Materials Compatibility
Two general problems are associated with using E85 as a
replacement to standard gasohol (E10). First, materials
that would not normally be affected by gasohol may
degrade in the presence of alcohols. Second, alcohols are
more conductive than gasohol, which promotes galvanic
corrosion by acting as an electrolyte. Materials that
degrade in the presence of ethanol blends with high
alcohol concentrations include brass, zinc, lead, and
aluminum. Corrosion products from material degradation
can damage and plug fuel system components.
Plastics and rubber components degrade in the
presence of ethanol as well. These parts need to be
replaced with an alcohol-resistant elastomer. Viton® is a
flurohydrocarbon elastomer with the highest continuous
heat resistance and outstanding resistance to swelling.
Viton® has high resistance to permeation when in contact
with aggressive alcohol fuels, such as E85.
The corrosion behavior of various commonly used
materials in the presence of pure ethanol is detailed in
Table 1.
Table 1 -Corrosion of materials in the presence of
100% ethanol[4]
Material Compatibility Issue
(Penetration level of)
Aluminum < 2 Mils/year up to 180°F
Brass < 20 Mils/year up to 210°F
Bronze < 20 Mils/year up to 400°F
Carbon Steel < 20 Mils/year up to 230°F
Copper < 20 Mils/year up to 110°F
Nickel < 20 Mils/year up to 200°F
Type 304 S.S. < 20 Mils/year up to 210°F
Type 316 S.S. < 20 Mils/year up to 420°F
Titanium < 2 Mils/year up to 200°F
However, the penetration of materials in contact
with ethanol is only half of the problem. Ethanol is most
corrosive acting as an electrolyte in a galvanic corrosion
environment. A galvanic series table should be consulted
in conjunction with Table 1. For example, aluminum
exhibits low penetration levels up to 180°F. However,
aluminum is anodic to most materials and will corrode in a
galvanic corrosion environment when in contact with a
second dissimilar metal.
Currently, there is no galvanic series table
indicating the activity/passivity of materials in a pure
ethanol or E85 environment. It is thus necessary to make
an assumption about the anodic/cathodic nature of various
materials in an ethanol environment based on a known
galvanic series in an environment such as seawater.
Component Changes for Compatibility
In order to develop a fully compatible ethanol fuel
system, each component was analyzed in terms of
corrosion penetration and galvanic corrosion. All
components were required to be constructed of stainless
steel or anodized aluminum and all seals were
flurohydrocarbon elastomers. In the entire system, not one
component fully met the requirements as specified, and all
components were therefore replaced or duplicated with a
suitable material.
Fuel Pump
An ethanol compatible fuel pump and gasket was
supplied by Delphi to replace the non compatible stock unit.
The main areas of concern for the compatibility of the fuel
pump was with the internal seals of the pump and the fact
that the pump was not completely electrically shielded.
Due to the high electrical conductivity of E85, there is a
possibility that a non-shielded pump and fuel level sensor
could ignite the fumes within the tank.
Flexible Fuel Lines and Hard Plastic Lines
The factory flexible fuel lines and the hard plastic
lines connecting the pump to the steel hard lines were
reported to be non-ethanol compliant by GM and were
replaced with Teflon lined stainless steel braided lines.
However, the factory push-lock connectors were retained
in order to connect these lines to the fuel pump, since
there were not any replacement connectors available. The
o-rings in these connectors were replaced with Viton B orings
to comply with specifications.
Steel Fuel lines
The carbon steel fuel lines were not considered
E85 compatible, due mostly to the possibility of galvanic
coupling of the steel line with more noble materials.
Corrosion byproduct clogging the fuel injectors and leading
to a lean burn condition and the eventual self destruction
of the engine was a possibility. The carbon steel lines were
thus duplicated with a set of Type 304 stainless steel lines
which retained all of the original factory positions.
Because of the higher volumetric fuel flow required for
E85, the fuel lines were tested to assure flow capability to
sustain 5.7L fuel requirements at pressure . The stock line
diameters of 3/8" on the supply line and 5/16" on the
return line were found to be satisfactory and were
maintained.
Fuel Filter
The fuel filter was replaced with an ethanol
compatible filter manufactured by Paxton Fuel Systems as
shown in Figure 7. The outer casing was anodized
aluminum with the inner element of stainless steel mesh
screen. Due to its length, the use of the filter required
slight modifications over the original configuration which
was accounted for on the replacement stainless fuel lines.
Fuel Rails
The compatibility of the factory fuel rails was
unknown and they were therefore replaced with anodized
aluminum fuel rails designed to our specifications and
manufactured by FORCE Corp., as shown in Figure 8. The
original over-the-manifold H-style rail connection was
replaced with a U-style connection fabricated with Teflon
lined tubing. The U-style was chosen for manufacturing
purposes and to allow the addition of a supplemental
throttle body fuel rail.
Supplemental Fuel Rail and Injectors
A supplemental fuel rail (shown in Figure 9), which
was designed to accept 3 additional injectors, was added
for cold start purposes and fuel enrichment at high engine
RPM (see Injector Control). The fuel rail and throttle body
were constructed from anodized aluminum. The
supplemental injectors were provided by Siemens, and
were fully ethanol compatible with a flow rate of 4 g/s.
Addition of the supplemental rail required the alternator to
be pivoted out on its lower bracket, and a 2" longer
accessory belt was installed to accommodate this change.
Pressure Regulator
The U-style fuel rail made it possible to install an
E85 compatible variable pressure fuel regulator to replace
the stock pressure regulator. The regulator was fully
adjustable from 40 psi to 150 psi, however the fuel pump
was only capable of approximately 70 psi maximum. The
regulator was installed between the fuel rail and return line
to assure accurate fuel rail pressure.
Fuel Injectors
A dedicated ethanol engine requires 15-20% more
fuel due to the lower energy content of ethanol. The OEM
fuel injectors were replaced with ethanol compatible
injectors supplied by Delphi. Because the OEM injectors
flowed at approximately 65% duty cycle, it was only
necessary to increase the flow rate 15% over the 5.3L
gasoline injectors. The new injectors (shown in Figure 10)
flowed 3.8 g/s and were acceptable for all engine speeds.
The flame arrestor was designed to meet
competition requirements provided by GM and Argonne
National Laboratory (ANL). The design consisted of a type
304 stainless steel housing containing two pipes, one with
a 1.25” O.D. and one with 2.25” O.D. These dimensions
allowed the OEM fuel fill and vent lines to be pulled over
the stainless steel tubes and clamped with a hose clamp.
A 12" section was removed from the original fuel fill and
vent line to accommodate the flame arrester design.
Inside of the stainless steel tubes is a 40 mesh
304 stainless steel screen. The inside mesh is rolled in a
9“ long cone shape. The cone is intended to maximize the
amount of fuel flow through the mesh as well as optimizing
mesh surface area the fuel will be in contact with. The
mesh will dissipate any heat entering the fuel fill hose from
the outside and break up any propagating flame front.
The outside mesh is connected at the top, forming a cone
as well. The mesh is welded to the stainless steel tubing
to insure long-term placement of the cones.