Environmental Engineering Reference
In-Depth Information
4-cylinder diesel engines have been the most frequently employed [144]. Since
engine characteristics might have some influence on the effects of biodiesel, this
information has to be taken into consideration.
8.3.1.1 Effect of Biodiesel on Engine Performance Properties
Brake effective power and power output
. The power output delivered with biodiesel
is reduced with respect to that delivered with diesel fuel at full- and partial-load con-
ditions even with the accelerator fully pressed down. Although reductions around
8% (corresponding to loss of heating value) would be expected in most cases, results
show some variations according to literature reports. Kaplan et al. [133] compared
sunflower-oil biodiesel with diesel fuel at different engine speed and load regimes,
in a 2.5 L, 53 kW engine. The loss of torque and power varied from 5% (at low
speed) to 10% (at high speed). Çetinkaya et al. [136] compared waste-oil biodiesel
with diesel fuel in a 75 kW 4-cylinder common rail engine under full-load condi-
tions. The loss of torque was in the 3-5% range when biodiesel was used to replace
diesel fuel. The authors pointed to the reduced heating value in biodiesel as the most
plausible explanation for this reduction. Similar results were achieved by Lin et al.
[142] in a naturally aspirated 2.84 L diesel engine running with diesel fuel, biodiesel
from palm-oil and a 20% biodiesel blend. The loss of power at full load was around
3.5% with pure biodiesel and 1% with the blend. Similar results in terms of power
loss have also been reported elsewhere [145, 146].
Some authors have claimed that there is a relationship between power losses
and the reduction in heating value. Yücesu and Ilkiliç[147] measured reductions
in torque and power of 3-8% when pure biodiesel from cottonseed was utilised.
Interestingly, they also reported for biodiesel a heating value 5% inferior to that
of diesel fuel. Difficulties in the fuel atomization (rather than the loss of heating
value) was claimed to be the cause of the power loss. Other tests using biodiesel
from waste cooking oil in a marine outboard 3-cylinder naturally aspirated engine
at full load resulted in a power loss of 7.14% as compared with diesel fuel [148].
The difference in the biodiesel/diesel heating values was interestingly very close to
this value. Dorado et al. [138] found a slight increase (5.7%) in the maximum engine
power using waste olive oil methyl esters instead of diesel fuel. Only after the engine
run on biodiesel for 50 h, a minor 2% loss in maximum power was observed.
There are also some publications reporting unexpected increases in engine power
and torque when using biodiesel. Altiparmak et al. measured a 6.1% increase in
maximum torque compared to diesel fuel when 70% tall-oil biodiesel blended with
diesel fuel was used [149]. Although the increased cetane number was used to
explain these findings, the unusually high values of density and viscosity of the
tested biodiesel (922 kg/m
3
and 7.1 cSt at 40
◦
C, respectively) could also partially
explain such results. Similarly, an increase in torque and power was observed in an
indirect injection diesel engine running at 1500 and 3000 rpm on different blends
of diesel fuel with biodiesel from tobacco seed oil (with a lower heating value of
39.8 MJ/kg) [150]. The 17.5% biodiesel blend showed the highest values of torque,
power, density, viscosity and improved combustion, despite the reduced heating
value of biodiesel.
