Using Petroleum and Biomass-Derived Fuels in Duel-fuel Diesel Engines - Novel Combustion Concepts for Sustainable Energy Development - page 239

characteristics of syngas and biogas fuels. Studies dealing with the use of syngas
and biogas in dual-fueled diesel engines are discussed in Sect. 4 , and a summary is
provided in the last section.

2 Conversion Methods

Biomass can be converted to more valuable energy forms through a number of
processes including mechanical or physical, biological, and thermochemical. A
review of various conversion processes and major products (fuels) produced from
ligocellulogic biomass is provided by Gill et al. ( 2011 ). An example of mechanical
process is the extraction of oil from the seeds of biomass crops, such as oilseed rape
and groundnuts. This oil can be used directly for the production of energy or
processed using esteri cation to produce biodiesel. Examples of biological methods

include the production of biogas from anaerobic digestion or the breakdown of
biodegradable material, such as municipal waste and plant material, through
microorganisms (Lin and Tanaka 2006 ), and the fermentation of sugar to produce
ethanol and other biofuels.
Thermochemical methods, which include direct biomass combustion, pyrolysis
and gasification, have been extensively investigated for the conversion of biomass
to a variety of products, including thermal energy, fuels, and chemicals. Direct
biomass combustion has traditionally been used to supply heat and power in the
process industry. Systems utilizing direct combustion of agricultural waste include
kilns and boilers for generating steam used for various industrial applications
including electricity production. As discussed by Werther et al. ( 2000 ) in their
review paper, the typical sequence of events through which a lump of solid fuel
undergoes during combustion includes heating up, drying, devolatilization, ignition
and combustion of volatiles, and finally the combustion of char. In general, the

route involving direct combustion of biomass for electricity generation has low
overall ef

cant pollutants (Caputo et al. 2005 ). For the
details of these processes, and the discussion of many operational and environ-
mental challenges, the reader is referred to their review paper.
Pyrolysis refers to the thermal decomposition of biomass in the absence of
oxygen. Depending on the process variables, such as the reactor temperature and
residence time, it yields various amounts of gaseous, liquid, and solid products of
varying compositions. Conventional pyrolysis, which has been utilized for thou-
sands of years, involves lower temperatures and longer residence times with the
principal product being the solid char. In contrast, fast pyrolysis involves high
temperatures (

ciency and emits signi

≈ ° ≈

2 s), with the main product
being a dark brown liquid or bio-oil along with other gaseous, liquid, and solid
products, including char. This process is much more commonly used at present
compared to conventional pyrolysis. The bio-oil consists of a complex mixture of
oxygenated hydrocarbons with varying but appreciable amount of water from both
the original moisture and reaction product. Proximate analysis of the bio-oil gives a

500 C) and short residence times (