Kinetics of nitrous oxide formation during combustion

The formation of N2O as a by-product during combustion has been well known for many years. The gas-phase formation/destruction of nitrous oxide is strongly linked to gas-phase NO kinetics and more specifically to the transformation of cyanide species into NO and N2 in the so-called 'fuel-NO mechanism'.

The presence of amines or other organic N compounds in fossil fuels -'fuel-bound nitrogen' - is of paramount importance for the formation of N2O. Kramlich et al (1989) reported a significant increase in the N2O concentration by adding nitrogen-containing compounds such as ammonia (NH3), hydrogen cyanide (HCN) and acetonitrile (CH3CN) to a gas flame in the temperature range 1050-1400K. The results of this study are shown in Figure 9.1. It is quite evident that N2O formation is limited to a relatively small temperature range. These results, together with the findings of Miller and Bowman (1989) and Hayhurst and Lawrence (1992), provide further evidence that N2O formation in combustion occurs by homogeneous gas-phase reactions through the so-called NH; or HCN pathways.

Figure 9.1 N2O formation after adding NH3, HCN and acetonitrile into the exhaust of a gas flame as a function of temperature

Source: Kramlich et al (1989)

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