Using Petroleum and Biomass-Derived Fuels in Duel-fuel Diesel Engines - Novel Combustion Concepts for Sustainable Energy Development - page 241

signi cantly depending on the source and production process, the main constituents

include CH 4 (50 75 % by volume), CO 2 (25 40 %), N 2 (0 10 %), and small traces

- - -

of H 2 O, O 2 ,H 2 , and hydrogen sul de, as well as some contaminants such as volatile

organic compounds, and halogenated hydrocarbons. Some representative biogas
mixtures based on the two common sources, namely agricultural waste and house-
hold waste, are provided by Quesito et al. ( 2013 ). Like natural gas and syngas,
biogas can be used as a transportation fuel in IC engines, or for power generation in
gas turbines and boilers. It can also be used as compressed natural gas, or reformed to
produce syngas, or in solid oxide fuel cells to generate electricity.

3 Syngas and Biogas Combustion and Emission
Characteristics

3.1 Syngas Combustion and Emission Characteristics

Considerable work has been reported on syngas combustion and emission char-
acteristics (Lieuwen et al. 2009 ; Cheng 2009 ; Aggarwal 2013 ). Fundamental
studies have focused on various aspects, including the development of thermo-
transport and kinetic models, and examining the ignition and combustion charac-
teristics in both laboratory fl flames and practical devices. A major challenge iden-

ti ed in these studies is due to substantial variation in its composition and heating

value. This requires that the fundamental properties, such as adiabatic flame tem-
perature, laminar burning velocity,

flame stability, extinction,
and blowout, need to be determined for a wide range of syngas composition. This
also presents challenges while designing syngas combustors, requiring optimization
for locally available fuels. Table 1 lists the heating values and adiabatic

fl flammability limits, fl

fl ame

temperatures (T ad ) of various syngas-air mixtures at = 1.0. As indicated, T ad is

nearly independent of the syngas composition. However, diluents, such as CO 2 ,
H 2 O, and N 2 , can be used to modify its value. Syngas typically has lower heating
values compared to biogas and other hydrocarbon fuels. For example, the higher
heating value for syngas with 50 %CO and 50 %H 2 by volume is 18,943 kJ/kg or
284,139 kJ/kmol, while the corresponding values for methane (representative of
biogas) are 55,500 kJ/kg and 888,000 kJ/kmol, respectively.
Detailed mechanisms for syngas oxidation have been developed by Davis et al.
( 2005 ), Li et al. ( 2007 ), Wang et al. ( 2007 ), and K

ϕ

s et al. ( 2013 ). Since the
oxidation chemistries of H 2 and CO are fundamental to those of hydrocarbon fuels,
the mechanisms developed for latter fuels, such as the GRI-3.0 (Smith et al.) and
San Diego ( 2002 ) mechanisms, have also been used for syngas combustion. Val-
idations for the mechanisms have been provided using ignition delay and laminar
fl

é romn è

flame speed data. Ignition delays have been measured using a variety of devices,
including shock tube (Petersen et al. 2007 ), rapid compression machine (RCM)
(Walton et al. 2007 ), and constant volume (or constant pressure) reactor, while