ASTM: Gasoline Today and Tomorrow – An Executive Report

Octane Week | ASTM: Gasoline Today and Tomorrow - An Executive Report
(from p16)
of an offset,” he told ASTM members
meeting in Pittsburgh. “The DI change addresses a
technical issue that arose out of CRC studies. The
secondary aspect, to have it apply at retail, grew out of
state positions in the past.”
The most recent CRC study, completed in 2004,
was “probably the best cold-start driveability program
run,” said Task Group member Lew Gibbs of Chevron.
Vehicles were screened for responsiveness, raters were
trained and calibrated and procedural changes were
made to the program. “The result showed a high degree
of statistical correlation between driveability and an
adjusted DI index.”
In contrast, previous CRC tests included older cars
and a larger ethanol offset, Gibbs explained. “The latest
test had the best representation of modern vehicles
on the road,” he told Octane Week. After meeting in
Naperville, Ill., to discuss the results, Task Group
members determined to propose balloting a DI change
to the entire group.
Specific Proposal Language
The proposal to be balloted was as follows:
Change Table 1, footnote C, to read
“Driveability Index (DI) = 1.5 T10 + 3.0 T50 +
1.0 T90 + 1.33 o C (2.4 o F) * Ethanol Volume%
where T10 = distillation temperature, o C
( o F) at 10% evaporated, T50 = distillation
temperature, o C ( o F) at 50% evaporated, and
T90 = distillation temperature, o C ( o F) at 90%
evaporated.”
Change footnote D with the following:
“During spring and fall transitions into and
out of the federal vapor pressure control
period, the Driveability Index requirement
of the volatility class specified in Table 4 is
waived so long as the DI meets that of the
volatility class corresponding to the measured
vapor pressure of the retail sample.”
Refiners might have to tighten the base fuel
properties in order to accommodate DI with an ethanol
offset. A 2.4ºF *10 vol% translates to a 24-point more
stringent spec.
Task Group members expressed concern about the
impact on conventional gasoline. At that time, refiners
did not know whether ethanol would be added to CG
downstream of the refinery, which would create a noncomplying
blend.
But as Gibbs pointed out, when ethanol is added at
10 vol%, it lowers the 10% and 50% evaporated points,
which in turn, lowers DI about 60 points, on average.
The ethanol adjustment for 10 vol% is only about 24
points. Since the upward adjustment is smaller than the
downward blending effect, the blends will always be in
compliance, he said.
A 24-point more stringent spec will mean
additional manufacturing costs for refiners, one fuels
industry representative said. “This is going to cost more
to produce,” said Bob Schaefer of BP.
The DI change is coming at a time when refineries
are running at maximum, Schaefer pointed out. In the
future, refiners will have to make additional amounts
of low-Rvp fuels due to the implementation of the U.S.
EPAʼs 8-hour ozone standard. That will probably lead
to fuel quality changes. “States will need emissions
reductions, and fuels will be on the list.”
Schaefer observed that the latest CRC study utilized
a fuel set of 10 fuels, eight of which had a DI in excess
of the current ASTM maximum of 1250. “The majority
of the fuel set contains fuels that are non-compliant,”
he noted.
A correlation was developed between the effect
observed on high-DI fuels and applied to the on-spec
fuels.
CRCʼs research was “good science” Schaefer said,
“but the application of the correlation would not be
good science.”
Testing a broad range of fuels is common at CRC.
Two of the test fuels had DIs below the 1250 maximum
and four were around 1265, Chevronʼs Gibbs countered.
Previous tests included fuels with DI as low as 1160,
and they showed an offset for ethanol was needed. “We
expanded the envelope to get a scale so you can see
an effect. Thatʼs common practice and accepted good
science.
“The relationship between the adjusted DI and
driveability demerits was linear on a log basis, indicating
applicability at lower DI levels,” Gibbs said. “Members
of the auto, oil and ethanol industry all agree that this
offset has applicability.” (continued on p18)
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