Environmental Engineering Reference
In-Depth Information
design changes to address this problem include locating the fuel pump and filter at the spot where
they will receive the most heat from the engine or the pumping of more fuel to the injectors than the
engine requires (Bacha et al. 2007).
Because of the dependence of the cold-temperature properties on a given climate, it is difficult to
define a specific value of cold-flow performance even on a national level. The specification for this
parameter is under discussion to avoid the elimination of any feedstocks and to prevent an overly
large difference in cold-flow requirements between biodiesel and fossil diesel (White Paper 2007).
9.2.8 c
arBon
r
ESiduE
The carbon residue value of a fuel defines its residue-depositing tendencies (Prankl et al. 2004;
Bacha et al. 2007; White Paper 2007; Rilett and Gagnon 2008). The limit of this parameter refers
to the amount of carbonaceous matter left after evaporation and pyrolysis of a fuel sample under
specified conditions (Prankl et al. 2004; White Paper 2007; Soriano 2008). Although this residue is
composed of more than carbon, the term “carbon residue” is a commonly accepted phrase (Prankl
et al. 2004; White Paper 2007).
Carbon residue has proven to be one of the most important indicators of the quality of bio-
diesel because this parameter has a direct correlation with the content of glycerides (Mittelbach
et al. 1992), free fatty acids, soaps, and remaining catalysts or contaminants (Mittelbach 1996).
Additionally, the carbon residue is influenced by high concentrations of polyunsaturated FAME
and polymers (Prankl et al. 2004; White Paper 2007). Hence, the carbon residue can be an indicator
for the coking tendency of fuel. Moreover, the carbon residue is indirectly correlated with engine
deposits (Bacha et al. 2007; Rilett and Gagnon 2008).
Because of the significance of this parameter, its limitation is included in biodiesel specifications.
However, the method that has to be used is under discussion. Some countries, such as the United
States [0.050% m/m maximum (ASTM D4530)], India [0.05% m/m maximum (ASTM D4530)],
and Brazil [0.10% m/m maximum (EN ISO 10370/ASTM D4530)], have decided to use a 100%
sample in the place of 10% because of the similar boiling point of most biodiesel fuels that makes it
difficult to leave a 10% residual on distillation. Alternatively, countries such as the EU [0.30% m/m
maximum (EN ISO 10370)], Japan [0.3% m/m maximum (JIS K 2270)], and Australia [0.30% m/m
maximum (EN ISO 10370)] acknowledge this difficulty and are still skeptical because the precision
of the 100% method is still uncertain (White Paper 2007).
9.2.9 a
cid
n
umBEr
The acid number (or neutralization number) of a biodiesel determines the level of mineral and
free fatty acids contained (Prankl et al. 2004; White Paper 2007; Rilett and Gagnon 2008). For
the case of diesel, in which there are neither free fatty acids nor degradation of byproducts, the
acid number determines the amount of mineral acids (Rilett and Gagnon 2008). The acid number
is defined as the milligrams of potassium hydroxide (KOH) required to neutralize 1 g of FAME
(Prankl et al. 2004; White Paper 2007). The acid number may be correlated with the copper
strip corrosion number (see 9.2.5) because some sulfur and acid compounds can induce the latter
(White Paper 2007).
The acid number can ensure the absence of free fatty acids (Prankl et al. 2004; Singh 2005) and
is directly related to oxidation stability (Rilett and Gagnon 2008). A high acid number in a biodiesel
sample is associated with fueling system deposits (mainly on pumps and filters) and leads to filter
clogging and other fuel system malfunctions (Foon et al. 2005; Rilett and Gagnon 2008).
Acid number varies according to process and feedstock (Rilett and Gagnon 2008). The type of
feedstock used to deliver the biodiesel and the degree of refinement are two of the factors that influ-
ence the acid number. Moreover, the production process (mineral acids or degradation by-products)
and aging during storage influence the acid number of biodiesel (Cvengros 1998).
