Page 467 - Advances in Eco-Fuels for a Sustainable Environment

420 Advances in Eco-Fuels for a Sustainable Environment

such as lack of oxygen, air-fuel mixing, fuel injection timing, and fuel atomization. It
has been observed that with the increase in engine load, smoke emission reduces due
to the increasing combustion temperature within the cylinder. It can be noted that the
smoke emissions is decreased for biodiesel for the increment in engine load, however
at full load condition the smoke emission is increased due to the rich fuel region and
oxygen inadequacy locally inside the combustion chamber. Many studies have
observed that biodiesel produced less smoke than diesel [19]. This can be attributed
to the presence of oxygen and decreased carbon in the biodiesel that promotes com-
plete combustion of the fuel during the stage of diffusion combustion.

15.3.7 Tribological aspects of biodiesel
The tribological properties of fuels play a vital role in ensuring a long engine lifespan
because they determine the wear experienced by the engine on running. The raw mate-
rials used for the production of biodiesel play an important role in determining the
engine tribology characteristics. In addition, higher viscosity, lower volatility, and
the reactive nature of unsaturated hydrocarbon chains of biodiesel affect the engine
by leading to injector coking, trumpet formation on the injectors, more carbon
deposits, and thickening and gelling of the engine lubricant oil after the engine has
operated with biodiesel for a long period of time. Adequate modifications to the
engine such as an increase in injection pressure, turbocharger installation to increase
in-cylinder temperature and pressure, and usage of improved lubricants and additives
are required to improve the performance, combustion, and emission characteristics of
the engine while improving lubricating oil degradation.

15.4 Biofuels in CI engine

Using biofuels in CI engines decreases not only the need for diesel demand but also the
particulate matter emitted from the engine without compromising the engine perfor-
mance. Biofuel, for example, alcohol and biodiesel, could partly decrease petrol fuel
utilization, decrease harmful emissions, and, more importantly, decrease the life-cycle
emission of CO.

15.4.1 Alcohols in CI engine

Alcohol blends with diesel can contribute to a significant reduction of engine exhaust
emissions and dependency on oil. Alcohols are appropriate additives to diesel because
they are rich in oxygen content and are found in liquid nature. Low-carbon alcohols
such as methanol and ethanol have gained attention as additives to diesel fuel due to
their simpler production technologies and rich oxygen content, which significantly
improves the combustion characteristics while reducing emissions from the engine.
Fig. 15.8 shows a schematic of conversion of plant biomass into higher alcohols by
the influence of bacterial action (Table 15.3).