Ford's answers to the NHTSA 6.7 Investigation

However, it has also been reported that the formation of corrosive materials (such as organic acids,
water and methanol), polymers, gum formation, thermal and oxidative instability and water
separation may give rise to vehicle operability problems. The following vehicle operability
problems have been identified during extensive field trials as being caused by these fuel
characteristics:

• Corrosion of Fuel Injection Equipment (FIE) components
• Elastomeric seal failures
• Low pressure fuel system blockage
• Fuel injector spray hole blockage
• Increased dilution and polymerisation of engine sump oil
• Pump seizures due to high fuel viscosity at low temperatures
• Increased injection pressure

As a first step in this study, it was necessary to establish the product qualities of the diesel base fuel
and biodiesels nominated for the work programme. These chemical and physical properties were
compared against the relevant National Specification of ASTM D6751 and BS EN 14214. All fuels
were found to meet the requirements of the Standards.
The soy-based biodiesel was then oxidised under specified conditions to a minimum level of
oxidation as determined from the acid number. To meet the fuel requirements of the study, two
batches of soy biodiesel (batch 1 and 2) were prepared separately resulting in two different levels of
oxidation. Both fuels failed to fulfill the requirements of the standard. The oxidised soy biodiesel
used to prepare the B20 blends was oxidised to a much greater extent than is likely to be
encountered in actual commercial use. This was intended to serve as a worst case example, but in
fact may have been so highly oxidised as to be unrealistic. The subsequent separation of this heavily
oxidised B20 blend into two phases suggested that this might be because of the high degree of
oxidation. Analytical work was undertaken by the Associated Octel and the National Renewable
Energy Laboratory (NREL) to investigate the physical and chemical characteristics of the separated
oxidised fuel blend.
The separation of the highly oxidised biodiesel blend prompted additional investigation. One
additional fuel blend was formulated to determine the behaviour and pump wear effects of a B20
blend prepared from a less highly oxidised soy biodiesel. Limited analysis was conducted to
measure fuel properties and one further common rail pump test was performed to determine pump
wear effects of this biodiesel fuel blend.


Examination of the pump following the test on the B20 blend containing highly oxidised soy
biodiesel revealed a hard lacquer accumulation on one of the pump components and significant seal
swell. This candidate fuel concluded without operational failure but significant fuel separation was
noted. A further common rail test on a less highly oxidised B20 blend was concluded without
operational failure and without evidence of fuel separation or signs of lacquering. Swelling of one
of the seals in the test pump was again noted.
No unusual wear was found on any of the common rail test pumps used in the study. The rating
measurements from the common rail pump lubricity tests concluded that the fuels were within the
range which would normally be expected for commercial automotive diesel fuels.
The evidence indicates that phase separation of B20 blends prepared from oxidised biodiesel did not
occur in storage. Decomposition reactions occurring under the conditions of test probably
accelerated fuel separation in the more highly oxidised B20 test fuel containing very high levels of
water and sediment. Phase separation did not take place in the B20 fuel containing biodiesel
oxidised to a lesser extent and which contained lower water and sediment. The main factor
therefore affecting the different behaviour of the oxidised fuels is thought to be the extent of
oxidation.

• The highly oxidised B100 biodiesel and biodiesel blends prepared for this study have
significantly different physical and chemical characteristics to non-oxidised biodiesel and
biodiesel blends. The B20 test blend containing highly oxidised biodiesel may have been
more highly oxidised than is likely to occur in the real world.
• Fuel filter blocking and fuel separation was observed during testing of the highly oxidised
B20 test fuel in this study. Products of oxidation in the test fuel and decomposition
reactions occurring under the conditions of test probably accelerated fuel separation in the
fuel blend. Fuels likely to present this composition cannot be recommended for use for
commercial automotive fuels.

The ratings produced from pump lubricity tests indicate that all test fuels are within the
range normally expected for commercially available automotive diesel fuel running under
the test conditions selected for this 500 hour test procedure. The rotary pump wear test on
the highly oxidised B20 blend failed due reach completion due to fuel filter blockage. It
should be noted that commercial decisions around lubricity quality should not be based on
the results of single test.