The equivalency ratio effect on the CO emissions
The equivalency ratio, which is the ratio of the actual fuel concentration in the actual fuel-air
mixture over the fuel concentration in the stoichiometric mixture, has a direct effect on the CO
produced from the fuel combustion reactions. As it can be clearly seen from the figures CO
emission from the burnt gas fuels dramatically increases with the equivalency ratio starting from
equivalency ratio 0.6 ,0.8 , 1 , 1.2 till 1.4 respectively under the same range of temperatures. That’s
due to the fact that in the lean mixtures which contain more excess air than fuel (ER<1), there are
enough number of O2 molecules that allow the oxidation of the CO molecules to CO2. While in
the case of the rich mixtures (ER >1), at which the mixture contains an excessive proportion of
fuel comparing to the air, the number of O2 molecules which are provided from the air becomes
insufficient for oxidizing the CO molecules to CO2 molecules.
Comparison of CO emissions by the three different fuels
From this graph, it can be clearly seen that the maximum amount of CO emissions is produced
from the butane fuel, followed by the CO emissions emitted by the DME. However, the lowest
CO emissions were produced by the methanol fuel. By comparing these results to the theoretical
studies, these results are in agreement with the theoretical fact that the amount of CO produced is
a function of the carbon content or the number of carbons in the fuel (EIA, 2020). Therefore, since
the butane has the highest number of carbons (4 carbons) in its molecular formula comparing to
the dimethyl either (DME) which has only (2 carbons) and the methanol which has only 1 carbon,
it has correspondingly the highest CO emissions.
Comparison of CO2 emissions by the three different fuels
Same thing
CO versus CO2 emissions
The relationship between the CO and CO2 emissions for the same fuel under the same
temperature range at a fixed pressure of 1 atm and equivalency ratio of 1 was studied in
order to clarify the complementary relationship between the emitted CO and CO2 from. It
can be easily observed that, as the CO emission increases, the formation or the CO2
emission decreases and vice versa .This is due to the conversion of the CO molecules ,
that at high reaction conversion , most of the CO molecules oxidized into CO2 molecules
so as shown in the figure , the CO2 emission becomes high whereas the CO emission
becomes low and vice versa.
Pressure effect on the CO emissions from the butane, DME and
methanol fuels
the effect of the pressure on the CO emissions by the three fuels (butane, DME and methanol) was
studied at a fixed equivalency ratio of 1 ,and a fixed temperature at 1500 K.
It can be seen clearly that as the pressure increases, the CO emissions from all of the three fuels
decrease. So, from this figure, it can be concluded that the CO emissions can be reduced by
increasing the operating pressure during the combustion process. This result actually completely
agrees with the experimental findings. That it was found by increasing the pressure, an effective
contact between the reactants and a faster reaction rate are achieved at high pressures, so CO
emission produced.
Residence time effect on the CO emissions from the butane, DME
and methanol fuels
Here, by studying the residence time and CO emissions at fixed ER , P and T .It was noted that, as
the residence time inside the reactor increases, the CO emission decreases. And that’s meet the
experimental and the theoretical findings that more time the fuel molecules spend inside the
reactor, more molecules react, so that leads to higher conversion of the CO into CO2 molecules