OCR Text |
Show N 0 2 will be not reduced. As a result, the ratio [NO]/[N02] will decrease. Tseregounis and Smith 17 pointed out that N O can be reduced to N 2 by the action of amine species. Removal of H radicals by sulphur would result in lower amounts of N radicals and higher amounts of NHi radicals. In a similar way the increase of N 0 2 concentrations can be explained by the radical recombination assisted by S 0 2 . N 0 2 is known to disappear by reaction with radicals such as O and H, although the amount of O radicals is expected to be low in these conditions. Thus, further reduced concentrations of these radicals will lead to higher concentrations of N 0 2 . 3. Fuel-rich conditions (<p = 1.20) Enhancement of N02 in the presence of hydrocarbon species has been documented previously. However, no report has been found on the effect of S 0 2 on N 0 2 in fuel-rich hydrocarbon systems. Two possible processes may be altered by the presence of S 0 2 leading to an increase the N 0 2 concentrations measured. O n e is the enhancement of radical species that form N 0 2 , such as H 0 2 or hydroperoxyl radicals (R02). Interaction between hydrocarbons, sulphur and nitrogenous compounds in fuel-rich conditions was studied by Corley and Wendt 5 . Not only soot particles contained amounts of nitrogen, but the amounts of soot collected decreased on addition of S 0 2 . Experimental results on Orimulsion combustion at cp = 1.20 obtained concurrently to this experimental 40i 35- „ 30- a> |25- E a. 5s 2 15^ <3 10- 5- Ol --•-- Ml --•--G1 ^# ' - * - G 2 ^- ''" .+-'"' „ - y 4 f . / / ^^^~~*~~ " ' ^^^^^^ K ^ - •- 1 ^X. 1 ^-- ' 1 0.0 0.5 1.0 Fuel-S added, % 1.5 Z0 Figure 11: Nominal change of N 0 2 emissions at q> = 1.20 with increasing amounts of sulphur 13 work ,J showed a decrease of solid matter emissions with the addition of S 0 2 , which confirms the existence of interactions between S and hydrocarbon species. In stoichiometric and fuel-rich conditions the measured exhaust concentrations of C 0 2 decreased on addition of S 0 2 . This suggests that the latter makes combustion less complete as reduced sulphur species and carbon monoxide may compete for oxidising compounds in this oxygen-deficient atmosphere. A s the amounts of C 0 2 decrease, those of carbon monoxide and hydrocarbons will therefore increase. It is also likely that the concentrations of hydroperoxyl radicals (R02) will rise, leading to increased concentrations of N 0 2 . However, more information about the process of N 0 2 formation by R 0 2 radicals must be known before a thorough rationale can be established. N o information is available about this process at the temperatures found in combustion operation. 14 |