Abstract:
The main aim of this study is to determine the
effect of equivalence ratio and pressure on the formation of
nitrogen oxides (NOx
) in homogenous ignition of methane/air,
methanol/air and methyl formate/air. A constant volume
reactor of 200 cm3
, at initial temperature of 1300 K and at
pressure, P, ranging between 1-50 atmospheres has been
considered. The equivalence ratios of the test mixtures have
been varied from 0.7 to 1.3. This represents the lean-to-rich
region which is most relevant to the conditions in an internal
combustion engine. CH4
, CH3OH and CH3OCHO flames have
been modelled with different detailed reactions mechanisms,
which have been modified and extended to incorporate high
pressure oxidation reactions. Flame structures, minor species
and NOx
time histories have been plotted for the three fuels
under different conditions. The results obtained show that the
formation of NOx
vary with pressure and equivalence ratios.
NO mole fraction profiles and other radicals; N2
, N, O, OH, CH,
HCN, and N2O that are dominant in formation of NO have been
compared. It is established that in homogenous system, NO
formation is high in CH4
at lean and stoichiometric conditions
while CH3OCHO has high NO at rich conditions for all
pressures. At fuel lean and stoichiometric conditions, as
pressure increase from 1 to 50 atm peak NO formed in all the
three fuels increases. At fuel rich condition, as pressure increase
from 1 to 50 atm peak NO formed in all the three fuels decrease.
High concentration of N2
, O, OH and high temperatures
observed in all flames indicate that Zel’dovich mechanism is the
main NO formation route in a homogenous reactor.
