5.1.2. Formation of NO2 at short distances
Significant concentrations of NO2 were found in the drop-tube furnace at stoichiometric and fuel-rich equivalence ratios and at short distances from the atomiser. Nitric oxide formed before 150 mm can give place to NO2 by the well known mechanism of reaction of NO with HO2, or by reactions with hydroperoxyl radicals (RO2). The HO2 mechanism would be favoured by the low flame temperature, as the formation of this radical is inversely dependent on temperature. High concentrations of HO2 radicals are likely to be found in low temperature regions where oxygen is present (see section "4.1.2. Formation and emission of NO2" in chapter I). Although the stoichiometry in the initial stages of the combustion system is fuel-rich, diminishing concentrations of oxygen can provide the conditions for HO2 formation (Cernansky and Sawyer (1974)) .
Other reactions of NO2 formation are also important at low temperatures below 900 °C, such as (Cernansky and Sawyer (1974)) :
HNO2 + O  NO2 + OH
| reac 26
|
| NO + O3 NO2 + O2
| reac 27
|
| HNO2 + OH NO2 + H2O
| reac 28
|
and are likely to occur as amounts of NO are found in early stages of the flame.
Pollutant formation and interaction in the combustion of heavy liquid fuels
Luis Javier Molero de Blas, PhD thesis, University of London, 1998
© Luis Javier Molero de Blas
