Fuel Temperature
Fuel Temperature
(OP)
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.
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.





RE: Fuel Temperature
RE: Fuel Temperature
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.
RE: Fuel Temperature
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.
RE: Fuel Temperature
Cheers
Greg Locock
RE: Fuel Temperature
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)
RE: Fuel Temperature
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
RE: Fuel Temperature
If i thought cooling my fuel to say...45-50 degrees F would increase hp and tq I would do it.
RE: Fuel Temperature
a cooling effect on the intake charge.
RE: Fuel Temperature
RE: Fuel Temperature
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.
RE: Fuel Temperature
RE: Fuel Temperature
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.
RE: Fuel Temperature
..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.
RE: Fuel Temperature
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.
RE: Fuel Temperature
Jonathan T. Schmidt
http://www.motorsportsdesign.com
RE: Fuel Temperature
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
RE: Fuel Temperature
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
RE: Fuel Temperature
"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams
RE: Fuel Temperature
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.
RE: Fuel Temperature
I would guess the temperature of the gas is more critical to its distribution to avoid vapor lock and minimize dissolved gases in the gasolne rather than its cumbustion qualities.
Random thoughts of an HVAC engineer
Bill
RE: Fuel Temperature
RE: Fuel Temperature
The SUs are fitted to a pair of "experimental" siamesed inlet manifold castings, cast in aluminium, the engine intake ports being in arranged in two adjacent pairs (port configuration is: Ex,In,In,Ex,Ex,In,In,Ex).
The carb end of each inlet manifold has a round port (1.25 inch diameter), to match the SU, this changes to an oval shape mid section, tending towards a figure of eight profile at the cylinder head, where the adjacent intake ports suck at the whole diameter of the small "plenum" this profile gives, there being no dividing wall inside each manifold. The manifold length is about 4 inches from carb face to inlet port face and is about as close to "straight in" as possible, with very little charge turbulence occurring.
The original setup was a single semi-downdraught 1.25 inch SU, sitting on a water heated plenum casting above a 1 into 4 ally manifold. The tortuous path the intake air followed with this has to be seen to be believed, possibly a major restriction on power output, only beaten by the appalling cast iron exhaust manifold and single downpipe. My engine has a 4 into 1 tubular exhaust manifold of increased diameter, to a straight through muffler.
Since fitting the twin carbs it has suffered from poor fuel economy and produced less power than I expected, bearing in mind other mods on the engine. I have found some difficulty in getting the correct mixture. The carbs spit back at mid to high revs, a symptom of weak mixture, despite trying progressively richer needles. The strange thing is, the tailpipe is very sooty and the exhaust blows black smoke but the colour of the plugs tend to show too weak, which ties in with the spitting back.
I suspect that the little intake manifolds are too short and too cold, not allowing efficient vapourisation of the fuel droplets issuing from the jets. This possibly results in large fuel droplets and inefficient combustion, so much of my precious UK fuel is going down the tailpipe as soot.
I am about to change to a single choke downdraught Weber carb on a modified original manifold (discarding the separate heated plenum). This setup has reportedly given very good results on this type of engine, with up to 25% improvement over the single SU claimed by one very reliable exponent. No-one has so far explained why this should happen, but it is possible that the longer path from carb to inlet port gives better fuel vapourisation than my setup. I think that my setup is great for gas flow but poor for fuel atomisation.
I will report the results.
RE: Fuel Temperature
there is one piece missiong from this idea of cool fuel
gasoline's octane drops over time due to evaporation. more heat equals more evaporation. so all your high octane bits get sucked into the charcoal can and the low octane stuff is what gets left to burn.
so I highly reccommend insulating your fuel line that runs a bit close to the exhaust.
(this is also why you want to make sure your sealed fuel system is truely sealed)