Fuel Temperature 2

[Islander]

Fuel injected 5.9Liter..50 psi fuel pressure.

Fuel rail temp= approximinately 150 degrees.

Installed dual exhaust.
Found stainless fuel line is now 2" from catalactic convertor..
Mechanic says it is fine..shows me a device another car uses to heat it's fuel..said increases mileage.

For performance...would i not want cooler denser fuel?
or would heating it make for better atomization?

Kinda concerned about fuel line too close to exhaust pipe.

 

[wildbill805]

No you do not what to preheat your fuel that will start pre ignition and reduce Horse Power. Cooling the fuel as much as possible is the best thing you can do.

 

[Islander]

I agree but i asked elsewhere ands got..


Be that as it may, when I was at Ga Tech, they had heaters on their fuel rails and they said it made more power. This was a future truck project out of a suburban. 5.3L with an AC induction motor spliced into the drivetrain. We beat all others in the towing and acceleration tests. Goes against all common knowledge, but they said the picked up power by heating the fuel. Their argument was that the warmer the fuel the better it atomized in the combustion chamber.

and

One of the major variables affecting gasoline octane, is reactor temperature. As a rule an increase of 10 deg. F in reactor temperature generally increases the Research Octane of FCC gasoline 0.6 RONC. While Motor Octane is not as dramatically affected by reactor temperature directionally some improvement in Motor Octane should occur when increasing reactor temperature. Motor Octane is affected more by hydrocarbon types. At higher reactor temperature, paraffins crack leaving a higher olefin and aromatic content gasoline. The increased olefins are the major improvers to Research Octane and although olefins generally lower the Motor Octane, there is some slight improvement from the increased aromatic content.

 

[Andy330hp]

Look at Smokey Yunick's work on the "hot engine".

The cool fuel theory is based around the fuel charge actually cooling the air, but that is offset by the poor mixture quality. Islander's statement is somewhat ambiguous. Just how cool? Obviously near-frozen fuel would not be the best thing, so the simple statement "cooler is better" is not true.

Here comes some hard-core guesstimation:

I think it's a balance between a few issues. Obviously you do not want to boil the fuel, but at 50 psi that would be hard to do and not really an issue. Theoretically it should be just warm enough that it fully vaporizes upon injection (ie a temperature slightly above that of equilibrium vaporization at the pressure of your manifold so that it has internally the extra energy required to meet the Heat of Vaporization requirement), but not so hot that it begins to heat the air around it after it vaporizes. Is that really the sweet spot in the real world? I don't know!!

I have long wondered about this very point but have not been able to test it. I know that somebody on this site must have though.

The factory car your mechanic pointed at probably only heated the fuel during cold starts, where the worst emissions are. I highly doubt it was continuously heating the fuel.

 

[GregLocock]

Bear in mind that for certification type on-road use full power is not very important, so a guy chasing good emissions and fuel consumption figures can accept a hit on VE, by using hot fuel. He may even gain in two ways - not only will his heat of reaction be improved, but his throttling losses could be reduced.



Cheers

Greg Locock

 

[ShaunT]

THe heat of vaporization is a key element in choosing what racing fuel to use. I am sure you are talking about street gas here, but I am trying to make a point. The 90% and final boiling point of a fuel is something to seriously consider. The lower boiling point, the faster the burn rate is, but the more prone it is to vapor lock. In the winter, street gas is reformulated with a lower boiling point.
Race gas with a high boiling point of say 250-290 is a slower burning fuel and good for N20 or Turbo's.

Another big factor is that you want an oxygenated gas. Street gas is around 2.5%. MTBE, and Propylene Oxide are oxygenators.

Alchohol has a very low boiling point and hence it's cooling affect on the intake charge. Higher end boiling points are stubborn in regards to that last bit of the fuel wanting to burn.

There is much more to choosing a race gas than just it's Octane index.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[wildcatgeorge]

The most effective burn would be with fuel that is
in a vapor form, liquids do not burn as well, they
need to be atomized with O2 to support efficient
combustion, so to a point, hot fuel would seem to
give better economy, less fuel to get the 14:1
optimum ratio.

If the fuel is not needed to cool the intake charge,
a liquid to gas generator, that could inject the proper
ratio should do wonders to your mileage. This would
be the modern day twist to the Vapor Carb of the 80s.

Darrin

 

[Islander]

actually..I'm interested in increasing performance.

If i thought cooling my fuel to say...45-50 degrees F would increase hp and tq I would do it.

 

[wildcatgeorge]

Propane, high octane and cold fuel, as well as
a cooling effect on the intake charge.

 

[kingaqua22]

We have tested the cooling effect of fuel on our racing car. It is a 2.0l Mazda motor. We extended the fuel line with a copper tube which we spiraled about 8 times, at 30cm in diameter, then dumped then spiral in a bucket with ice water. We did a dyno run before the spiral test and after and found it did not make any difference, even though it dropped the temparature of the fuel by 12deg celcius. Maby it needs to drop more, but we did'nt think it was worth the effort to build something better to test this.

 

[Islander]

so reducing my entering fuel temperature from
150 degreesF to 50 degress F would have little or no effect?

I would have thought as air temperature/humidity determines density of the air charge...that temperature of the fuel charge would affect same(density), thus creating a stronger explosion in the chamber.

Tks for posting about the dyno test.

 

[wildbill805]

I have done some DOE's on just this point. I was monetoring the fuel pressure and fuel temperature of a product supercharged engine at our local drag strip. The results of the DOE showed allot more then temperature and pressure where a factor in the performance of the engine. But a fuel pressure of 65 psi and a fuel temperature of 90c gave me the best performance on a day where the ambient temperature was 65 degrees F but as the temperature of the fuel increased the performance dropped off. Now there were other things affecting the performance but the DOE model did show this to be a signifgant factor and to optimize the performance the model pointed to decreasing the fuel temperature under high boost levels to be the best for performance.

 

[Andy330hp]

In my previous post I meant wildbill805's comment, not Islander's

There will still be a point of diminishing returns. If the fuel gets too cold, then the increase in VE via charge cooling will be offset by the puddling fuel. I think the only time you'd see an appreciable difference is if the car is super/turbocharged. But, I'd also be curious to see the results of cooling your fuel by 100F, than should make SOME difference good or bad.

 

[Islander]

i did cool the fuel some..
..wrapped my fuel rails in radiant heat barrier.
estimate 30 degrees cooler..hard to measure accurately.
maybe it is a placebo effect but seems "perkier"
in heavy stop and go traffic 89F degree weather.

 

[CDC]

From my point of view these trials can create the wrong impression if there are no other changes made to the system.
It is a bit like the story with the special spark plug cables being superior to OEM cables, ignition coils with more power, sparkplugs with more or less gap, different materials etc. All this sort of tests may show a loss or a gain in power WITHOUT making any other changes, and that should be mentioned. An engine on the verge of detonation may well trigger the retard because combustion has speeded up and an engine with too little advance may just give better output because of the same reason. Cooler fuel may well cause a slower combustion, at least initial combustion. Thus to see if you would gain anything you would first have to test an engine on the dyno looking for the best output possible with mixture and timing changes, this would be the base value. Doing the test with colder or warmer fuel you would have to search for the best combination again and THEN see if you had gained or lost.

 

[motorsportsdesign]

I doubt that vaporized fuel will make the most power as the fuel will displace air and reduce the ammount of air being pumped, therefore requireing less fuel resulting in less power.

Jonathan T. Schmidt

http://www.motorsportsdesign.com

 

[patprimmer]

Spot on.
If the fuel stays mainly liquid untill the compression stroke, you get higher VE than if it is vapour in the manifold. This is one reason why LPG engines like big manifolds and ports to recoup some of their lost power

Regards
pat

 

[Louie928]

The original question was in regard to the fuel picking up extra heat from the line passing in close proximity to the exhaust system. Usually fuel that isn't used by the engine is routed back to the fuel tank. After a lengthy drive, the fuel in the tank can get excessively warmed by the continual circulation of fuel through the hot engine bay, and some of it could vaporize. Adding more heat to the fuel probably won't have much effect on short drives, but would cause more heat buildup in the fuel left in the tank. To help keep more constant fuel temperature, I'd suggest a heat shield to protect both the line and the fuel within from the heat.

My '87 Porsche 928 has a heat exchanger as part of the A/C system to cool the fuel that is returned to the tank. This is functuional only when the A/C system is in use to cool the cabin.

Louie

 

[RobWard]

Well, there has been a bit of a debate in Formula One after some teams were found to be pumping the fuel out of their cars in Parc Ferme and chilling it before putting it back. The main problem is that they aren't supposed to do any work on the cars in Parc Ferme and it'd be easy to cheat and add extra fuel. But, they probably wouldn't bother chilling it is they didn't get some results...

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[Andy330hp]

There was post on that on the formula cars chilling fuel in another thread, and I thought the outcome was that it had more to do with cramming more fuel into the tank than increasing power/economy/whatever. I don't remember the thread name, and I'm a little too lazy to look.

CDC has an excellent point. An engine is a system. It is very possible that many of those who are dismissing heated fuel did not try retarding timing a couple degrees, and may have been missing a few hp because of it.

At the same time, don't discount experience. If a lot of people out there (I don't care if they have MS in M.E. or "ASE certified" behind their name) who have been doing this for longer than I have been alive and are saying that cool fuel makes more HP, I respect that, and would treat that as the most accurate hypothesis and move from there.