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Eco friendly biofuels for CI engine applications 417

oxygen content in the biodiesel, the better the BTE. It is also a fact that pure biodiesel
shows better BTE than biodiesel blended with additives. This characteristic is attrib-
uted to the reduction in the ratio of biodiesel in the fuel blends as it results in a decrease
in the net calorific value of the fuel.

15.3.4.2 Brake specific fuel consumption

BSFC is a measure of the fuel efficiency of any engine that burns fuel and produces
rotational power output. The BSFC value indicates how efficiently the engine con-
verts fuel supplied into useful work. One of the main parameters used to determine
the characteristics of biodiesel on BSFC is calorific value. The higher the calorific
value, the lower the BSFC because a reduction in the calorific value of a fuel results
in a rise in the fuel consumption for attaining the corresponding power output.
Although biodiesel has higher higher calorific value but still it is lesser than diesel
which results in higher BSFC than the diesel fuel at all loads. Another parameter that
decides the performance characteristics of biodiesel is the oxygen content present in
the fuel. This is because a higher oxygen content of biodiesel helps to facilitate better
combustion. Varying the engine load also plays an important role in studying the per-
formance characteristics of biodiesel. Studies have shown that increasing the engine
load from zero to full load shows a decreasing trend in the BSFC and the brake specific
energy consumption decreases.

15.3.5 Combustion characteristics of biodiesel
Various combustion characteristics such as heat release rate (HRR), cumulative
HRR, in-cylinder pressure, peak pressure, and ignition delay are used to study the
properties of biodiesel under various conditions. All the combustion parameters are
interdependent.

15.3.5.1 Ignition delay

Various parameters of biodiesel govern the ignition delay of a CI engine. One impor-
tant parameter that determines the ignition delay is the cetane number, and the higher
the cetane number, the lower the ignition delay and hence the better the combustion.
Biodiesels have a high cetane number, thus they have a lower ignition delay and there-
fore fast combustion. The cetane number in biodiesels is higher than diesel, hence they
have a lower ignition delay. Other parameters such as biodiesel type, biodiesel quality,
air-fuel ratio, engine speed, quality of fuel atomization, intake air temperature, oxygen
content, and viscosity of biodiesel are also significant factors affecting the ignition
delay. The higher the viscosity of the biodiesel, the larger the ignition delay because
viscosity affects fuel atomization and evaporation. It also affects the mixing of fuel
with air [17]. Also, the higher oxygen content of the biodiesel aids in enhancing
the combustion process. Engine load also affects the ignition delay considerably.
Increasing the engine load from zero to full load results in a decrease in ignition delay
as the gas temperature inside the engine cylinder increases.