| OCR Text |
Show of total N O x were at a minimum under stoichiometric conditions. 3. Fuel-rich conditions (q> = 1.20) The absence of oxidising species at fuel-rich conditions caused emissions of NO to be almost negligible for the fuels studied (M1, G1 and G2). Conversely, high concentrations of N 0 2 were measured. Fuel M1 (0.32 % N) produced 253 ppm-wet N02 , whereas lower amounts were obtained from other fuels with lower nitrogen contents: 149 ppm-wet from fuel G 1 (0.13 % N) and 98 ppm-wet from fuel G 2 (0.06 % N). Given the low emissions of nitric oxide at fuel-rich conditions, shown in Figure 2, emissions of total-NOx were determined by those of nitrogen dioxide. They were of the same order of magnitude as those in fuel-lean conditions. b. Effect of sulphur on NOx emissions As explained in the experimental section, the effect of increased concentrations of fuel-sulphur was assessed by the injection of S02-gas into the combustion system. Figures 5 through to 12 present the effect of increasing amounts of sulphur emissions on nitrogenous compounds. 1. Fuel-lean conditions (<p = 0.833) A net reduction of NO emissions was observed from all fuels investigated. The largest nominal reduction was obtained from Orimulsion, with 23.4 ppm-wet (8.71 % of the initial emissions) on addition of 1.5 % fuel-S, whereas smaller reductions were obtained from the heavy gas oils M1, G 1 and G2. These decreases were within a narrow range, between 5 and 11 ppm-wet on addition of 2 % fuel-S, and were seemingly independent of the initial fuel-nitrogen and -sulphur contents. The results can be seen in Figure 5. As explained in previous paragraphs, only emissions of N 0 2 from Orimulsion were significant at 33.5 ppm-wet. However, this value was not substantially altered by the addition of S 0 2. The reductions of N O x emissions obtained at fuel-lean conditions were thus determined by those of nitric oxide. Orimulsion had the largest nominal reduction of NOx emissions, and it is expected that a larger addition of sulphur could cause a further reduction. Smaller decreases of N O x emissions were achieved with the heavy gas oils M1.G1 andG2. 0.5 1.0 Fuel-S added, % Figure 5: Nominal change of NO emissions at 0.833 with increasing amounts of sulphur <P = 9 |
