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Show 1.8 ^ X 1.6 - 1.4- 1.2- #*., z 1.0- 2 0.8 - z 0.6- 0.4- v ^><\ N**-A^ <k. 0.2- 0.0- •-- - •-- 1- --•-- Ml - - • - - G1 * G2 * •^""'^^^ *^ ^^*~A~^»_ ^-•.TT^Tr^*^ - * -. 1 1 1 0.0 0.5 1.0 Fuel-S added, % 1.5 2.0 The effect of increased sulphur on N 0 2 in fuel-rich conditions had varying results, according to the fuel. Figure 11 shows this feature in greater detail. Fuel M 1 showed increases of up to 37 ppm-wet on addition of 2 % fuel-S as S02. This represented a 14.6 % increase over emissions in the absence of S02. Fuel G 2 exhibited a smaller increase of N 0 2 emissions, 12.1 ppm-wet (6.4 % per 1 % S added), whereas fuel G1 had a negligible variation of N 0 2 emissions with S 0 2 addition. Thus, N O x emissions were increased by addition of sulphur to the combustion system at fuel-rich conditions. Calculations of the percentage increase of N O x emissions yielded the results shown in Figure 12. Maximum increases of N O x emissions were presented by fuel M1, whose emissions increased by 15 % (39 ppm-wet) with addition of 2 % fuel-S. Intermediate increases of N O x emissions were obtained from fuel G 2 (11.4 %, ie 13.6 ppm-wet), whereas the lowest increases were obtained from fuel G 1 (3.5 %, ie 5.4 ppm-wet). The transformation of S 0 2 into other reduced sulphur species in this oxygen-deficient environment is again shown by the lower increase of the exhaust concentrations of sulphur dioxide with respect to the calculated values. Figure 8: Plot of [NOJ/fNOJ vs percentage of fuel- S added for the fuels investigated at q> = 1.00 Discussion 1. Fuel-lean conditions (q> = 0.833) The experimental results demonstrate that sulphur (as S02.gas) is able to reduce emissions of N O x in fuel-lean conditions. No large differences were found in the nominal reductions of N O emissions from the heavy gas oils studied, which possess very different fuel-N and -S contents. Furthermore, no correlation seems to exist between these and the decreases achieved, as can be observed in Figure 5. This fact suggests that the interaction of S with N O occurs by a mechanism which is independent of the fuel-N and S contents and also of the 5 T 1.0 Fuel-S added, % 2.0 Figure 9: Nominal change of N O x emissions at <p = 0.833 with increasing amounts of sulphur 11 |