaking at the same rpm, the different 'sound' of essentially identical V8s can only be down to the design of the exhausts (although I suspect this affects the shape of the torque curves more than the ultimate power outputs).

So, my key point is, I believe the decision to cool the fuel is motivated by the imperitive to improve charge density for more power, not so more fuel can be made to fit in the tank.

Anyway - time I sat down with my better half! So bye for now.

[Adam43]

Wasn't it so more fuel could be pumped in to the tank? The flow rate is controlled, but if the fuel is denser than you can get more in the tank for the same refuelling time. The advantage, not in the weight, but the length of time you can spend on track.

[AU N EGL]

Originally Posted by AdamAshmore

Wasn't it so more fuel could be pumped in to the tank? The flow rate is controlled, but if the fuel is denser than you can get more in the tank for the same refuelling time. The advantage, not in the weight, but the length of time you can spend on track.

YES and Cold fuel mixed with cold air give better combustion.

That may the reason most tech rules do not allow this.

[Adam43]

Yes, more power on cold days and all that.
I remember reading that it was likely the cold fuel would stay cold for very long in an F1 car. Although even a short lived advantage is still an advantage, but the primary driver was the flow rate from the refueller. Whatever it is better to have it cooler.

[phoenix]

Originally Posted by AdamAshmore

Yes, more power on cold days and all that.
I remember reading that it was likely the cold fuel would stay cold for very long in an F1 car. Although even a short lived advantage is still an advantage, but the primary driver was the flow rate from the refueller. Whatever it is better to have it cooler.

Reducing the temperature of petrol from 30 degrees C to 20 degrees C increases the density by just under 3.3% - so an 8 second fuel stop could be reduced to about 7.44 seconds for the same weight of fuel. So that may well be partly of the answer. I guess you would a range increase of 3.3%, also in terms of Km/litre with the more dense fuel, if you kept filling for the full eight seconds - maybe another lap fuel.

I will have to investigate and report back on what that 10 degrees of fuel cooling will have on the intake charge in terms of density and therfore power output potential - you will be the first to know!

[phoenix]

Originally Posted by phoenix

Reducing the temperature of petrol from 30 degrees C to 20 degrees C increases the density by just under 3.3% - so an 8 second fuel stop could be reduced to about 7.44 seconds for the same weight of fuel. So that may well be partly of the answer. I guess you would a range increase of 3.3%, also in terms of Km/litre with the more dense fuel, if you kept filling for the full eight seconds - maybe another lap fuel.

I will have to investigate and report back on what that 10 degrees of fuel cooling will have on the intake charge in terms of density and therfore power output potential - you will be the first to know!

Got the numbers above horribly wrong last night - so please ignore them.

In 8 seconds the fuel rigs will flow 96.8 litres. By cooling the fuel by 30 degrees from 30 celcius to 0 celcius, the fuel volume will contract by about 0.1% to 96.7 litres - a difference of 100cc of fuel, so the benefit of cooling the fuel is unlikely to be to get more in the tank.

[tristancliffe]

It's the effect of charge cooling from the latent heat of evaporation that gives an advantage - not much of one, but an advantage nevertheless. With the charge cooled by the fuel being at a lower temperature, the cylinder can run closer to optimum lambda and advance, giving slightly more power before detonation or pre-ignition occurs.

[phoenix]

Originally Posted by tristancliffe

It's the effect of charge cooling from the latent heat of evaporation that gives an advantage - not much of one, but an advantage nevertheless. With the charge cooled by the fuel being at a lower temperature, the cylinder can run closer to optimum lambda and advance, giving slightly more power before detonation or pre-ignition occurs.

I agree - this is what I said in post 29.

[AU N EGL]

The two times I have noticed a real difference when the temp was over 95*F track temp was 130* something and the humidity was up in the 80%s

Stepped on the throttle and the car just did not seem to accelerate at all.

and the other time the air temp was 52*F track temp was 60*f Engine felt very very strong, but the track had NO GRIP.

[tristancliffe]

Originally Posted by phoenix

I agree - this is what I said in post 29.

But I said it in less words

[Adam43]

Originally Posted by phoenix

Got the numbers above horribly wrong last night - so please ignore them.

In 8 seconds the fuel rigs will flow 96.8 litres. By cooling the fuel by 30 degrees from 30 celcius to 0 celcius, the fuel volume will contract by about 0.1% to 96.7 litres - a difference of 100cc of fuel, so the benefit of cooling the fuel is unlikely to be to get more in the tank.

That doesn't seem enough. That is an expansion coefficient of 0.0003% per deg C.
http://hypertextbook.com/physics/thermal/expansion/ claims that the expansion coefficient is 950x10^-6 per degree (or 0.095% per degree), agreeing with you first working.
I could believe that they would do it for this reason, although maybe the coolness of the fuel is the driver.

[phoenix]

Originally Posted by AdamAshmore

That doesn't seem enough. That is an expansion coefficient of 0.0003% per deg C.
http://hypertextbook.com/physics/thermal/expansion/ claims that the expansion coefficient is 950x10^-6 per degree (or 0.095% per degree), agreeing with you first working.
I could believe that they would do it for this reason, although maybe the coolness of the fuel is the driver.

Well I may have got the maths wrong again but these are my workings - if I have messed up - please tell me!

950 x 1 litre x 1 degree x 10^-6 = 0.00095

so for 30 degrees of cooling:

0.00095 x 303.15 (degrees Kelvin or 30 degrees C) / 273.15 (degrees Kelvin or0 degrees C) = 0.00105.

Cooling by 30 degrees for 1 litre multiplied by the 98.6 litres flow-limited by the fuelling rig:

0.00105 * 98.6 litres = 0.1020599 (litres decrease in volume)

So, it would be possible, if the re-fuelling rig remained attached for the full 8 seconds, to flow an extra 0.1020599 litres, or 102cc, of fuel.

[Adam43]

A change in 1 deg C is a change of 1 deg K. You don't need the T conversion, all we care about is the change in k, ie 30 deg C or K.

[phoenix]

Originally Posted by AdamAshmore

A change in 1 deg C is a change of 1 deg K. You don't need the T conversion, all we care about is the change in k, ie 30 deg C or K.

Ah - I thought the T conversion is used in the density change calculations - so that is where I thought I went wrong on Sunday. You learn something new every day!

So we have:

0.00095 x 30 = 0.0285

which is a 2.85% change in volume.

2.85% * 98.6 = is 2.8101 litres - so that is the extra amount of fuel that could be filled in an 8 second re-fuelling time with fuel chilled 30 degrees. Just under 2Kgs of fuel.

[JamesH]

So, given the above, is it worth putting fuel through a cooler (as simple as a finned CPU cooler for example? They are very efficient and some have pipework already) which sticks out in to the airstream or has a cool air input from outside ?

[tristancliffe]

Originally Posted by JamesH

So, given the above, is it worth putting fuel through a cooler (as simple as a finned CPU cooler for example? They are very efficient and some have pipework already) which sticks out in to the airstream or has a cool air input from outside ?

Are you planning on refuelling in a race? And are you using flow rates, quantity accuracy and pitstop times where an extra tiny bit of fuel will give any benefit? Once the fuel is in the tank it will very quickly return to ambient conditions unless you bother to cool it there (and even then the power benefits are likely to be measured in Watts rather than KiloWatts.

[neiltb]

a cpu cooler, no. a heat exchanger maybe.

Unless you are flowing fuel at an incredibly low rate the cpu cooler has no chance. A plate heat exchanger with refrigerant would work but is a little obvious!

[JamesH]

The point wasn't anything to do with tank size, it was cooling the fuel just before it gets to the engine to increase its energy density.

The reasons CPU cooler was mentioned was that you can get heat exchanger ones (and they dissipate a LOT of heat with modern processors). If the heatsink was in the airflow (and I am assuming lets say 25cm of pipe is attached to the heatsink/exchanger to get enough volume cooled), then that is quite a bit of cooling.

The question was not to do with the method, but really with the effect. Is it worth cooling fuel just before injection to the engine, to increase performance?

[tristancliffe]

And unless you have a lot of power already the difference will probably be measured in Watts rather than KiloWatts. In short - it's unlikely the additional power will overcome the additional weight of the cooling system.

[dtype38]

Perhaps on cars needing ballast to get up to a minimum weight limit the extra weight of the cooling system wouldn't be so much of a problem. If you could offset the whole weight of the system by reducing ballast then the only penalty would be the weight distribution. IIRC there was a cooling system on the market designed for use on formula cars with intake air restrictors. I can't remember if it was a vortex cooler or a direct expansion nitrogen system, but the idea was that if you're limited by an orifice plate, then pre-cooling the intake air down the veturi towards the restrictor plate would increase the massflow through the plate and hence power potential from the engine. I would have thought a vortex cooler running from a small engine powered air compressor would also be well worth evaluating for gains against power draw to run the system.

[phoenix]

Originally Posted by JamesH

The point wasn't anything to do with tank size, it was cooling the fuel just before it gets to the engine to increase its energy density.

If the volume of the fuel shrinks by nearly 3%, as in the 30 degree cooling example, then the energy density of the fuel will increase by 3%. However, you would only need to inject 97% of the hotter fuel volume to maintain the same A/F ratio.

The interesting bit - which I have been unable to find a solution to - is by how much the density of the air/fuel mixture will be increased by injecting 1 part cold fuel at 0 degrees to (say) 14.7 parts of warm air at 30 degrees. Any thermo-dynamicists here?

[Chris Y]

That reminds me of a vaguely-related question that I've been meaning to ask for some time...

What's easier to change the temperature of - a gas like air, or a liquid like petrol? i.e. for the same volume.

I'm guessing the gas would be, due to lower density? Or am I barking up the wrong tree?