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 Help Gasoline Characteristics, Street/Pump, then and now? 
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Joined: Sun Jun 23, 2013 1:41 pm
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Location: Phila. Penn.
Forgive me, my search skills are failing. I thought Shrinker had posted some characteristics of pump fuels, but I can 't find it. I understand street fuels can and have varied in RVP, distillation curve, etc; but a range or a few specific examples would be helpful in wrapping my head around the situation.

Most interested in motor octane, reid vapor pressure and distillation curve.
More interested in Summer fuels than winter blends with their high RVP, but any info is better than no info!

Tue Aug 26, 2014 6:20 pm
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Tue Aug 26, 2014 7:40 pm

Joined: Sun Jun 23, 2013 1:41 pm
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Location: Phila. Penn.
Thanks Mark. That's better than I came up with. Maybe slightly different key words or who knows. Some of those graphics look like promising links. For the winter/summer RVP, I found the EPA rule and got to read through all that... the EIA page is much more to the point!

Tue Aug 26, 2014 8:49 pm
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Turns out that much of that wasn't about current automotive gasoline. But it did get my search moving in the right direction.
This all started because I had a problem twice this summer with my street vehicle (powered by a fully smogged, carburated, AMC 360). Both times the fuel was premium from the same brand - but different stations. Both times the weather was high humidty, at higher altitude, and the engine had been shut off and restarted about 1/2 hour later.

The other reason for my interest is that my competition vehicle has winter (specificly December) pump fuel in it. That reared its ugly head while testing out the new brakes linings. After about 10 minutes light driving it would cut out and die under just the right moderate load.

Many of the sources I found are from the era when MTBE was either coming into or going out of use, ie related to "reformulated gas." The most authoritative source on the properties was not of commercial street gasoline, but study on the effects of various formulations. It is CRC-E67, Durbin is lead author and can be found here ... 67_rpt.pdf
All the fuels combinations had RVP around 7, so they all represent summer blends. They used fuel specified at 50% and 90% evaporation on the distallation curve, called T50 and T90. Which T50 and T90 may best represent fuel today in a region of the US I do not know. That said, the distillation curves for all the variations they tested fell within a range of:

Distallation evaporation points in degrees Farenheit

I've seen it claimed that today's up-to-E10 pump gas can have a 10% evap around 110 degree. (See IEA-AMF for example)
One of the few retail street fuels with specs is sold in the Alberta region. I suspect it is a rather different blend than most of what us are getting in the lower 48 states. (see UFA)

One of the biggest differences I see between race fuel and even street legal race fuel like GT260 is the 90% distillation is much lower. For comparison.:
260GT 95.0_100_105__0.734__6.4__145__211_216_xxx__3.7__9.8%

I have to believe that one advantage of race fuels for short effective compression strokes is how quickly they finish off the burn. This seems to be what Shrinker was trying to get across. Maybe old time street fuel was like that too???

*edit - If anyone can explain how to make a nice table, I'd be much obliged.

Fri Sep 05, 2014 10:47 am
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Made a graph of the distillation curve of fuel someone on another forum had tested a few years ago.
It shows a couple of things. One, with ethanol in the mix its important to see more than just a few points on the curve. Another is that with eth, the percentage of fuel that can evaporate at under hood temperatures is larger than the 10% and 50% alone numbers would suggest.

Fuel-distillation-2007.png [ 20.14 KiB | Viewed 915 times ]
Sun Oct 23, 2016 11:48 am
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Pump gas is a crap shoot. Sooner or later you will get some that will not ignite or burn at all when the engine is cold and you will spend a lot of wasted time trying to fix ignition that has nothing wrong with it.

Sun Oct 23, 2016 12:55 pm

Joined: Sun Jun 23, 2013 1:41 pm
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Location: Phila. Penn.
I hear ya Tuner. Especially right now when we're switching to winter formulations. But it is helpful to understand the general trends and how they changed- At least for those of us working with fairly stock engines from the 60s into the 70s and 80s.

My first point was to highlight that using only the typical distillation reference points; T10, T50, T90 and T100, could be misleading. So the graph was a corrective to my earlier post. Its interesting to see that fuel with around 10% Eth can lower the evaporation temperature for close to 30% of the fuel! So if it has more than a little Eth assuming a smooth line from T10 to T50 will probably be wrong. We can figure this not only changes the burn, but helps explain what can happen when the carb and fuel lines get heat soaked in a hot engine compartment.

File comment: Same Fuels plotted with smoothly interpolated lines.
Fuel-distillation-interp.png [ 22.98 KiB | Viewed 865 times ]

FWIW, here are a few more pairings of fuels. These are Test Gasolines from the CRC Study. They are similar but not the same as what actually gets sold. This 2006 study was forward looking, trying to determine the impact of various formulations by changing just one major variable. I selected A & B which are nearly the same formulation but B has 5% Eth; K & L which represent reformulation with MTBE but K has 0 Eth and L has 10% Eth.
Fuel-distillation-2007-RFGtestsv2.png [ 31.39 KiB | Viewed 865 times ]

Data for Tier 2 EEE testing fuel without any alcohol is from "Optimal Ethanol Blend Study" Richard Shockey et al. Energy & Environmental Research Council, Nov. 2007. (Note: This research study was done for the American Coalition for Ethanol) RVP 9 - 9.1, RO 96.6, MO 88 (therefore a AKI of 92.3) density of .742

Last edited by Mattax on Sat Oct 29, 2016 8:44 am, edited 3 times in total.

Fri Oct 28, 2016 10:06 am
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Location: Phila. Penn.
For comparison, here are distillation points for a few off-road fuels.
For 100LL Av gas I found a BP (UK) website had a more complete data online than Exxon (USA) .
The Sunoco Race fuels only listed T10, T50, T90. Note that 260GT is an oxygenated, street legal (if so taxed) fuel using Ethanol. Based on what I had learned above, I felt it would be a mistake to attempt to sketch an interpolated line for the Sunoco fuels.

However it does seem fair to conclude that race fuels tend to completely vaporize and burn in a much tighter temperature range than pump gas bought for street use.
Fuel-distillation-Race-AV-2007.png [ 26.99 KiB | Viewed 864 times ]

Fri Oct 28, 2016 10:26 am
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Good info. Thanks for posting Mattax

Mon Nov 07, 2016 12:11 pm

Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Motor Gasolines Technical Review (pdf) 2009 Chevron.
A lot of good info in here about gasoline characteristics and what they effect.
From Chevron Canada website. The link was posted on moparts race forum and it seemed good.
Topics include:
Gasoline and Driving Performance
"do." and Air Quality
Refining and Testing
Oxygenated fuels
Engine Deposits
Handling Safety

Thu May 25, 2017 12:48 pm
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