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Show The decomposition routes of complex reducing agents such as urea and cyanuric acid are not currently well understood. This leaves some uncertainty as to how these materials should be treated during modeling. Cyanuric acid (HNCO)3 was assumed to decompose Into either HNCO or HOCN. For urea, more complex chemicals such as biuret may result from pyrolysis, thus leading to a more complex set of final decomposition products. Since kinetic data are available for only a few rather simple species, It is necessary to assume that urea Is essentially a combination of simpler species such as: ~ 2NH2 + CO ~ NH2 + H + HNCO ~ NH3 + HNCO Previous calculations (Chen, et aI., 1988; Muzio, et al, 1989) have shown that only the latter product set (NH3 + HNCO)resulted in an acceptable prediction of NOx reduction with urea Injection. Figure 2 (a,b) shows the calculated NOx reductions and N20 production, respectively, as a function of temperature for ammonia (NH3), cyanuric acid (as HNCO), and urea (as NH3 + HNCO) addition. These calculations are for the baseline condition described previously at an additive-to-NOx molar ratio (NINO) of 2.0. The calculated NO reductions for NH3 injection are 970;0 with peak removals occurring at 1200oK. Calculated NO reductions for urea injection (NH3 and HNCO) show peak removals at 13000K with the peak removals somewhat less than ammonia. For cyanuric acid injection (HNCO), peak removals of 90% occur at 1300oK. Also, as seen in Figure 2a, the calculated temperature window with HNCO is narrower than NH3 or urea. Calculated N20 emissions corresponding to the NOx reductions in Figure 2a are shown in Figure 2b. As seen In Figure 2b with NH3 injection, very little N20 is calculated as a product, with a peak level of 1 ppm at a temperature of 1200oK. This is consistent with experimental results reported by Lyon (1976) and Muzio and Arand (1976). For the assumed scenario for cyanuric acid decomposition(HNCO), and for urea (NH3 + HNCO), the calculations peak N20 levels of 90 and 68 ppm respectively at 1200oK. For all chemical additives essentially no N20 is found at temperatures above 1300oK. 6 |