Modern [with ethanol] mogas vs. 100LL

[digidocs]

I stumbled across some interesting data today:

According to the EPA[1], the average gasoline sold in Houston in 2006 contained 10.07% ethanol and had a Reid vapor pressure (RVP) of 6.92psi.

According to the EAA[2], the specs for 100LL call for a RVP of 5.5-7.0 psi.

This data suggests that mogas with 10% ethanol (in Houston) actually conforms to the 100LL specification for vapor pressure and thus would be no more likely to exhibit vapor lock than "certified" fuel.

Of course, this doesn't address material compatibility, octane, or water issues but its certainly an interesting data point.

Fly safe (and with engineering data),
-DC

References:
1. http://www.epa.gov/otaq/regs/fuels/r...rf/hous-tx.htm
2. http://www.eaa.org/autofuel/avgas/avgas_specs.asp

[Dave Cole]

If the average gasoline sold in Houston had a Reid vapor pressure (RVP) of 6.92psi, that would mean that some gas had a higher RVP, and some lower.

The specs for 100LL call for a RVP of 5.5-7.0 psi, which means that none can be higher than 7.0psi.

Contrary to your conclusion, this data tells me that motorgas with 10% ethenaol does not conform to the 100LL specification for vapor pressure.

[digidocs]

Dave,

You're right. Without data about the variance of those vapor pressure measurements, the strongest conclusion I can make is that on average the mogas in Houston meets the 100LL vapor pressure standards. Thanks for pointing out that misstep.

Doing a little bit more digging, I find that Houston is one of the large parts of Texas that is now subject to the CARB (California Air Resources Board) reformulated gasoline (RFG) phase II requirements that specify a maximum summer vapor pressure of 48 KPa (6.96psi) [1].

So with a little more research, I come back to the conclusion that on-spec gasoline sold in Houston during the summer conforms to the 100LL vapor pressure specification. [This may also be true for the winter but I cannot find any definitive data one way or the other.]

-DC

References:
1. http://www.astm.org/COMMIT/D02_RFGRR0408.pdf

[the_other_dougreeves]

As I posted elsewhere, EPA is revising the ambient standard for lead. The standard will likely come down by a factor of 10x. EPA's proposal is fairly broad, and it's not clear where they set the standard. Many areas will likely not meet the new standard.

In 1980, total US lead air emissions were about 75,000 ton/yr, with about 64,000 ton/yr from leaded auto gas.

In 2002 (the last good, well QAed inventory year available), total lUS ead air emissions were down to 1,700 ton./yr. 100LL was responsible for about 491 ton/yr, or about 29% of total US lead emissions.

As larger point sources of lead (e.g., lead smelters, steel and other metal foundries) continue to get more and more scrutiny, 100LL will become a larger and larger percentage of the total pie.

However, as we all know, we can't just switch from 100LL to 91 octane MoGas. It will take time. Remember that it took almost 18 years to switch cars over from leaded gas.

As I put it in a presentation: "100LL: Doomed, Yet Essential"

TODR