isays

first off, i know this is a kind of bat-**** crazy idea, and you'd have to design an engine specifically to do this... but as a thought experiment:

you could combine your fuel system and coolant systems. Use gasoline to cool your engine. I though of the idea after reading about the Lockheed SR-71 Blackbird (the crazy fast airplane) which uses fuel to cool the insanely hot temperatures when you get above mach 3.

fuel injection engines sometimes recirculate fuel when flow is low to prevent vapour lock (not sure how common it is to do that), why not circulate it around the engine to remove heat? this way you can remove the weight of the coolant. plus the fuel tank can act as a heatsink.

never have to worry about topping off your coolant, as long as you have fuel you have coolant (although the heatsink would get smaller as you drove).

what are the performance implications of injecting hot fuel into the engine rather than cold fuel? fuel injected engines do it anyways, but does it make a positive or negative impact? or none at all?


what problems would this present and how could they be overcome?

the first i thought of would be that the fuel would boil... but since fuel recirculation with fuel injected engines push fuel (rather than pull it), even if the fuel boils it will still circulate. secondly, idle temps of the RX8 on a hot day are above boiling point of water and within normal coolant temperatures... is boiling coolant not a problem?

the most obvious problem would be the danger: if you run very hot (near or above boiling) fuel around your car and you get into an accident, when that fuel spills it will evaporate very quickly and there is a much greater fire danger. what could be done to keep the coolant temperature lower even at idle, or somehow mitigate the fire hazard?

gasoline has a worse specific heat than water does (it isn't as good at cooling things down) so the coolant would get hotter. could this be mitigated by simply flowing flowing a higher volume of coolant and having a large heatsink (gas tank)?

dannobre

iTrader: (3)

So much you haven't though about grasshopper You, think we have fuel bapor problems now

Arca_ex

iTrader: (10)

The reason the SR-71 can use its fuel as coolant is because jet fuel is EXTREMELY hard to light on fire unless it is atomized and under extreme pressure. You could have a decent size puddle of jet fuel on the ground and drop a couple high intensity flares on it and it still wouldn't light on fire for awhile. Gasoline is much more unstable and has a much lower flash point.




Also I hope this is a joke and I'm just getting trolled.

laythor

since gasoline will autoignite at 536 degrees, i'm not sure you will ever see it used as a coolant.

StealthTL

iTrader: (1)

Big problem is the vapor pressure - gasoline contains up to 10% butane in the winter, and at 100*C plus, your gas tank would get big and round, and don't take the gas cap off.....

If the fuel boiled in the engine, the vapor would not cool at all and cause hotspots, melting the aluminum.

The heatsink principle has a fatal flaw - when it's full, it's full and you get no more cooling.

A modern fan-assisted alloy radiator with pressurized custom designed coolant can barely keep up - a heat sink has zero chance.

Highway8

iTrader: (11)

That is some Out of the Box Thinking. I will give you that.

isays

ahhhahaha some of you guys kinda missed the point here:
i know it isn't practical and probably couldn't be made safe for the road...

the point of this is a thought experiment... i know there are problems, but lets identify those problems, figure out why they are problems and try to come up with possible solutions to them.

when you have your engine in pieces, you don't state the obvious "this engine wont work!"... you go about trying to figure out how to put it together again.

i know that the blackbird used fuel with a crazy high ignition / boiling temperature, i know that a heatsink-only solution wouldnt work, i know that there are vapour problems in the fuel lines (in fact, i had already pointed out all these problems in my original post)... lets try to find solutions for these problems. fuel additives, different fuel delivery methods.
rather than using radiators, run a network of tubes full of fuel/coolant under the skin of the car and use the whole body of the car as one giant radiator. stuff like that.

why? because it'll be interesting. its fun because it is a hard problem to solve.

RX8Soldier

iTrader: (24)

That's what I was gonna say lol

I do like this "outside the box" thinking, though!
Solutions to this will eventually come, after all the issues have been laid out before us

Oh, and this is way outside my realm of knowledge! I'm just interested in the conversation

Highway8

iTrader: (11)

I said I liked your out of the box thinking, however I dont see enough benefit to this type of system to make it worth anyones time to try and find solutions to make it work.

Seriourly, what are the benefit it there to use fuel for your cooling system?
Would it increase engine performance/effeciency, or cooling performance/effeciency? If yes to both or either, do the benefits out way all the risk and modifications required to make such a system functional and safe. Gasoline is already flamable, heat it to 200 degrees and have it running through a pressurized radiator that must be positioned in such a location that it is exposed to air and impact danger, well that is not going to be very safe.

BTW, the benefit of never having to top off your cooling system is no benefit at all. Normaly you run out of fuel and your car stops, with such a system, yo would run low on fuel and your car would overheat and then stop.

Now, switch to diesel and there is potential.

StealthTL

iTrader: (1)

Why not use the air in the tires to cool?

Why not use the old motor oil as lipstick?

.....if there are zero benefits, why waste your (obviously eclectic) brainpower on it?

How about developing a better coolant, that would cool without corrosion, never lay down minerals, cool quicker with less horsepower drag, lube the water pump and seals, be cheaper and more environmentally friendly?
Why is it still water based after all this time?

S

Highway8

iTrader: (11)

Evens NPG isnt water based, in certain applications it allows for higher engine temps/engine compression which increases engine and cooling system effeciency. It is essentialy non-toxic. However in rotarys, Evens npg does not allow for increased cooling system or engine effeciency due to the number of heat sensitive components.

dannobre

iTrader: (3)

It doesn't

I find it works better than ethylene glycol/water mixes.....bit of a PIA sometimes but overall I think it has fewer shortcomings

Highway8

iTrader: (11)

I run NPG-R and idont think it cools any better, but I use it for the increased boiling temp. I dont run my car hotter (I dont think it is good for the Renesis), but if I am in the middle of a great lap and I dont want to slow down, I can keep pushing it and there wont be any localized boiling or immediate engine damage.

StealthTL

iTrader: (1)

Evans NPG.

Way to think 'outside the box' but still 'right up against the next box on the shelf'!

I was thinking of a gallium alloy.......

dannobre

iTrader: (3)

I use NPG R as well an I think it does cool better. Might just be the whole system change though....i think the cool down time is shorter tham with EG

isays

if there was no point, then the lockheed blackbird would have just used a discrete cooling system with a special coolant and then used normal jet fuel. there are obviously advantages. we identify those advantages as they apply to automobiles.

some potential (although minor) benefits are reducing the number of pumps you need. if there is a coolant failure there is also a fuel failure so you physically can't run your car without coolant. as long as you can drive you have coolant. never have to worry about topping it off. use of a heatsink means that the engine temperatures stay more consistent rather than fluctuating as the coolant heats up quickly... it'd be good with normal coolant too, but it'd be increasing the weight of the car. this'd take advantage of a fluid just sitting there doing nothing.

but mostly because i think it is an interesting problem. im a software developer... if there is overlap between two systems, i try to find a way that they can share a common set of features rather than duplicating the work for each system. here i see there are three systems pumping fluids around the car, I want to see if there is some way we can combine at least two of them. plus one of those systems has a heatsink just waiting to be used (it is already used by the fuel pump, but that doesn't generate much heat).



So onto the question, first lets deal with absorbing heat. we'll deal with dumping it later.
for me to understanding the problem a bit better:
in fuel injection, when the fuel gets near the injectors it is commonly exposed to large amounts of heat. why is it that it either doesn't boil or doesn't matter if it boils? you're using positive pressure to deliver the fluid, so you don't have to worry about losing prime... is that all there is to it?

an rx8 at idle on a hot day is right around boiling point of water. what prevents the water from boiling locally when the engine is hot, if you're not using antifreeze? is the positive pressure in the system enough to increase the boiling point that much?
or does the coolant flow fast enough so that the effects are minimal and the bubble is taken away and condenses?

Highway8

iTrader: (11)

Jets do not use Gasoline and RX8's do not use jet engines. Those 2 facts alone make your idea unrealistic. Change some of the constants before addressing the variables because there is no way you can make using Gasoline as the sole coolant for an internal combustion engine.

Problem with using a fuel source as a heat sink is that your Heat Sink is always getting smaller.

Consolidating systems is great when they are compatible. Using a flamable liquid in a cooling system is not compatible because you would be creating a receipe for a fire ball on wheels.

Could it be done, YES. Would it improve simplecity, manufactoring cost, vehicle performance? NO. Your fuel pump would have to be much much larger, your fuel lines would have to be much much larger, you would have to make everything out of large non metalic high pressure fuel line and shield everything with flame/spark resistant safety material/structures. All that adds cost and weight.

zoom44

right. it about fuel choice. change the fuel we use and it might be possible.

Highway8

iTrader: (11)

If you want to consolidate systems, think electrical. The regenerative braking tehnology on hybrids is on the right track but could be taken further and made into the sole braking system with a small traditional emergency/back up brake. The future of cars is plug in electic cars with small internal combustion engines as generators. Electrical A/C, power steering and heating are all going to be standard features very soon.

RXeligion

God damn it. I just wrote a long explanation and my f-ing computer dumped it I'll start again.

In the SR-71, the fuel is used to cool as coolant to 1. increase the fuel capacity and 2. reduce the weight of the aircraft. It is possible on a car, but the benefits may be lost. There is a lot to consider:

First, you would need a gas tank specifically designed for the task. It would need two things:

1. a cooling system (which could be as simple as aluminum cooling fins)
2. a venting system to deal with the fumes (which could be safely routed to your intake for extra power or to your exhaust before your cat.

Also, the fuel system would have to be a combination of the two systems currently in place. It would have to be set up basically like this:

Sump (tank)
pump
strainer (filter)
cooler (radiator)
then to the heat reduction channels
*
then to the injectors.

The * marks a place where it would be necessary to have a recirculation line which leads to another heat exchanger (cooler) back to the tank. This is necessary, because it would require much more fuel to cool the engine, than it would to run it, and you wouldnt want to dump excessively hot fuel into the the tank.

It still isnt that simple, though:

You would need to have a strong enough fuel pump to maintain enough pressure on the fuel that it could not approach its gasseous state. This requires constant pressure and flow (which makes starting up your car a difficult procedure and involves bleeding off the vapor trapped at the high points) If you dont do this, you risk air-binding your system, causing heat damage, and reducing (or removing) fuel flow. On the upside, pressure of the fuel will also increase the boiling temperature of the fuel, which could negate the dangers, so long as the pressure is high enough (assuming no leaks, of course)

In a car, it seems like the risk outweighs the benefit. The maintenance that goes into an aircraft like the SR-71 is greater than 1-1 (more than one hour of maintenance for every hour in flight. I wouldnt want to drive a car with those kinds of requirements.

Have I missed anything?

dannobre

iTrader: (3)

How about the fact gasoline just is a very poor choice

Dude...it has everything NOT going for it that is necessary as a coolant

You would be better off trying to figure out how to get a car to burn ethylene Glycol for fuel

isays

i know... as i've said like 5 times. but the problem is still interesting.

thats what this thread is for. to find out what changes would need to happen before it could be done in a car.

I know, i've already raised that concern in previous posts twice.

I know, i've already raised that concern in the original post.

I'm also interested in consolidating electrical systems and making use of waste heat from braking and exhaust., but that would be a different thread.

this is all a big excersize in thought. I know nobody is ever going to do this in a car. I wan't to try to come up with possible solutions to all these problems.
if you don't want to participate, then just don't post.


Thanks to RXeligion for actually taking time to consider the problem before just saying that its not practical. why can't you go strait to the injectors from the filter? is injecting hot fuel worse than cold fuel? anyways, first lets worry about collecting heat. then once we have a good way to collect the heat lets worry about getting rid of it. after that lets worry about the heated fuel in the gas tank. solve one set of problems at a time :p

So, to everybody else... as i asked before (because i think that these are important questions:

in fuel injection, when the fuel gets near the injectors it is commonly exposed to large amounts of heat. why is it that it either doesn't boil or doesn't matter if it boils? you're using positive pressure to deliver the fluid, so you don't have to worry about losing prime... is that all there is to it?

an rx8 at idle on a hot day is right around boiling point of water. what prevents the water from boiling locally when the engine is hot, if you're not using antifreeze? is the positive pressure in the system enough to increase the boiling point that much?
or does the coolant flow fast enough so that the effects are minimal and the bubble is taken away and condenses?

dannobre

iTrader: (3)

Hot fuel is less dense that cool fuel...so we want it as cool as possible. Some vehicles actually cool the fuel...so that might answer your question. Making the fuel temp vary a lot would make tuning have even one more variable

Here's a idea that has about as much merit....

Lets discuss the usefulness of Tabasco Sauce as a lubricant for sex

ken-x8

Liquid fuel rocket engines use fuel as a coolant. The nozzle is pretty much made of fuel and oxidizer lines. Without that kind of system nozzles would melt.

Fuel flow in a rocket engine is way more than for an automotive engine. I suspect that heat capacity times gasoline flow rate in a car is way less than the amount of cooling needed. On the SR-71 the fuel is more of a heat sink rather than a continuous cooling system. SR does not sustain high speeds for all that long. Try dividing out the numbers for its published speed and distance records to see just how quickly it uses a fuel load and has to slow down for more.

Ken

dannobre

iTrader: (3)

The rocket fuel engines use a liquid fuel that is burned in a gaseous state as well...with the evaporative phase in the nozzles...this absorbs a lot of heat.....