Fuel temperature affects mpg?

[Supercharged111]

Don't know if this should go in the economy section or not. Just wondering because I've googled and it appears that cold fuel burns less efficiently? I know colder air has more oxygen in it. I haven't been on in awhile, but I didn't see any winter mpg gripes on the first page, so I thought it might be safe to post this. My AFR's are suprisingly close to where they need to be with the POS black box in open loop SD, so I don't attribute the loss to that. MPG is the same as last year when I was bone stock with a stock tune and O2's, so I rule out that as well. I'm entertaining the thought of fitting a thermostatically controlled fuel heater if I can find a cheap enough liquid to liquid heat exchanger to use coolant to heat the fuel up a bit more than ambient if cold fuel is the cause. I found a good bit on diesels and fuel temps, but not too much on gasoline.

[joecar]

Gasoline temperature effects the port pooling/evaporation rates ("fuel dynamics")...

See tables B3401, B3406... (I'm not sure how to use those tables).

[Supercharged111]

Impact factor and evaporation time, Jesus fucking Christ. My POS blackbox can't do it but my 411 probably will after I install it in a warmer climate. I can't believe those parameters exist. I was wondering more for gee whiz if colder fuel causes crap mileage? Does it not atomize as well at a lower temperature and this is the sole reason for crap winter mileage?

[redhardsupra]

Correct, solid fuel doesn't burn, fumes do. If you really wanna see it in action, get your car up to normal operating temp, get the trims nice and stable, and then go get it refilled with some nice cold fuel. Start scanning again, and you will see fuel trims go absolutely nuts until the fuel warms up and then trims will go back to normal.

The really obnoxious thing for tuning is that there is nothing that measures or accounts for the fuel temp. UGH!

[mr.prick]

Correct, solid fuel doesn't burn, fumes do. If you really wanna see it in action, get your car up to normal operating temp, get the trims nice and stable, and then go get it refilled with some nice cold fuel. Start scanning again, and you will see fuel trims go absolutely nuts until the fuel warms up and then trims will go back to normal.

The really obnoxious thing for tuning is that there is nothing that measures or accounts for the fuel temp. UGH!

LTFTS are highly negative for a few miles after I fill up.

[joecar]

When cold, the pool (on the walls of the ports) evaporates slower (since evaporation rate depends on temperature), so, based on ECT, the PCM adds more fuel to increase the size of the pool which speeds up the evaporation (since evaporation rate also depends on surface area)...

(...I don't really understand it yet...)

so I suppose the extra fuel used reduces your MPG figure.

[5.7ute]

When cold, the pool (on the walls of the ports) evaporates slower (since evaporation rate depends on temperature), so, based on ECT, the PCM adds more fuel to increase the size of the pool which speeds up the evaporation (since evaporation rate also depends on surface area)...

(...I don't really understand it yet...)

so I suppose the extra fuel used reduces your MPG figure.

This would only be during transient airflow though. Once the airflow is stabilised the pcm would not need to inject more fuel as the puddle (tau) would be constant.
Also manifold pressure will have an effect on evaporation rates.

[joecar]

This would only be during transient airflow though. Once the airflow is stabilised the pcm would not need to inject more fuel as the puddle (tau) would be constant.
Also manifold pressure will have an effect on evaporation rates.Ah... I am still learning the details...:cheers:

[5.7ute]

It's certainly a complex model, and not easily logged. I tried with the calc ipw pid but the available precision wouldnt let you easily see it.

[gmh308]

Impact factor and evaporation time, Jesus fucking Christ. My POS blackbox can't do it but my 411 probably will after I install it in a warmer climate. I can't believe those parameters exist. I was wondering more for gee whiz if colder fuel causes crap mileage? Does it not atomize as well at a lower temperature and this is the sole reason for crap winter mileage?

Yes cold fuel and cold engine means ECM needs to dump more fuel in to get the AFR into the right space for cranking and cold run as it takes a lot more fuel to get the same degree of vaporisation in the combustion chamber.

For example 2x more fuel at 32F than 70F. Almost 9x more fuel at -40 than 70F, for cranking to get initial fire up.

Run fuel at -40 is 3x run fuel at 70. About 2x at 32F.

Once the fire starts, not so bad. :)

[Supercharged111]

I know ECT's affect mileage, but it wasn't until very recently that I suspected cold fuel being another cause of crap winter mileage. The concensus here seems to confirm that. Has anyone ever screwed with a thermostatically controlled liquid to liquid fuel heater using warm coolant to warm the fuel to a certain ideal temperature?

[hog]

I know ECT's affect mileage, but it wasn't until very recently that I suspected cold fuel being another cause of crap winter mileage. The concensus here seems to confirm that. Has anyone ever screwed with a thermostatically controlled liquid to liquid fuel heater using warm coolant to warm the fuel to a certain ideal temperature?

I remember that Smokey Yunick did some "hot fuel" testing. He got better fuel economy by pre-heating the fuel. I am pretty sure he was using carbs for his testing.

peace
Hog

[gmh308]

You are spot on. Back in the carb days there was a lot of experimentation with getting fuel and air warmer to maintain or improve vaporisation.

Hence the move in later years, when fuel economy and emissions became more important that OEM's moved to coolant then exhaust heating under carbs.

EFI did away with a lot of that with its proximity to the intake valve. Still a challenge in cool conditions on cold start though. Nothing like heat to vaporise fuel. Though it seems to be a tradeoff these days agains excessive HC emissions, as GM at least moved their fuel recirculation to the rear of the car to cut down on excessive fuel heating.

Guess better overall HC emissions reductions are made at the tank than at the engine.