OCR Text |
Show 2. Stoichiometric conditions (<p = 1. 00) Conversely, addition of sulphur caused a drastic increase of N 0 2 emissions from all fuels investigated, in larger amounts than the reductions of N O , (see Figure 7). Although with some degree of scatter, the largest increases of N 0 2 emissions were obtained from fuel M1, with smaller increases from the heavy gas oils - 31.7 ppm-wet from fuel G1 (ie, 46.4 % of the emissions without 4-, 2 = n i "5! I -2- E a, Oa -4- Z -6 J <] -8- -10- -12- r T • •- H - ^"""^"-"^ X 1 ~x - *> C - --•-- Ml - - • - - G1 * G2 1- *^.>- ^ ^ \^ * ^ ^ "i k . \ . \ \ ^ *N T Lx \^ s>^ " "x s *» .._ t. "*• • 1 1 -- ..-a • -». '"*-<> 0.0 0.5 1.0 Fuel-S added, Figure 6: Nominal change of N O emissions at q> = 1.00 with increasing amounts of sulphur addition of S) and 16.3 ppm-wet from G 2 (ie, 52 % of the baseline emissions). The extent of the increase followed the order of nitrogen content of the fuels (see Table 1 for fuel specifications). 15 2.o -rne combined effect of added sulphur on both N O and N 0 2 was increased emissions of total-NOx from all fuels studied (see Figure 10). The increase is largest for fuel M1 (23.6 ppm-wet, ie 24.2 % of the initial N O x emissions, on addition of 2 % fuel-S) although it seems to stabilise after the initial increase of 0.5 % fuel-S. Moderate increases were obtained from fuels G1 and G2, approximately 10 ppm-wet per 1 % fuel-S added for fuel G1 and 3.5 ppm-wet per 1 % fuel-S added to fuel G2. It is worth mentioning the change of the relative amounts of N O and N 0 2 found at stoichiometric conditions. Figure 8 shows a graph of the [NO]/[N02] ratio vs percentage of fuel-S added. The fact that the measured increases of S 0 2 at exhaust were lower those calculated from the flow rate of 0.5 i.o 2.o dopant may suggest that it is reduced Fuei-s added, % to other sulphurous species which may play an active part in the N O reduction processes. 35-i 30- ~ 25- S 5 E 20- a. Q. C?15- 2 < 10- 5- Oi _ " / -V -•-- Ml -•--G1 • ^ - G 2 ,-+ ,* + * • -- * - .^*' J** ' *' .'' * ' ^A S ~' ^^ * ^s^ * •> y ^ 1 1 1 1 Figure 7: Nominal change of N 0 2 emissions at 9 = 1.00 with increasing amounts of sulphur 3. Fuel-rich conditions (q> = 1.20) The addition of fuel-S to the combustion system had little effect on N O emissions at fuel-rich conditions. Most readings increased by 2 ppm-wet which, added to the fact that N O readings were very small, resulted in a negligible effect of sulphur. 10 |