Page 457 - Advances in Eco-Fuels for a Sustainable Environment

410 Advances in Eco-Fuels for a Sustainable Environment

15.2 Ecofuels in CI engine

A compression ignition (CI) has higher brake thermal efficiency (BTE) than the spark
ignition (SI) engines. Due to the higher power development, it is being used a power
source for heavy duty applications. With the world inching toward these alternative
energy sources, the present and future automobiles are designed to meet this alterna-
tive trend. Many ecofuels have been used in CI engines in the recent past such as alco-
hols, biogas, hydrogen, and CNG.

15.2.1 Methods of fueling alternative fuels in CI engine

All the alternative fuels cannot be used directly in a diesel engine due to the variations
in their properties. Therefore, fewer modifications need to be done in order to run the
engine in a smooth manner. The present section focuses on the various states of alter-
native fuels that can be used in diesel engines.

15.2.1.1 Liquid fuels

Alcohols are viable and feasible alternatives that are presently used in the form of
additives in small quantities with petroleum fuels under various operating conditions.
Among various alcohols, methanol, a low carbon alcohol mainly produced from syn-
thesis gas (hydrogen and carbon monoxide (CO)) in the presence of catalyst. In addi-
tion, varieties of feedstock have been tried for methanol production by various
researchers. The diesel engine operations with alcohol at various concentrations were
shown to have a comparable performance with lower exhaust emissions. However, the
corrosive nature of alcohols would cause poor material compatibility long term, espe-
cially with rubber and some specific metals [9]. Biodiesel is another liquid cleaner
biofuel that is produced from any renewable feedstock such as vegetable oil and ani-
mal fats through the transesterification processes. Most of these biodiesel fuels could
be easily blended up to 20% by volume with diesel that can produce the same perfor-
mance of diesel fuel at a substantial penalty in NO x emissions [10]. Further, the same
existing infrastructure might be used for biodiesel storage applications.

15.2.1.2 Gaseous fuels

CNG is an important and feasible gaseous fuel that is relatively very cheap, environ-
mentally friendly, safe to handle, and has abundant available energy resources. By
considering the availability and infrastructure facility, CNG seems to be a prominent
alternative fuel for diesel engine applications. Earlier reports revealed that CNG fuel
could stand well below conventional fuel for the consideration of performance
aspects, but the emissions aspects might give a strong driving force for its commer-
cialization in the automotive sectors. Interestingly, the widened availability and excel-
lent storage infrastructures are the dominant factors that pay the way for its selection
as one of the best alternative fuels at the moment. Fig. 15.2 shows the schematic dia-
gram of conversion of biogas to CNG.