Page 472 - Advances in Eco-Fuels for a Sustainable Environment

Eco friendly biofuels for CI engine applications 425

15.4.1.4 Tribological aspects of alcohols

Wear can be defined as any damage to the engine surface in terms of material loss due
to the relative motion between the moving parts. The parts that are most likely to get
damaged are pistons, cylinders, piston rings, bearings, and crankshaft valves. Com-
mon problems that arise in the engine when diesel is substituted with alcohol are
blocking of the fuel injector, carbon deposits, sticking of the piston ring, and wear
of the engine; this mostly occurs because of mixing of unburned oil gases into the
crankcase [27] The loss of lubricating oil viscosity and pressure leads to a loss of load
carrying capacity and aggressive wear. But sometimes the presence of oxygen in bio-
fuel reduces the wear of important components of the engine. As investigated by sev-
eral researchers, it has been found that the carbon deposition on CI engine components
generally originates due to thermal and oxidative degradation of the lubricating oil and
incomplete combustion. These deposits degrade the engine, decrease the efficiency,
and cause operational problems; sometimes heavy deposits can cause total engine fail-
ure. These carbon deposits increase with continual usage of biofuels. One of the solu-
tions is to use high cetane number oxygenated additives such as dimethyl ether and
diethyl ether, along with diesel or biodiesel blends to reduce such deposits.

15.4.2 Low viscous low cetane fuels in CI engine

Generally, fuels that are less viscous and have a lower cetane number as compared to
standard diesel are regarded as low viscous low cetane (LVLC) fuels. Such fuels are
likely to have less viscosity and low cetane number due to a relatively shorter carbon
chain length and absence of fatty acids. These fuels can also be considered light
biofuels [36]. Unlike vegetable oils that are extracted from seeds, these fuels originate
from different plants or biomass. Some of the fuels with such traits are alcohol-based
fuels such as methanol, ethanol, butanol, and other higher alcohols; furthermore, there
are plants-based light biofuels such as eucalyptus oil and pine oil. Focusing upon
plant-based biofuels, light oils show emerging possibilities in the field of alternative
fuels for diesel engines and extensive research is under way to optimize the opera-
tional capabilities. Eucalyptus oil is known to show an analogy with the naphthenic
base in the molecular structure [37]. This expedites its characteristics to act as a
cosolvent. Moreover, the major constituent of pine oil is 1,8-cineole, which is derived
from biomass and oleoresin, during the tapping of pine trees [38]. Although it can be
seen that both eucalyptus oil and pine oil are dissimilar in their chemical structure
when compared to lower alcohols, they are designated as alicyclic hydrocarbon with
double bonds and therefore plant-based LVLC fuels are seen to have a lower cetane
index. Usually, the cetane index is seen to drop with the increase in the number of
double bonds in the molecular formula [39].

15.4.2.1 Performance characteristics of LVLC fuels

Engine parameters that delineate the performance characteristics of the engine such as
BTE and BSFC are discussed in detail in the following section.