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Fuel warming for fuel economy 2

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Blob97

Blob97

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May 25, 2004
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The radiator that I am currently running is set up to also function as a tranny cooler. Because I have a manual tranny I have no need for this function. Would there be any fuel economy benefit to running the fuel through this core in the radiator?

The vehicle is a 1996 Dodge Neon
198K Miles
 
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No, but it might increase the chance of a fuel leak and fire in an accident.

Regards

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I would be thinking of the following.
The fuel temp can get to about engine temp of between 190 and 210*f. Will the injectors overheat in addition to there normal electrical operating temp elevation?
Will fuel expansion cause regulator problems?
What are the effects of elevated fuel tank temps?
Will the fuel pumps have shorter life under higher temps?
What benifit would there be to elevating fuel temp on combustion efficiency?
As the fuel is heated and sprayed into the air stream, the speed of combustion could be increased as though it were lower octane fuel and may cause ping from (now) to much ignition timing.
Usually in performance application the fuel is cooled to get density increases in the capacity of the air stream to take more fuel and cylinder packing for more power.
There are many inter-related relationships that go on so we go with a normalized world of operation. Intentionally change one thing and other things also change.
 
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I would suggest that you do nothing to increase fuel temps.

You would probably find that your fuel economy will actually decrease. This will be due in part to the light ends of the gasoline evaporating in the rail and finding there way out of the injector nozzle, which will always be dribbling slightly. This evaporation will also cause vapour lock within the rail and hard hot restarting.

Depending on the type of fuel system you would probably notice fuel smells in the cabin. Likewise if your vehicle is fitted with a fuel tank purge system then the carbon canister will more likely be full most of the time, providing smells outside as well.

Point to note: Ping is not caused by rapid combustion, it is caused by autoignition. Rapid combustion will actually reduce detonation as the end gases are consumed before they can autoignite.

MS
 
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The difference between the enthapies of formation
Code: 
n-Octane vapour       C8H18(g)  -208450
n-Octane liquid       C8H18(l)  -249950
kilojoules per kilomole, is about 20%.

However, in a calculation of the heat released by burning it ...
Code: 
CO2     8       Carbon dioxide  -393,520        3148160
H20     9       Water vapour    -241,820        2176380
C8H18  -1       n-Octane vapour -208,450        -208450
                                                5116090
... breaking up the fuel plays only about a 4% role in the energy produced by combustion; the main energy coming from carbon to carbon dioxide and hydrogen to water reactions, and that mainly as a result of multiplicity: the number of times the reaction occurs rather than the energy per reaction.

The end effect, 40 thousand in 5 million - less than 1% - is the most you could hope to gain.

I had a bottle of unlaballed sparkling wine from the cellar at lunch so apoligies if this isn't quite right.
 
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Having done most of the calculation, I guess I could just add that dividing by an atomic weight of 8*12 (carbon) + 18*1 (hydrogen) = 114 gives 44,877,982 megajoules per kilogram for n-octane vapour, based on the above figures.
 
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Hi Blob
I've actually done this before. I noticed 3 things:
1. There was an improvement in fuel economy. Noticeable but not much.
2. The vehicle had better acceleration from a standstill.
3. The engine pinged quite a bit and the timing had to be retarded.
The engine ran well when cruising but would vapor-lock in city traffic and when idling - not very reliable. Also, if one was in an accident and the insurance company inspected the vehicle, they would probably void their coverage - whether the modification was relevant or not. Combine these things with the already mentioned fire hazard and I was paranoid to drive the thing.
However I believe there is something to the idea. I think there is an optimum fuel temperature for each application. One would probably need a computer to monitor and control it. In some climates, the underhood temperature would be over that optimum anyways. It might be worth pursuing, but not by your average mechanic or tinkerer.
 
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Drag and land-speed cars have been cooling their fuel for over 40 years years for more power. Here's a "Cool-Can" from Moroso, that uses regular or dry ice.

MOR-65125.jpg
 
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I guess if you use a litre of hot fuel to get a certain distance, a litre of cold fuel might take you further as it weighs more and therefore contains more energy per litre, but maybe the car will be slower as it will be a gram or two heavier ;-)

If combustion efficiency were a real issue, there might be some point to this, but as most losses are due to heat escaping into the cooling system and out the exhaust, I don't see much potential for gain by focusing on the already quite efficient area.

Regards

eng-tips, by professional engineers for professional engineers
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Cooled fuel makes for better atomization, not more fuel in the lines.

Hot fuel is not good and will also cause the fuel pump to die young. Do you really think Blob is inventing something here?

 
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Thermodynamically there is no doubt in my mind that for ultimate fuel economy (ignoring practicalities) hot fuel would be more efficient. But we can't ignore practicalities, we are engineers, not scientists.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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How will cooled fuel make for better atomization? I think that in a gasoline engine the cooler the fuel, the larger the droplets, the poorer the combustion?!? Infact I think that with cooled fuel there is a real risk of puddling, quench, borewash and tipin stumble/hesitation.

Also, in a PFI engine anything that causes wall hangup to increase can result in part load misfire. This is us calibration engineers spend so much time in cold climates using hot climate fuels (think RFG2/CARB Phase2 in Alaska). The driveabilty of vehicles in these situations is horrendous.

MS
 
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My experiments show that the best atomisation is at it's boiling point. Hardly cold.

The higher the kinetic energy in a molecule, the more they will separate from each other. Kinetic energy in a molecule is directly related to temperature, higher relating to hotter.

When you consider the temperature, mass and specific heat of air vs the mass specific heat and temperature of the fuel consumed by an engine, the temperature of the fuel is insignificant.

The very first thing to leak fluid in a car involved in an accident is the radiator in almost all cases. Putting hot petrol there will in my opinion, substantially increase the risk of fire, for an insignificant improvement in atomisation.

Regards

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Blob97,

In order for fuel to combust it must be in a gaseous state. If you have every conducted a flammability test you will immediately realize this.

The Holy Grail for any Internal Combustion Engine would be to convert all of the fuel to syngas prior to combustion without forming tar, gums, etc.

You cannot do this with a small spark or compression-ignition engine.

Any and all marine engineers are well aware of preheating fuel prior to injection or combustion in boilers, diesels or gas turbine engines.

The purpose is twofold:
(1) Remove water
(2) Prevent wax formation in injectors or nozzles

Preheating fuel has many advantages, but must be done safely.

Reducing droplet size increases surface area, thus more fuel can vaporize in a shorter period of time. It is the gaseous vapor layer that surrounds the fuel droplet that burns away. Not the droplet of fuel.







Todd
 
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The post by Fabrico illustrated a fuel cooling can. Cooling the fuel cools the overall intake system. This helps cool the incoming air. Cooler air is denser air. Denser air has more O2. More O2 allows more fuel to maintain the proper air/fuel ratio (stoichiometric). More air plus more fuel = more horsepower. Another example of this is the intercooler on a turbo-charger. It's only function is to cool the intake charge to allow more air and fuel into a given cylinder. I'm not sure if routing your fuel through a radiator transmission cooler will actually cool the fuel, but the concept of cooler fuel is sound.
 
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oxilume, I am not disputing your post, however, heated gasoline causes vapor lock, among other problems. Atomization is certainly important, but the intake manifold configuration and combustion chamber design have more effect on this than the temp of gasoline. The original question was about fuel economy, and he referenced running the fuel through a cooler. In the real world, cooling the fuel can increase the fuel economy, given proper tuning.
 
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I wasn't going to bring this up because it is entirely different than Blob's idea. It is however related to the topic. This has been around for a long time and has been to high places and back down. If Smokey says it's so, it probably is.


dia1.png
 
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It's a strange picture format, if it does'nt load, hit the "Refresh" button.

BTW, there are numerous mentions of this system on the internet.

 
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