Page 465 - Advances in Eco-Fuels for a Sustainable Environment

418 Advances in Eco-Fuels for a Sustainable Environment

15.3.5.2 In-cylinder pressure

The pressure inside the engine cylinder is an important parameter that has to be mon-
itored during the combustion process to study the performance characteristics of the
CI engine. It is dependent on the amount of fuel taking part in uncontrolled combus-
tion. Various parameters of a biodiesel govern the cylinder pressure of the CI engine,
such as high latent heat of vaporization, specific heat, heat of reaction, and ignition
delay. All these parameters play an important role in deciding the combustion char-
acteristics of a biodiesel. High cylinder gas temperature accompanied with low latent
heat of vaporization, low specific heat with higher heat of reaction, and lower ignition
delay are the characteristics of a good biodiesel. The cylinder peak pressure is deter-
mined mainly by the combustion rate of the biodiesel in the initial stages, which is
influenced by the uncontrolled heat release phase of the biodiesel. The cylinder peak
pressure is lower than that of standard diesel, which can be attributed to the high vis-
cosity and low volatility of biodiesel. Studies have also shown that the cylinder peak
pressure of a biodiesel increases with rise in the engine loads because the amount of
the biodiesel injected into the cylinder increases with the rise in engine load.

15.3.5.3 Heat release rate
HRR is a crucial combustion parameter obtained by applying the first law of thermo-
dynamics on the in-cylinder gas pressure variable. It is in using HRR that the phases of
combustion are classified. The different combustion phases are premixed combustion
phase, mixed-phase combustion phase, and late combustion phase. Various studies
show that the total duration of combustion is shorter for biodiesel compared to stan-
dard diesel. Because biodiesel poses a high calorific value, it shows a good HRR.
However, in comparison to diesel, the characteristics are low. As the calorific value
of the biodiesel blend is lower than diesel, a higher quantity of fuel is consumed to
keep the engine speed stable at different loads.

15.3.6 Emission characteristics of biodiesel
Various emission characteristics such as NO x emission, CO emission, carbon dioxide
emission, hydrocarbon emission, and smoke emission are used to study the properties
of biodiesel under various conditions.

15.3.6.1 Hydrocarbons

Hydrocarbon emissions result because of the biodiesel that is completely unburned or
partially burned. It arises due to the improper air-fuel mixing and is also dependent on
various factors such as biodiesel properties, oxygen content, heat of vaporization, fuel
injection parameters, and fuel operating conditions. As the engine load is increased
from zero to full load in most cases, HC emission is decreased. Biodiesel shows
low HC emission compared to neat diesel, which can be attributed to the presence
of high oxygen content within the biodiesel fuel molecules and also due to the high
cetane number. Biodiesels have higher viscosity than diesel fuel, which causes better