Environmental Engineering Reference
In-Depth Information
high electrical conductivity signifies a high risk of corrosion and thus clogging of the fuel systems
and injector deposits (WWFC 2008).
In contrast to bioethanol and bioethanol blends, gasoline is an electrical insulator. As a result,
this specification is not important for low percentage blends but is significant for higher content
ethanol, such as E75 and E85 (IFQC 2004). In practice, flexible-fuel vehicles (FFVs) use this differ-
ence of conductivity between ethanol and gasoline and are equipped with a sensor for the measure-
ment of electrical conductivity in the fuel. In this way, they determine the ratio of the bioethanol
blend and optimize its combustion parameters, such as injection, ignition time, and quantity of air
(IFQC 2004).
The test of bioethanol electrical conductivity is a relatively simple and cheap way to measure its
corrosiveness and ionic contamination (WWFC 2008). Brazilian specifications limit this parameter
to the level of 500 μS/m maximum for anhydrous and hydrous ethanol (method NBR 10547:2006).
Although, CEN and ASTM specifications do not yet include any limit for the electrical conductiv-
ity of bioethanol, the EU and United States are considering adding the same limit as Brazil (White
Paper 2007).
9.3.7 E
thanol
c
ontEnt
The ethanol content is an indicator of bioethanol quality (WWFC 2008) and identifies the pres-
ence of contaminants such as water, methanol, and higher alcohols in bioethanol (White Paper
2007). Although bioethanol is originally a pure product, during the production process several con-
taminants may decrease its ethanol content (White Paper 2007). Moreover, the denaturing process
reduces the ethanol content (e.g., undenatured bioethanol with 99.0% v/v will fall to 94.0% v/v after
denaturing) (Gray 2005).
Bioethanol with slightly lower ethanol content than normal may influence the engine perfor-
mance rather than harm any of its parts (White Paper 2007). This effect is less important for FFVs
than optimizing the fuel combustion by adjusting the air-to-fuel ratio according to the ethanol
content of the fuel (see Section 9.3.6). Sometimes, lower ethanol content is even suggested to pro-
vide better cold-start and warm-up performance by increasing fuel volatility (RFA 2009). From the
other side, very low ethanol content may affect the lubricating properties of the fuel and its water
tolerance (IFQC 2004). Moreover, low ethanol content usually indicates high methanol content.
Methanol is toxic and when it is present in bioethanol in concentrations higher than 2.5% v/v it may
cause corrosive problems (RFA 2009), lower the water tolerance, and increase the vapor pressure
of the fuel (IFQC 2004).
Currently, the United States has set its limit at 93.9% v/v minimum (ASTM D5501 method),
whereas the EU limits the ethanol content to 96.8% v/v (indirectly from the ethanol + C
3
-C
5
alco-
hols limit, i.e., ethanol + C
3
-C
5
at 98.8% v/v and C
3
-C
5
alcohols at 2% v/v) and Brazil at 99.6% v/v
(ASTM D5501 method). However, all three countries have agreed to move toward a common 98%
v/v (ASTM D5501 method) limit (White Paper 2007).
Apart from ethanol content, there are some more specifications that determine the ethanol or
other categories of alcohol in bioethanol. These specifications are in use for the moment, but they
will be eliminated in the near future because their importance is questionable because of the use of
ethanol and water content specifications (White Paper 2007). Briefly, as already mentioned, the EU
limits ethanol plus heavier (C
3
-C
5
) alcohol content (EC/2870/2000 Method I, Appendix II, Method
B) and C
3
-C
5
alcohol content (method EC/2870/2000—Method IIIb) separately (Costenoble 2006).
The United States also has a limit for C
3
-C
5
alcohol content (4.5% v/v maximum on the basis of
the ethanol, water, and methanol content limits). The EU and United States have a specification for
methanol content (i.e., 1.0% v/v, maximum; ASTM D5501) and 0.5% v/v maximum (EC/2870/2000
Method III), respectively. Brazil specifies HCs at 3.0% v/v maximum (ABNT NBR 13993 method)
and total alcohol (ethanol plus methanol plus heavier alcohols) content of ethanol produced by
fermentation of sugarcane at 99.6% v/v minimum (density method similar to ASTM D4052). By
