Environmental Engineering Reference
In-Depth Information
taBle 9.4
correlation between Biodiesel Properties and Feedstock saturation level
saturated
monounsaturated
Polyunsaturated
Fatty acid
12:0, 14:0, 16:0, 18:0,
20:0, 22:0
16:1, 18:1, 20:1, 22:1
18:2, 18:3
Cetane number
High
Medium
Low
Cloud point
High
Medium
Low
Stability
High
Medium
Low
Source:
McGill, R., Aakko-Saksa, P., and Nylund, N.O., Final Report, Annex XXXIV: Biomass-Derived
Diesel Fuels, Task 1: Analysis of Biodiesel Options. IEA Advanced Motor Fuels Implementing
Agreement, Wieselburg, Austria, 2008 and Adapted from National Renewable Energy Laboratory
(NREL), Biodiesel Handling and Use Guidelines , 3rd ed. U.S. Department of Energy, Golden,
CO, 2006. Available at http://www.nrel.gov/vehiclesandfuels/npbf/pdfs/40555.pdf.
exhaust emissions (Prankl et al. 2004; Bacha et al. 2007; White Paper 2007). However, a reduction
of these emissions can be achieved with the use of cetane improver additives, such as 2-ethylhexyl
nitrate (McCormick 2005; Bacha et al. 2007).
Concerning the fuel quality requirements, the requested cetane number changes from one regu-
lation to the other. This is the result of the strong dependence of this parameter on vehicle technol-
ogy, climate conditions, and the regional diesel fuel regulations (White Paper 2007). However,
because of the high cetane number of biodiesel, even the strict requirements of the EU [minimum
51 cetane (ISO 5165)] do not eliminate any known feedstock.
9.2.7 c loud p oint and c old f iltEr p lugging p oint
Cloud point (CP) and cold filter plugging point (CFPP) are two properties used to control a fuel's
cold-temperature behavior. CP expresses the temperature at which a cloud or haze of crystals is
formed within the fuel sample when it is cooled (Prankl et al. 2004; McGill et al. 2008; Rilett and
Gagnon 2008). CFPP describes the fuel filterability at low ambient temperatures (Prankl et al.
2004) and expresses the lowest temperature at which the fuel can pass through the filter in a stan-
dardized filtration test (WWFC 2006). These parameters are mainly an issue with middle distillate
fuels that contain straight- and branched-chain hydrocarbons (e.g., paraffin waxes). When the ambi-
ent temperature approaches the CFPP, the viscosity of the fuel increases and at the point that falls
below the cloud point, these waxes become solids (WWFC 2006; Bacha et al. 2007). This partial
solidification in cold weather may cause blockages of fuel lines and filters, leading to fuel starvation
and problems during engine startup and driving and engine damage due to inadequate lubrication
(White Paper 2007; McGill et al. 2008). Even when the fuel reaches the CP it may still be used as
long as the temperature remains at this point and the filters do not clog (McGill et al. 2008).
Cold-temperature properties of biodiesel vary according to the feedstock and the process (Rilett
and Gagnon 2008). The biodiesel derived from long-chain saturated fatty acids, such as animal
fats and frying oils, have higher cold-temperature values than the unsaturated fatty acids, such as
most vegetable-oil derived biodiesel fuels (Foon et al. 2005; White Paper 2007; McGill et al. 2008;
Table 9.4).
In general, biodiesel has a higher CP and CFPP than petroleum-based diesel fuel (Foon et al.
2005; Rilett and Gagnon 2008). However, improvement of cold-flow properties can be achieved
with the use of special additives or by blending it with winter-grade diesel fuel (WWFC 2006;
McGill et al. 2008). Most of these additives are polymers that interact with the wax crystals that
form in diesel fuel when it is cooled below the cloud point (Bacha et al. 2007). Moreover, engine
 
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