The NHi pathway

In the presence of amine-like nitrogen compounds in combustion a reservoir of NH radicals is generated. Depending on factors such as temperature, pressure and the air:fuel ratio, reaction products such as N2, NO and N2O are formed. In Figure 9.2 the most important reactions of NHt radicals in flames are summarized.

The NH2 radical is the dominant specie under lean-burning conditions. By increasing the fuel:air ratio more hydrogen atoms are formed, by which more

1000

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)

INJECTION TEMPERATURE. K

1000

INJECTION TEMPERATURE. K

Figure 9.2 Reaction scheme showing the oxidation of NH radicals in flames

Source: Adapted from Miller and Bowman (1989)

Figure 9.2 Reaction scheme showing the oxidation of NH radicals in flames

Source: Adapted from Miller and Bowman (1989)

NH radicals and nitrogen atoms are generated. The most important reaction leading to N2O formation under flame conditions is the reaction:

However, under these conditions N2O is destroyed very quickly by its reaction with H atoms and/or OH radicals. Only if the local flame temperature is in the region of 1000K is a significant formation of N2O observed.

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