OCR Text |
Show fuels. In Figure 5 the various symbols represent different base fuels. Those symbols shown with a line refer to distillate or residual fuels doped with pyridine or thiophene. It can be seen that both total and fuel NO increase with increasing fuel nitrogen content, and that total fuel nitrogen level is the dominant factor controlling fuel NO formation in this system. The form of the nitrogen does not appear to significantly influence fuel NO formation under excess air conditions, as doping with a volatile nitrogen compound (pyridine) resulted in NO emission similar to that from a less volatile residual oil of the same nitrogen content. Since the data is for a system where very fine oil droplets (approximately 25 micron mean diameter) are well-dispersed in the oxidizer under hot fuel-lean conditions, it is not surprising that fuel NO emissions are somewhat higher than those achieved in practical systems. Figure 6 shows fuel NO production as a function of total nitrogen content for petroleum,shale and coal-derived liquid fuels. Under the conditions tested it appears that the fate of fuel nitrogen in alternate fuels is similar to that in petroleum-derived fuels. Figure 7 presents the same data plotted as a percentage of the fuel nitrogen converted to fuel NO . It can be seen that for low nitrogen contents conversion decreases rapidly from greater than 90 percent, and eventually becomes almost independent of the fuel nitrogen content. In summary, testing in the tunnel furnace indicates that fuel nitrogen is the only first order fuel composition parameter controlling NO formation in fuel-lean flames. This conclusion applies to petroleum,coal and shale-derived liquid fuels. However, there appear to be second order effects where the volatility of the fuel nitrogen compound does have an influence upon fuel NO formation. Compare the data for the fuels with fuel nitrogen content of approximately 0.24%. The highest conversion is achieved with a shale-derived distillate fuel with a large volatile nitrogen fraction. 7-13 |