Environmental Engineering Reference
In-Depth Information
Similar results have been reported considering a wider range of vehicle engine
sizes. An increase of 2.5 and 14% in BSFC were obtained in a diesel engine running
on 20% biodiesel/diesel fuel blend and pure biodiesel, respectively [158]. The per-
formances of biodiesel from soybean and waste-oils compared in a 57 kW engine
showed the feedstock did not have any influence on the BSFC [158]. Senatore et al.
tested a 1.9 L diesel engine with rapeseed-oil biodiesel, and found that the increase
in BSFC with biodiesel was proportionally related to the decrease of the lower heat-
ing value [159]. Similar results were reported for such biodiesel in a single-cylinder
diesel engine tested in three steady modes [160].
Many research efforts have carried out in order to ascertain the implications of
the properties of biodiesel in the BSFC. The increase in BSFC was reported to be
similar to the loss of heating value in biodiesel from waste oils tested on a 2.2 L
diesel engine [161]. Monyem and Van Gerpen tested a 4.5 L diesel engine with
differently oxidized soybean-oil biodiesel [162]. The increase in BSFC was 13.8
and 15.1% for non-oxidized and oxidized biodiesel (peroxide index of 340 meq/kg).
This difference was attributed to the different heating value of both fuels. Most
authors have explained these increments by the loss of heating value, although some
others attributed them to the different densities of biodiesel and diesel fuel [163].
Nevertheless, some reports moved away from these correlations and claimed no
proportionality between the increase in BSFC and the loss of heating value. A 3.3
and 16.7% increase in BSFC (compared to the use of diesel fuel) were observed
when using a 20% blend and pure palm-oil biodiesel, respectively [142]. Similarly,
Hess et al. [164] found a 18% increase using pure biodiesel from soybean oil. In
contrast to these findings, Silva et al. reported no significant changes in BSFC in a
6-cylinder 9.6 L diesel engine fueled with 5 and 30% sunflower-oil biodiesel/diesel
fuel blends [146]. Similarly, Dorado et al. [138] evaluated the use of waste olive
oil methyl esters during a 50-h short-term performance test in a 3-cylinder 2.5 L
diesel engine and found a very slight BSFC increase. Nevertheless, the statistical
analysis showed no important differences between biodiesel and No. 2 diesel fuel
tests. Kaplan et al. also claimed that the fuel consumption decreased with biodiesel,
causing a reduction in the emitted smoke and soot (smoke opacity) [133].
8.3.1.2 Diesel Engine Exhaust Emissions Using Biodiesel
Several approaches have found that, in general, biodiesel lead to less emissions
(e.g. CO
2)
of the most regulated pollutants compared to standard diesel fuel.
Biodiesel may then contribute to reduce greenhouse gas emissions [165-167].
Provided its oxygenated structure, biodiesel causes lesser particulate formation and
exhaust emissions compared to diesel fuel, resulting in substantially lower unreg-
ulated emissions of carcinogenic compounds (i.e. ketones, benzene and aromatic
compounds).
Smoke opacity is a direct measure of smoke and soot. Various studies show that
smoke opacity for biodiesel is generally lower [133, 168, 169] with much lower
emissions of hydrocarbons. This is also due to oxygenated nature of biodiesel
where more oxygen is available for burning and reducing hydrocarbon emissions
